Gerhart Drews

Photosynthesis Research 48: 325-352, 1996.

(~) 1996Kluwer Academic Publishers. Printedin the Netherlands.

Personal perspective/Minireview

Forty-live years of developmental biology of photosynthetic bacteria* Gerhart D r e w s Institut fiir Biologie 2, Mikrobiologie, Albert-Ludwigs-Universittit, Schtinzlestr. 1, 79104 Freiburg, Germany Received 1 January 1996; accepted in revised form 20 March 1996

Key words: assembly of light-harvesting complexes, bacterial photosynthesis, chromatophores, intracytoplasmic membranes, membrane differentiation, bioenergetics, photophosphorylation, oxygen tension, light intensity, phototaxis, cyanobacteria, purple bacteria, chlorosomes, electron microscopy, cell wall, lipopolysaccharides, peptidoglycan

Abstract

Developmental biology and cell differentiation of photosynthetic prokaryotes are less noticed fields than the showpieces of eukaryotes, e.g. Drosophila melanogaster. The large metabolic versatility of the facultative purple bacteria and their great capability to adapt to different ecological conditions, however, aroused the inquisitiveness to investigate the process of cell differentiation and to use these bacteria as model system to study structure, function and biosynthesis of the photosynthetic apparatus. The great progress in research in this field paved the way to study principal mechanisms of cellular organization and differentiation in these bacteria. In this article, the history of the research on membrane structure and development of anoxygenic photosynthetic prokaryotes during the last 45 years is described. A personal account of how I entered the field through research on the phototaxis of cyanobacteria is given. Intracytoplasmic membranes (ICM) were detected by electron microscopy in cyanobacteria and in purple non-sulfur bacteria. The formation of ICM by invagination of the cytoplasmic membrane in purple bacteria was observed for the first time. Investigations on the effect of changes in oxygen tension and light intensity on the formation of pigments and intracytoplasmic membranes followed. The isolation, purification, and analysis of lightharvesting complexes and of pigment-binding proteins was the next step of our research. Lipopolysaccharides and peptidoglycans were detected and analyzed in the outer membrane of photosynthetic bacteria. Functional membrane differentiation includes variations in the rates of photophosphorylation and electron transport. Molecular genetic approaches have initiated the investigation of transcriptional regulation and the analysis of correlation between pigment and protein synthesis. Molecular analysis of assembly of light-harvesting complexes and membrane differentiation are the present aspects of our research. Cell differentiation has been considered under evolutionary view.

Abbreviations: BChl- bacteriochlorophyll; C M - cytoplasmic membrane; ICM-intracytoplasmic membrane; LH-light-harvesting; RC-photochemical reaction center; Rba.-Rhodobacter; Rsp.-Rhodospirillum; Rps.Rhodopseudomonas The enormous amount of data and theories in modern biology raises the difficulty of grasping the important lines of progress and the essentials of new and farreaching theories. The hard work of generations of * Written at the invitation of Dr Govindjee and dedicated to Martin D. Kamen, who received the 1996 Enrico Fermi Award for the discovery and application of 14C.

scientists who brought together the abundance of data seems to be forgotten, and the way how things came about has faded from awareness. I believe that it should be of interest for the scientific community to learn how the progress in research is influenced by the history of ideas, by the development of new methods, by political and economical events and the last not the least by

328 the personal fortuity of the researcher. It is satisfying to observe that unifying and fundamental principles of metabolic pathways, of energy transduction, of cell differentiation, of signal transduction, and of global regulatory networks have evolved from comparative studies performed by many people and on quite different organisms. Although the number of variations on one theme and the number of analogous structures and mechanisms are bewildering, the underlying major lines of evolution has become visible. The progress in research on photosynthesis and developmental biology in this turbulent and fascinating epoch has been immense. This perspective on structure, function and cell differentiation in photosynthetic bacteria is presented from a personal view and will be interwoven with reflections on the journey of becoming a microbiologist interested in photosynthetic prokaryotes.

1925-1943: Childhood and adolescence

I was born and grew up in Berlin, a wonderful town to live in. The attractive countryside was close to our house. We very often roamed through the landscape of parks, pine forests, and garden suburbs with lakes and castles. The numerous theaters and opera houses with excellent performances, the museums, the concert halls, the zoo with aquarium and terrarium, the planetarium, the botanical garden and the art school attracted me at different stages of my youth. The summer holidays I spent together with my parents on the farm of my grandfather and uncle near Dresden with its beautiful historical section and its nice surroundings. My major interests in school were divided between literature, plays and poetry and chemistry and biology. Friends of my parents opened my eyes to plants and their habitats. I read more books on literature and history during this time than in later years when I was occupied by science. These extracurricular activities reduced my scholastic eagerness during a short period of my school time. Although I was relatively protected from the Nazi ideology by the education by my parents, several good teachers, and friends, my free development and daily life became increasingly impaired by the despotism of the Nazi regime and the war. My carefree youth was burdened with and then lost to the awful experience of human infamy.

University education and research on phototaxis of cyanobacteria

After my military service and imprisonment, I found my parents in the small town of Torgau, because our fiat in Berlin had been destroyed during the war. I enrolled at the University of Halle simply to be close to a family base of maintenance and supply. My initial aim was to study chemistry or medicine, but due to certain circumstances I enrolled in biology, chemistry, geography and educational sciences classes and finished my examinations in 1951. My major field was plant physiology, with a broad background in plant morphology, systematics, and geobotany. On numerous excursions we became familiar with the diverse plant communities in variable ecosystems determined by climatic, geomorphological, and geological factors. During a course in plant physiology, I became acquainted with cultures of cyanobacteria, known as blue-green algae at that time, which I isolated in the greenhouse. I observed that the trichomes moved to the rim of the petri dishes directed toward the light from the north window. I became interested in the mechanism of the light response and was accepted by Professor Johannes Buder as a PhD student to investigate this phenomenon in his laboratory. The motility of bacteria can be traced back to two completely different mechanisms: the swimming movement driven by rotation of flagella, and the gliding movement on surfaces characteristic of filamentous cyanobacteria and myxobacteria. The mechanism of gliding is still unknown, although the movement of cyanobacteria under the influence of light has been known for more than a century (Cohn 1866; Famintzin 1867; Stahl 1880). Experimental work on light-stimulated and light-directed movement of cyanobacteria began in the second decade of this century by Pieper (1913), Nienburg (1916), Harder (1918, 1920), and Schmid (1921, 1923). I selected several representatives having different types of movement. Phormidium uncinaturn and Oscillatoria mougeotii moved relatively fast (up to 200 #m/min) and rotated around their long axis during gliding; Anabaena variabilis and Cylindrospermum licheniformis did not rotate during gliding, moved slowly (about 20 #m/min), and showed hairpin-like bending of the filament during gliding. The equipment for experimental work at this time in the Botanical Institute was very primitive: some glassware, several optical glass filters and interference filters, and a cabinet filled with old microscopes were available for constructing the experimental set-up. No

329 disposable Petri dishes, pipettes and other material, no rooms with constant temperature were available. The light intensity was measured in 'Hefner candles' with a 'grease spot' photometer in the physics department! In addition to the phototaxis group there was a group of students in Buder's lab working with coprophilic fungi, e.g. Pilobolus. New strains were isolated from fresh manure of various wild animals. Typical smells passsed through the laboratories when the cultures were set up and when the glass culture vessels were cleaned. The third group in the lab was working on histology of chimeric plants. They were despised by the experimentally working students! With the help of our mechanic, equipments were constructed to follow the phototactic reactions of a mass of cyanobacteria or single trichomes, e.g. a small chamber for microscopic observations in which a light field could be projected onto a dark field in order to observe single trichomes gliding from the light into the dark or to keep the anterior end of the gliding trichome in the dark or in the light by moving the stage of the microscope. I observed that the trichomes of Oscillatoria species stopped gliding and moved backwards when the anterior end was exposed to a light intensity lower than that to which the posterior end of the trichome was exposed. As a consequence of this phobotactic ('Schreck' or frighten) reaction, the trichomes assembled in an area of bright light surrounded by a darker field (light trap). Illumination of the anterior end of the trichome with a higher light intensity than the posterior part did not cause a turning back reaction. The sensitivity to the stimulus threshold (the difference between the light intensities outside and inside of the light field) was very high. Red light (615-765 nm) was more effective in positive phobotaxis of Phormidium uncinatum than green and blue light. Positive Topo-phototaxis, that is, gliding toward the light beam, was observed under blue and green light but not under red light (630--900 nm) with Phormidium uncinatum. Filaments of Oscillatoriaceae that were accidentally oriented parallel to the incident light beam (+ 40 o) moved for a longer period of time toward the light than in the opposite direction, like in the Echternacher spring procession (the repeated taking of three steps forward and two steps backward until one has reached the destination). Filaments oriented perpendicular to the light beam did not show a preferential direction of movement. In contrast, Anabaena and Cylindrospermum were able to adjust their filaments during gliding toward the direction of the light beam (Drews 1959). I concluded that (topo)phototaxis in Oscilla-

toriaceae is the result of a change in the rhythm of forward and backward movements. Illumination from one side causes prolongation of movement toward the light source in filaments that are accidentally oriented parallel to the light beam, while the time of movement away from the light source is shortened. At very high light intensity, the opposite negative reaction was observed. The positive phototaxis of Anabaena and Cylindrospermum in red light is brought about by a steering mechanism, i.e. an active orientation of the filament toward the direction of the light beam (Drews 1959). From these results, it was concluded that the cells can sense differences in light quality and intensity along the filament and/or the flanks of the filament, which are transduced via a signal chain into a change of the direction of movement. I also have shown that specific parts of the spectrum are efficient for each type of the phototactic reaction (Drews 1959). These results were confirmed and and greatly extended by Wilhelm Nultsch and coworkers in TiJbingen and Marburg (1975, 1979, 1985). Action spectra of phototaxis and the contribution of membrane potential and proton motive force in the light response were determined with modern experimental equipment and new approaches. Nultsch was my fellow student in Halle. He investigated in Buder's laboratory the phototaxis of diatoms. The transfer of an electric potential along a filament from the illuminated to the dark portion was shown by Chailakyan et al. (1982). The molecular mechanism of how a light stimulus is transformed into a phototactic response is still waiting for scientists eager to learn more about this interesting behavior of searching for optimum light conditions by active movement. In the plant physiology course that I taught in 1953, we enriched photosynthetic bacteria using the Winogradsky column, which simulates a natural ecological niche. After one or two weeks, a bright purple zone of sulfur purple bacteria became visible. From biotopes near Halle and in Jena, we isolated naturally accumulated suspensions of purple bacteria, e.g. Chromatium okenii, ThiospiriUum jenense and other Chromatium as well as RhodospiriUum species. The phototaxis of purple bacteria was studied by Hans G. Schlegel in Buder's laboratory. In addition to being attracted by the clear and instructive lectures of my instructor Johannes Buder, I was fascinated by the stimulating and vivid lectures in plant biochemistry given by Kurt Mothes. Since no textbooks were available at this time, we did not miss any lectures. I also remember the stimulating lectures

330 in general philosophy and Kant's work by Menzer. Although the living conditions at this time were very restricted and again political freedom was absent we all were young, optimistic and happy to live. Besides my work at the university I taught biology in an elementary school and in a school for nurses to increase my income. At that time, no special lectures and courses in microbiology were offered by the faculty of natural sciences; therefore, I took courses and lectures in medical microbiology and phytopathology in the medical school and in the agriculture departments. Basic knowledge in mycology was attained in the botany department.

Discovery of photosynthetic membranes and granular structures in phototrophic prokaryotes 1953 was the year of the first movement against the communist regime in East Germany. The rebellion was ended by the Soviet army after about one or two days. On the first day, I moved from Halle to Jena, where I met professor Hans KnOll among the protesting people. He was the director of the Institute for Microbiology and Experimental Therapy and known for organizing biotechnology (the first production of penicillin and other antibiotics in East Germany). The institute was a place of relative freedom in research at that time in East Germany. I joined a small group in cell biology. Although the equipment was primitive according to the present-day standards, we were happy to work there. Since the institute produced Mycobacterium bovis BCG for tuberculin vaccine production, I was asked to work with mycobacteria. I investigated the metabolism and cytochemistry of polyphosphates in M. phlei (Drews 1960b,c). However, my major interest was still directed toward photosynthetic bacteria, of which the fine cell structure was completely unknown. Since the institute in Jena had an electron microscopy unit, I investigated, in cooperation with Werner Niklowitz, the ultra structure of several Oscillatoriaceae and Nostocaceae with very simple equipment. Niklowitz used a watchmaker lathe to cut the embedded material. The feed of the block to the glass knife was obtained by squeezing the embedded material. In spite of all the problems we were very excited to see for the first time lamellar structures in the so-called 'chromoplasm', i.e. the peripheral part of the cyanobacterial cell, which appears greenish in the light microscope. The lamellae

were not separated from the cytoplasm by membranes as in chloroplasts but were irregularly arranged in an onion-scale-like pattern and distributed throughout the cytoplasm (Niklowitz and Drews 1956, 1957; Drews et al. 1961). The association of photosynthetic pigments with lamellar structures has been detected in plant and algal chloroplasts in several laboratories (FreyWyssling and Mtihlethaler 1949; Wolken and Palade 1952, 1953; Leyon and von Wettstein 1954; Steinmann 1952; Steinmann and Sj0strand 1955). We concluded that the photosynthetic pigments of cyanobacteria were bound to lamellar structures located in the peripheral part of the cell, not enclosed by membranes as in chloroplasts. The chlorophyll content of isolated lamellae was quantified by Schmitz (1967). The lamellar system of various species differed in their organization. Although the micrographs were of low quality, one could imagine that there were additional structures on the surface of the lamellae, which were later identified as the phycobilisomes (Drews and Golecki 1982). The presence of lamellar structures in cells of cyanobacteria was confirmed by Ris and Singh (1961) and later by many scientists. The numerous granular and fibrillar inclusions of the 'centroplasm' of the cyanobacteria were investigated using electron microscopy and cytochemical methods. In addition to polyphosphates and carbohydrates, redox enzymes were detected in the 'structured' granula (Drews and Niklowitz 1956, 1957). There was clearly no membrane-enveloped nucleus in the cells. Lamellar structures were also detected in the anoxygenic purple bacterium Rhodospirillum molischianum, which was unfortunately confused with Rsp. rubrum (Niklowitz and Drews 1955), but later placed in its correct taxonomic position, and compared with the vesicular membrane structures of Rsp. rubrum (Drews 1960a). We supposed that these structures were homologous to chromatophores, containing the entire complement of photoreactive bacteriochlorophyll and carotenoids, first isolated by ultracentrifugation (Schachman et al. 1952; Pardee et al. 1952) and analyzed by Newton and Newton (1956). In a very early study, the pigments of Rhodospirillum rubrum were described as being associated with proteins as soluble chromoproteins which absorb light at 855 nm (French 1938).

331

The pioneer period of photosynthesis research The demonstration of photophosphorylation, i.e. the light-dependent formation of ATP from ADP and inorganic phosphate, in chromatophores was an important step forward in the functional analysis of the chromatophores (Frenkel 1954, 1956, 1959). In plant chloroplasts, photophosphorylation was independently detected at the same time (Arnon et al. 1954; Arnon 1959). Single chromatophores which are inside-out vesicles from a physiological point of view (ATP-synthase on the outside and H + export from the interior to the outside) were artifacts obtained from cell homogenates by shearing. Electron microscopy studies on 'ghosts' (plasmolyzed cells without cytoplasm) and intact ceils of several species have shown that all chromatophores or lamellar structures are interconnected to each other by delicate tube-like structures (Giesbrecht and Drews 1962; Boatman 1964; Tauschel and Drews 1967; Hurlbert et al. 1974) that have been correctly renamed intracytoplasmic membranes (ICM) by Holt and Marr (1965a,b). We detected by electron microscopy of thin sections that the vesicular or lamellar ICMs (closed sac-like and flattened vesicles = thylakoids) originate de novo by invagination from the cytoplasmic membrane or ICMs (Giesbrecht and Drews 1962; Drews and Giesbrecht 1963; CohenBazire and Kunisawa 1963; Tauschel and Drews 1967). This was a basic observation for studies on morphogenesis of the photosynthetic apparatus. The conclusion that all ICM's together with the CM form a continuous network of vesicles, branched thylakoids or characteristic stacks of closely appressed thylakoid membranes was supported by observations from several laboratories. Highly ordered stacks of thylakoids were found in the newly isolated Bchl-b-containing bacterium Rhodopseudomonas viridis (Drews and Giesbrecht 1965, 1966). The tubular type of ICM was detected by Eimhjellen et al. (1967, 1970). Interestingly, the thylakoids of cyanobacteria seem not to originate by invagination from the cytoplasmic membrane. The finding that chromatophores or ICMs contain the pigments bacteriochlorophyll (BChl) and carotenoids and catalyze photophosphorylation confirmed that the bacterial photosynthetic apparatus is localized in these membranes. The membrane-bound proteinaceous complexes of the photosynthetic apparatus were for the first time visualized by electron microscopy of in vivo freeze-fractured cells of Rps. viridis. The intramembrane particles were arranged in

a regular pattern (Giesbrecht and Drews 1966). These particles have been later identified as reaction center (RC)-light-harvesting I complexes (Jay et al. 1983). Hartmut Michel isolated and crystallized RCs from this strain and determined, together with Johann Deisenhofer and Robert Huber, the first atomic structure of an RC (Deisenhofer et al. 1984, 1985). In the early 1960s, the mechanism of transduction of light energy into the chemical energy of ATP was still a matter of speculation. The first clear experiments showing that the same coupling factor can catalyze photophosphorylation and oxidative phosphorylation were published by Baccarini-Melandri et al. (1970). The discrimination between light-harvesting (bacterio)chlorophyll with the function of absorption of light energy and the transfer of excitation to the reaction center and photochemical reaction centers with the function of charge separation was experimentally demonstrated in the 1950s and early 1960s ('P890' or [BChl]2: Duysens 1951, 1952; Duysens et al. 1956; Clayton 1962; Vredenberg and Duysens 1963; 'P700' Kok 1961; Witt et al. 1961a,b). These new and exciting results induced extensive experimental work on various levels and fields in plant and bacterial photosynthesis. The growing interest in photosynthesis and photosynthetic organisms found its formal verification by the instatement of the international congress in photosynthesis organized every third year beginning in 1968 in Freudenstadt, Germany, organized first by Helmut Metzner. A wine testing with all participants illustrates how small the photosynthetic club was at this first congress. A solid basis for the studies on photosynthetic purple and green bacteria was the comprehensive description of the physiology and taxonomy of photosynthetic purple bacteria by Hans Molisch (1907) and Cornelis B. van Niel (1932, 1944) and isolation of numerous sulfur purple bacteria by Norbert Pfennig (1993). No pure cultures of cyanobacteria existed at this time. The pioneering work of Roger Stanier in Paris provided the basis for modern research in taxonomy, photosynthesis, and molecular genetics of cyanobacteria by establishing the collection of pure clone cultures of cyanobacteria at the Institute Pasteur in Paris. The first international symposium on phototrophic prokaryotes - cyanobacteria, purple and green bacteria - was organized in 1974 by Stanier, Pfennig and myself in Freiburg. This symposium continues to take place every third year, mostly in Europe, alternating with the photosynthesis congress. The increasing interest in these organisms is underlined by the growing number

332 of participants. The early state of art in the research on bacterial photosynthesis was presented at the Yellow Springs meeting in 1963. The book which summarizes the vivid discussions is still recommended for every one interested in that topic (Gest et al. 1963). Several aspects of photosynthesis research are also dealt with in the recollections of illustrious scientists presented on the occasion of Martin Kamen's birthday (Kaplan and Robinson 1982).

Microbiology in Freiburg 1960 was an important year in my life. I was promoted to Dr.rer.nat.habil.( completion of my Habilitation) at the University in Halle and married Christiane, who worked as a head physician at the university hospital for gynecology and obstetrics in Halle. We went together on detours to Freiburg, where I accepted a position as Dozent (lecturer) in the Botany Department of the university. Before 1960, biology in Freiburg, as in most German universities, was represented by chairs in botany and zoology. The two professors holding these positions retired in the same year and were replaced by Hans Mohr and Bernhard Hassenstein. A new faculty with a department system was founded, and in response to the modern development of biology, professors for genetics, plant biochemistry, cell biology, plant physiology, microbiology, biophysics and zoology were appointed during the period from 1960 to 1966. In this decade, natural sciences expanded, new universities were founded, and new institutes were built and received modern equipment. A curriculum for the study of biology was developed, which took into consideration the progress in biology and the necessity of a broad basis for the different fields of biology. After a basic study in biology, chemistry and physics, each student could select a training in three biological and one non-biological speciality, e.g. microbiology, biochemistry, genetics and molecular biology, and physics. In this frame, I developed a curriculum for microbiology, including lectures and courses in biochemistry and physiology of microorganisms and applied microbiology, such as phytopathology, biotechnology and virology. I am thankful to my colleagues from the medical school in Freiburg and at the neighboring universities in Ttibingen and Ziirich who helped me with teaching during the first years before Jtirgen Oelze, Georg Schrn, and Jiirgen Weckesser were appointed in microbiology and contributed to the teaching pro-

gram. In my view, the training in comparative biology for all students of biology at that time was too extensive and shortened the period for training in special disciplines. During the following decades, the curriculum was modified very often. I feel that there should be more free time for the excellent students who do not like to take the easy route to pass examinations. In general, this early awakening period during the late 1960s was very exciting; it was a time of a great optimistic impetus to overcome the large disadvantage in science in Germany because of isolation, emigration of many excellent scientists, and loss of support during the period from 1934 to 1946. In 1964, I was appointed as a full professor in Freiburg after declining a similar position in Ttibingen in 1963, Research programs were developed and supported mainly by the Deutsche Forschungsgemeinschaft. I will not detail my increasingly heavy burden at the University as dean or department head or member of committees, as referee for many national and international organizations, and as editor or member of the editorial board of several scientific journals. The set-back in the prosperity of the universities by the 1968 student revolt and its effect on the following period has to be elaborated historically but cannot be discussed in this article. My greatest interest was always in the scientific work in cooperation with many students, postdoctoral coworkers, and colleagues in the scientific community. Unfortunately, my responsibilities in Freiburg prevented a longer stay at an institute outside of Germany. However, I learned much during my sabbatical leaves, and I am very thankful for the hospitality of Howard Gest (Bloomington, Indiana), June Lascelles and Phil Thornber (UCLA), and Lawrence Bogorad (Harvard University, Cambridge, Massechusetts) for making my sojourn in the USA very fruitful. I was also very pleased when several colleagues and friends from America, Japan and European countries spent their sabbatical leave in Freiburg and contributed to the scientific activities in the institute through their experimental work, seminars, and numerous discussions with members of our institute. These were the Alexander von Humboldt-awardees Martin Kamen, Clinton Fuller, Andrew Staehelin, and Milton Saier. Nestor Cortez, Nikolaj Firsow, Augusto E Garcia, Judith Hoeniger, Ronald Hurlbert, Itzhak Ohad, Toshihisa Ohshima, Bill Richards, Judith Shiozawa, Jon Takemoto, Vladimir Yurkov, and many students and postdocs from abroad, for shorter or longer periods, contributed much to the results obtained on photosynthetic bacteria. A common program was set up for several

333 research groups in Freiburg on the structure, function, and formation of membranes of photosynthetic bacteria. The program was sponsored for eight years by the Deutsche Forschungsgemeinschaft. The results of this productive cooperation - e.g. the resolution of the porin structure of the outer membrane, and progress in structure, function, crystallization and biosynthesis of light-harvesting complexes - were presented in numerous articles and discussed in two international symposia in Freiburg (Drews et al. 1987; Drews and Dawes 1990).

that give an overview on this subject (Drews 1973; Weckesser et al. 1974a,b, 1979; Drews et al. 1978; Drews and Weckesser 1982; Jtirgens et al. 1983). I will also not describe the short period of my work on phytopathogenic bacteria (Drews et al. 1988), which was initiated by my lasting interest in host-parasite interactions, a topic dealt with for decades in lectures and seminars.

The influence of light intensity and oxygen tension on the formation of the intracytoplasmic membrane system

The envelope of eyanobaeteria and purple bacteria Parallel to our studies on the photosynthetic apparatus, we began to investigate the cell envelope of photosynthetic prokaryotes. At this time, detailed studies on this topic were only known from enteric bacteria and bacilli. The cell wall of Cyanobacteria is Grampositive by staining, but the structure appeared to be Gram-negative: a typical outer membrane is underlined by a relatively thick peptidoglycan layer (Golecki and Drews 1982). I was eager to learn more about the chemical composition and macromolecular organization of the cell wall of cyanobacteria and purple bacteria. The first evidence of murein (peptidoglycan) in cell walls of the filamentous cyanobacterium Phormidium was given by Frank et al. (1962). We detected murein in the unicellular species Anacystis nidulans and Chlorogloeafritschii (Drews and Meyer 1964) and lipopolysaccharides in cell walls ofAnacystis nidulans (Drews and Gollwitzer 1965; Weise et al. 1970). These studies were extended by analyses of lipopolysaccharides in purple bacteria by Jiirgen Weckesser in cooperation with colleagues at the Max-Planck-Institute of Immunology, which was at this time a leading institute in the systematic analysis of enteric lipopolysaccharides (Weckesser et al. 1972). Later, systematic investigations on peptidoglycan and lipopolysaccharides in both groups of photosynthetic prokaryotes followed. It was shown that in contrast to the highly conserved lipid A structure in enteric bacteria, which is responsible for the endotoxic effect, different and partially non-toxic lipid A structures were detected in these photosynthetic organisms. From the structure of an untoxic lipid A an immune modulator was developed during recent years. Peptidoglycan of cyanobacteria was found to be covalently bound to a polysaccharide fraction (Jtirgens et al. 1983; Jtirgens and Weckesser 1986). I will not detail the results; instead, I will refer to some articles

It was known for a long time that facultative phototrophic bacteria grow and synthesize BChl only when grown anaerobically in the light (van Niel 1944). The growing interest in photosynthesis in the 1950s and the knowledge of the ability of the facultafive phototrophs to grow alternatively under chemotrophic or phototrophic conditions opened the way for the study of the influence of light intensity and oxygen partial pressure on the synthesis of pigments and the formation of the photosynthetic apparatus. The first systematic study on this subject was initiated by Roger Y. Stanier and his wife Germaine Cohen-Bazire. The creation of this project is nicely described in the recollections of Stanier (1980). It was discovered that the main regulatory factor of the BChl synthesis is the oxygen partial pressure. At high oxygen tension, BChl synthesis is inhibited when the bacteria are growing in the dark or in the light, but BChl is synthesized even in the dark at very low oxygen tensions. The differential rate of BChl synthesis under anoxic conditions was found to be an inverse function of light intensity (Cohen-Bazire et al. 1957). The BChl content of chromatophores isolated from cells grown anaerobically at high and low light intensities was found to be closely correlated with the differences in BChl content of the cells from which they were prepared. It was concluded that the light-induced changes of cellular BChl content reflects mainly changes in the amount of BChl incorporated into the photosynthetic apparatus, rather than changes in the amount of chromatophore material in the cell (Cohen-Bazire and Kunisawa 1960), while Holt and Marr (1965b) concluded that the BChl content of the cell depends on the greater or smaller amounts of membrane that have a constant concentration of BChl. We could later show that both the BChl content of the membrane and the number of intracytoplasmic membrane (ICM) vesicles per cell change upon variation of

334 light intensity, depending on the stage of differentiation (Oelze and Drews 1970, Drews and Oelze 1981, Reidl et al. 1985). At this early stage, the proteinaceous components of the photosynthetic apparatus and the stoichiometric binding of BChl to specific proteins were completely unknown, but a correlation between BChl synthesis and an increase of specific membrane proteins, seen in SDS polyacrylamide gel electrophoresis, was observed (Biedermann et al. 1967; Biedermann and Drews 1968). An increase of specific proteins after lowering of oxygen tension had also been observed in other laboratories (Lascelles 1959; Bull and Lascelles 1963). I remember that I found no interest or response when I asked at that time biophysicists and biochemists concerning the role of polypeptides in the photosynthetic apparatus. The influence of intensity and quality of light and of oxygen partial pressure on growth, protein, and BChl synthesis was studied in parallel to electron microscopic studies on morphogenesis of the ICM in several laboratories. The action spectrum of the influence of light on BChl synthesis in Rhodopseudomonas (Rhodobacter) sphaeroides showed a higher effectiveness of farred light (780-880 nm) than blue and green light at 400-600 nm (Drews and J~iger 1963). A pigment system other than BChl and carotenoids that senses intensity changes at specific wavelengths of the spectrum has not been detected. A five- to ten-fold increase of BChl and carotenoid concentration and in the number of ICM vesicles per cell was observed in cells of several species that were shifted from high light to low light growth conditions (Table 1) (Drews and Giesbrecht 1963; Holt and Marr 1965a,b; Oelze and Drews 1970; Reidl et al. 1985). Rsp. rubrum and Rba. capsulatus can grow in the dark under a broad range of oxygen partial pressures down to about 4 mm Hg (-~ 520 Pa) at the same growth rate. The threshold value of pO2 for the induction of BChl synthesis is species-specific at about 5 mm Hg in Rsp. rubrum, with a maximum at about 3-4 mm Hg; however, BChl synthesis occurs at up to 60-70 mm Hg in Rba. capsulatus (see Tables 2 and 3; Biedermann et al. 1967; Drews et al. 1969; Dierstein and Drews 1974). In other species, e.g. Rhodospirillum salexigens (Drews 1981; Golecki and Drews 1980), Rhodobacter sulfidophilus (Doi et al. 1991), and Rhodospirillum centenum (Yildiz et al. 1991), BChl synthesis is relatively insensitive to changes in oxygen tension. The photosynthetic apparatus of these species is present under chemotrophic and phototrophic growth condi-

~

min

~ . i TO0

~ I

min

~ I eoo

~

rain I

I 900

I

I r,m

700

I

I

800

I

900 n m

Figure 1. Near-infrared absorption spectra at 77 K of the membrane fraction of Rhodobacter capsulatus isolated from cells induced to form the photosynthetic apparatus in the dark by lowering the oxygen tension at time 0 from 53 kPa to 200 Pa. These spectra show that in the first period of about 90 min, reaction center and antenna complex I are formed. After 150 min, the light-harvesting complex II becomes the dominating pigment-protein complex. The absorption maxima axe shifted at the low temperature from 870 to 894 nm (LH I) and from 855 to 857 nm (LH II). From Schumacher and Drews (1978).

i

700

800

900 nm

700

I

800

900 nm

Figure 2. Near-infrared absorption spectra at 77 K of the membrane fraction isolated from Rhodobacter capsulatus. Chemotrophic dark cultures were shifted at time 0 from about 53 kPa to 70 Pa. The cell number per volume do not increase, but pigment-binding polypeptides of the reaction center and light-harvesting I complex are synthesized and assembled in the membrane. Only traces of LH II axe synthesized. See bacteriochiorophyll concentrations in Table 2. From Schumacher and Drews (1978).

tions. These bacteria synthesize BChl in the dark under strict oxic conditions, while R. rubrum does not contain BChl or ICM under these conditions. At very low oxygen tension in the dark, the first pigment-proteins synthesized in Rba. capsulatus are the RC and LH I complexes. LH II was not detectable until 90-150 min after induction (Figures 1 and 2; Tables 2 and 3). These early results of kinetic studies (Schumacher and Drews 1978) were later confirmed and extended by investiga-

335

Table 1. Composition and activities of cells and intracytoplasmic membranes from Rhodobacter capsulatus grown anaerobically in a turbidostat at various light intensities cyt c2 cyt Cl cyt b561 concentrations in mol per mol reaction center

Growth conditions

BChl

UQ

1 high light low light

42 121

64 19

2.51 0.69

1.91 0.4

2.28 0.62

1.28 0.33

BChl/mprt nmol / mg

BChl / RC mol / mol

pmoi RC / mg mprot,

3.4 25.9

65 126

52 205

mol ATP/ moi BChl min 66 i0

mol ATP / mmol RC. min 4.3 1.3

mol ATP / mg mprot. min 220 260

BChl / cellprot nmol/mg

pmol RC /mg cellprot

nmol ATP / mg cellprot min

cell doubling time (min)

ICM vesicles/cell

ICM area

3 high light low light

2.14 18.3

30 145

140 180

190 190

42 325

chemostat 4

NADH-DH U/mg plot

NADphored U/ mg prot

phoautN2

2.41

5.3

phohet

1.48

1.2

2 high light low light

cyt b566

(#m 2) 0.4 2.5

High light" 6 x 300 W peripheral lamps, 1 x 200 W central lamp; low light: ! x 40 W central lamp; experimental conditions for turbidostat in Reidl et al. (1983, 1985). Abbreviations: BChl-bacteriochlorophyll a; I C M - intracytoplasmic membrane; cell prot-cell protein; mprot-membrane protein; cyt-cytochrome; mol ATP/-photophosphorylation measured as mol ATP synthesized per mmol RC or per mol BChl or per mg membrane protein per min; RC-reaction center; UQ-ubiquinone; Chemostat: phoautN2photoantotrophic, N2-fixing; phohet,light, anaerobic, malate, NI-14+; NAD-phored-NAD + photoreduction, H2 e--donor; NADH-DH-NADH-ferricyaaide oxidoreductase. Data from: 1: Garcia et al. 0987); 2 + 3; Reidl et al. 0985); 4: S. Herter (unpublished).

Table 2. Bacteriochlorophyll content of membranes from Rhodobacter capsulatus 37b4, precultivated at 400 mm Hg ( = 53.3 kPa) oxygen tension in the dark at 30 ° C. The formation of the photosynthetic apparatus was induced at time 0 by lowering the oxygen tension to 1-2 mm Hg ( 200 Pa) in the dark Time (min) after induction 0 30 60 90 130 150

nmol BChl / mg membrane protein

pmol RC BChl / mg membrane protein

mol total BChl / mol RC BChl

0.14 0.15 0.50 i. 13 2.35 2.80

9.3 9.5 25.8 32.0 52.6 53.4

14.6 15.8 19.5 35.4 44.7 52.5

Abbreviations: BChl-bacteriochlorophyll a; RC-rea¢tion center. See Figure I. From Schumacher and Drews (1978)

336 hvrA regB senC regAI hvrB ORF5 ahcY ORF7

U P Io,,, I+

DP ~1 /I.

(::DDD

oxygen Ij.._._~ ~ t l l light

J

'"'''"'""

"'

•

,

i

l.

I

L_

"U

' ....

"

bch

I I P-bch "~

~

ca,

,bch,

crt

,t--bch--u-puf.-t

,

,

puc

~-

off 469 Figure 3. Photosynthetic gene cluster of Rhodobacter capsulatus and regulation of gene expression. Transcription of the puf, puh, and puc operons under the influence of low oxygen partial pressure is positively regulated by the two-component RegB/RegA system. Low light intensity enhancesd transcription ofpuh and pufoperons by HvrA. Crtl (Orf469) stimulates transcription of genes for pigment synthesis. Genes, coding for: bch, bacteriochlorophyll synthesis; crt, carotenoid synthesis; puf, LH I a,fl (AB) proteins, reaction center LM proteins, regulatory proteins Q and X; puh, reaction center subunit H; puc, LH II proteins BAE (~c~7), regulatory protein C. Adapted from drawings of Beatty (1995) and Bauer (1995).

tion of the expression of the respective genes (Klug et al. 1985).

The discovery and analysis of light-harvesting and reaction center complexes Two different approaches led to the important discovery that BChl and carotenoids are bound to specific membrane proteins that are synthesized synchronously with the pigments. In a kinetic study, it was shown that after induction by lowering the oxygen tension, BChl and 'photosynthetic' - polypeptides were incorporated into the cytoplasmic membrane fraction first, and in a second phase of morphogenesis, vesicles formed by invagination became enriched in BChl and thylakoid-specific proteins. It was concluded that ICM and cytoplasmic membrane represent modifications of a dynamic membrane system and that BChl and specific proteins are inserted coordinately first into the cytoplasmic membrane and then increasingly into the ICM system (Biedermann and Drews 1968; Oelze et al. 1969a,b; Oelze and Drews 1970). The rate of photophosphorylation increased linearly on the basis of membrane protein, but decreased on the basis of BChl concentration (Drews et al. 1969; Lampe and Drews 1972) since two forms of BChl, the light-harvesting (LH) and the reaction center BChl are in the chromatophores (Clayton 1962, 1963, 1966). LH BChl

increased relatively to RC BChl (Schumacher and Drews 1978, 1979). Direct proof that the photosynthetic pigments are associated with specific proteins derived from isolation and spectroscopic studies of membrane subparticles. Clayton (1963, 1966) showed that the light-harvesting BChl can be destroyed by treatment with iridic chloride or bleaching by strong light without harming the photochemical by active P870. In several laboratories, subchromatophore (light-harvesting and reaction center) particles were isolated from detergent-treated membranes by sucrose-density gradient centrifugation (Bril 1960; Garcia et al. 1966; 1968, Reed 1969). The purification and characterization of reaction center preparations were optimized (Clayton and Wang 1971), and the composition of proteins and cofactors were determined (Straley et al. 1973; Feher and Okamura 1978). The LH complexes isolated at that time were not very well characterized because of insufficient purification and a high sensitivity of LH-BChl to detergents, salts, and light (see Clayton 1962, 1963). The spectral forms B800, B820, B850, B870-890 and B1020 were found in several sulfur and non-sulfur purple bacteria associated with proteins (Clayton and Clayton 1972; Clayton and Haselkorn 1972; Fraker and Kaplan 1972; Nieth and Drews 1974, 1975; Oelze and Pahlke 1976; Thornber et al. 1978; Cogdell and Thornber 1980). At the end of the 1970s and beginning of 1980s, methods of isolation of highly purified LH

337 Table 3. Bacteriochlorophyll content of membranes from cells of Rhodobacter capsulatus 37b4, precultivated at 53 kPa 02 in the dark at 30°C. At time 0, the culture was shifted to an oxygen tension of 70 Pa. The cell did not divide, but synthesized bacteriochlorophyll (BChl) and proteins of reaction center (RC) and light-harvesting (LH) complex I. LH H complexes are formed only in traces. The size of the photosynthetic unit (total BChl / RC) did not increase beyond 35, and the dominating absorption peak is at 895 nm (LH I) at 77 K. From Schumacher and Drews (1978) Time (min) after induction

Cell protein mg / ml

nmol BChl / mg protein

nmol RC BChl/ mg protein

Total BChl (mol) per mol RC BChl

30 60 90 120 150 180 210

0.526 0.529 0.552 0.552 0.600 0.600 0.600

0.66 1.68 2.78 5.57 7.95 8.69 8.61

0.03 0.06 0.09 0.15 0.23 0.26 0.26

24.3 29.3 31.2 37.7 34.2 32.7 32.5

complexes and analyses of their amino acid sequence were developed. During the 1980s, the complete amino acid sequences of the BChl-binding proteins cz and/~ from the B870 (LH I) core complex and the B800-850 (LH II) variable complex of numerous species were determined, particularly in the laboratory of Herbert Zuber (reviewed in Drews 1985; Tadros and Drews 1990; Zuber 1990) and the exact stoichiometry of the pigments and proteins and their putative localization in the membrane were determined. It was striking that in all analyzed LH-complexes from purple bacteria, two or three BChl and one or two carotenoid molecules are bound to two very small (mol. mass 5 to 6 kDa) polypeptides that span the membrane only once. The central hydrophobic domain and the N-terminal and the C-terminal regions contain highly conserved amino acid positions. All complexes are present as oligomers of the heterodimer. This was determined by various methods of molecular weight analysis of the native complex. Our work in Freiburg was directed on the LH complexes of Rba. capsulatus and Rps. palustris. The LH II complex of Rba. capsulatus was isolated, and the composition, amino acid sequence of polypeptides and the oligomeric structure (mol. mass 180 kDa) were determined (Feick and Drews 1978, 1979; Shiozawa et al. 1980, 1982; Tadros et al. 1983, 1985). We were immediately interested to know how the LH complexes are located in the membrane and studied the topography of several LH-proteins in the membrane. In all investigated species, the N-terminal regions of the a and/3 polypeptides were found to be exposed on the cytoplasmic surface of the membrane after insertion into the membrane, and the C-terminal

domains were found to point toward the periplasm (Tadros et al. 1987). After insertion into the membrane the LHI polypeptide ofRba, capsulatus is phosphorylated at position Ser-2 (Brand et al. 1995). The LH II complex of Rba. capsulatus, but not that of Rba. sphaeroides, contained a third (7) non-pigmentbinding protein that stabilizes the B800 component (Feick and Drews 1979; Tichy et al. 1991). We were very excited when we obtained crystals of the LH II complexes of Rba. capsulatus and of Rps. palustris and crystals of the reaction center-LH I core complex from Rps. palustris. The orientation of the Qx and the Qy transitions of BChl relative to the crystal axis was determined by spectroscopy with polarized light (Welte et al. 1985; Wacker et al. 1986; Mantele et al. 1988). Thomas Wacker in Wolfram Welte's group worked diligently to obtain good crystals for high resolution X-ray spectroscopy. Unfortunately, the attempts were unsuccessful, and we gave up this otherwise successful cooperation after many years of frustrating work. We all were very happy when finally Richard Cogdell's group solved the structure of the LH II complex from Rps. acidophila at 2.8 A (McDermott et al. 1995), and an 8.5 A projection map of 2-D crystals from the LHI complex of Rsp. rubrum was obtained (Karrasch et al. 1995). Both studies confirmed the oligomeric state of the LH complexes. Recent electron microscopical investigations of 2-D crystals from several purple bacteria seem to confirm that the LH I complex, which surrounds the RC, consists of 12 heterodimers (a3), while the LH II complex contains eight or nine subunits (Boonstra et al. 1994; Oling et al. 1996).

338 The powerful method of site-directed mutagenesis introduced in the 1980s in combination with spectroscopic methods (Raman and absorption and excitation spectroscopy) allowed the determination of amino acid positions important for binding of pigments, e.g. the Ala-X-X-X-His domain for BChl binding or Trp8 in LH I as part of the carotenoid binding motif. Several mutants were constructed that were inhibited in assembly or showed blue-shifted complexes (Hunter 1995). An important step forward in the research on primary processes of photosynthesis was the high-resolution Xray spectroscopy and the resulting three-dimensional structure of the reaction centers of Rhodopseudomonas viridis (Deisenhofer et al. 1984, 1985, Michel et al. 1985, 1986) and ofRhodopseudomonas (Rhodobacter) sphaeroides (Allen et al. 1988; Komiya et al. 1988).

The chlorosome story The photosynthetic green sulfur bacteria were known as strictly anaerobic photolithotrophs (van Niel 1932) that contain traces of BChl a and large amounts of Chlorobium chlorophyll absorbing at 650 or 660 nm. In several strains of Chlorobium thiosulfatophilum and Clb. limicola, a completely new structure in the form of oblong vesicles (30--40 nm wide and 100-150 nm long) attached on the cytoplasmic side to the cytoplasmic membrane with a high content of chlorobium chlorophyll (240 #g/mg protein) was detected (CohenBazire et al. 1964). These green sulfur bacteria contain bacteriochlorophyil (formerly known as chlorobium chlorophyll) c, d, or e as major light-harvesting BChl and small amounts of BChl a (Jensen et al. 1964; Gloe et al. 1975). Andrew Staehelin (from Boulder, Colorado) and Clinton Fuller (from Amherst Massachusetts) spent a sabbatical leave in Freiburg, and we decided to study the supramolecular organization of the chlorobium vesicles in freeze-fractured cells of Chlorobium limicola and Chloroflexus aurantiacus (Staehelin et al. 1978, 1980). The structures were named 'chlorosomes' in analogy to the phycobilisomes in cyanobacteria and red algae. Chlorosomes and phycobilisomes are light-harvesting organelles attached to the surface of the photosynthetic membrane, but differ fundamentally from each other in structure and composition. In the chlorosome core, rod-shaped elements were observed that presumably consist of aggregated BChl c molecules stacked by OH""O=C bonds between chlorine pairs and by electrostatic interaction (Staehelin et al. 1978, 1980; Holzwarth and Schaffn-

er 1994). Spectral shifts resulting from aggregation of BChl molecules in organic solvents were at first detected and investigated by Joe Katz. The rod elements are embedded in lipids and limited to the cytoplasm by a lipid monolayer interspersed with proteins. A crystalline baseplate connects the chlorosome to the cytoplasmic membrane. The attachment region of the chlorosomes to the cytoplasmic membrane is filled with large intramembrane particles that may be the light-harvesting BChl-a-reaction-center complexes (Staehelin et al. 1978, 1980). This model is still current and it initiated numerous investigations on the chlorosomal components and the energy transfer within the chlorosomes and to the reaction center (reviewed in Amesz 1991; Blankenship et al. 1995; Feiler and Hauska 1995). The chlorosomes of Chlorobium spec. are large and suitable for structural and spectroscopic studies; the chlorosomes of Chloroflexus are smaller, but suitable for studies on the morphopesis of chlorosomes because of the ability of Chloroflexus to grow chemotrophically in presence of oxygen, under which conditions no BChl and no chlorosomes are present, or phototrophically, i.e. under anoxic conditions in light. The BChl c content and the size of chlorosomes are regulated in correlation to oxygen tension and light intensity (Golecki and Oelze 1987; Oelze 1992; Foidl et al. 1994).

Bioenergetics and development Photophosphorylation in anaerobic cultures of purple bacteria is coupled to a cyclic light-driven electron transport (Nozaki et al. 1963), which is independent of a constant input and output of electrons. However, the rate of photophosphorylation is affected by the redox potential of the experimental system (Drews 1962, 1964). The influence of culture conditions on the enzymatic activities of the respiratory and photosynthetic electron transport was investigated. The rate of photophosphorylation, the activities of NADH dehydrogenase and succinate dehydrogenase, and respiration were found to be higher in high-light-grown cells than in low-light-grown cells on the basis of membrane protein (Schumacher and Drews 1979). In experiments with turbidostat cultures of Rba. capsulatus grown under high light intensity (1400 W/m 2) the BChl content, the number of intracytoplasmic membrane vesicles, the size of the photosynthetic unit (mol lightharvesting BChl/mol reaction center) and the reaction center content were quantified and found to be much

339 lower than in cells grown at 40 W / m 2. However, the photophosphorylation rate per reaction center under saturating light conditions was 7.7-fold higher in highlight-grown cells than in low-light-grown cells. Saturation curves obtained from the two adaptation stages of cells indicated not only a variation of the size and composition of the antennae, but also a change in the affinity of the photosynthetic system to light (Reidl et al. 1983, 1985; see Table 1). Fusion of membrane vesicles with liposomes resulted in a fivefold increase of the apparent Km for light, indicating an energy dissipation by dilution of the components of the photosynthetic unit (Garcia et al. 1985). Under low-light intensity, the amount of the peripheral LH II (B800850) complex and of reaction center per cell increased. Cells adapted to the respective growth conditions grew with the same cell doubling time (Table 1). A mutant lacking the LH II complexes (B80(O850) cannot fully adapt to low light intensities; therefore, the cell doubling time increased. The ratio of ATP synthase to reaction center was altered. The apparent Km for light was three to four times lower under low-lightconditions in wild-type cells than in cells deficient in the LH II complex. The experiments indicated that wild-type cells of Rba. capsulatus are more flexible at adapting to different light conditions than mutant strains because they can vary the size and the amount of photosynthetic units per cell. Their lower Km might be an advantage over competitors in dim light and may explain the effort to synthesize an extensive intracytoplasmic membrane system (Reidl et al. 1985). Cells adapted to high-or low-light intensities differed in the amount of photosynthetic units per cell and also significantly in their molar ratios of ubiquinone and band c-type cytochromes, which increase three-to fivefold in high-light-grown cells (Table 1). From these data and kinetic data, it was concluded that the cyclic electron flow under saturating light intensities is faster in high-light-grown cells than in low-light-grown cells (Garcia et al. 1987). These and other results of comparative studies showed that membrane differentiation includes numerous biosynthetic processes that must be regulated coordinately by a global regulatory network. The great break-through in understanding the coupling mechanism between the light-driven or respiratory electron transport and the ATP synthesis or energy-dependent transport of solutes was obtained by the chemiosmotic theory of Peter Mitchell (1966). Since the beginning of studies on regulation of cell differentiation, the nature of the sensor system(s) for oxygen tension or light intensity, was under con-

sideration. It was discussed that the regulation of BChl synthesis and formation of the photosynthetic apparatus are under the control of the energy charge [ = (ATP + 0.5 ADP)/(ATP + ADP + AMP)] and/or the ratio NAD(P)+/NAD(P)H or the redox state of a component of the electron transport chain (Cohen-Bazire et al. 1957; SchSn 1971; Zilinsky et al. 1971; Marrs and Gest 1973). However, the synthesis of the photosynthetic apparatus is independent from the growth rate, which influences the above mentioned ratios of cofactors. Oxygen tension and light intensity seem to control the membrane differentiation via independent effector molecules and a signal chain that regulates transcriptional and posttranscriptional processes. As shown before, the differentiation of the membrane system in Rba. capsulatus comprises most components of the photosynthetic and of the respiratory apparatuses. In addition to the pigment-protein complexes and electron carriers mentioned above, the amount and activity of cytochrome oxidase increase after a shift from phototrophic to chemotrophic (aerobic dark) growth conditions (Hiidig et al. 1987). Similar results were obtained with Rps. palustris (King and Drews 1975, 1976; Firsow and Drews 1977). Lowering of oxygen tension in chemotrophic cultures or a shift from chemotrophic to phototrophic growth conditions induces the biosynthesis of pigments and the increase of the membrane area by invaginations of the cytoplasmic membrane (Drews and Giesbrecht 1963). It was proposed that invagination zones are identical with membrane domains where constituents of the photosynthetic apparatus (RC and LH polypeptides) are assembled (Oelze and Drews 1969; Oelze et al. 1969a,b; Golecki and Oelze 1975; Drews 1978; Kaplan 1978; Hunter et al. 1979, 1988, Niederman et al. 1979; Dierstein et al. 1981; Drews and Oelze 1981; Ohad and Drews 1982; Drews and Golecki 1995). The H subunit of RC is present in aerobically grown cells and might be a targeting site for the assembly of the RC (Sockett et al. 1989). The process might be similar to the assembly and budding of enveloped viruses at the host plasma membrane, where virus-specific proteins are incorporated, dislodge the host-specific proteins, and serve as crystallization centers for morphogenetic processes. It was speculated that the incorporation of photosynthetic proteins and of phospholipids into the cytoplasmic membrane not only enlarges the membrane, but initiates specifically the formation of intracytoplasmic membranes.

340

Molecular genetic approach to study development of anoxygenic photosynthetic bacteria At the end of the seventies a detailed picture of celland membrane differentiation was known. However, the mechanisms of regulation and coordination of the involved biosynthetic and morphogenetic processes remained unknown. To solve these problems, techniques of molecular genetics have been introduced. The preparation of mutants defective in formation of photosynthetic pigment or protein synthesis (Sistrom and Clayton 1964; Lascelles 1966; Lascelles and Altshuler 1967; Drews et al. 1971; Weaver 1971) and the discovery of the gene transfer agent for Rba. capsulatus by Barry Marrs (1974) was the beginning of molecular biological studies on phototrophic bacteria. One of the first regulatory mutants that produced BChl under oxic conditions was detected by Lascelles and Wertlieb (1971). The gene-transfer agent was used for mapping small photosynthetic gene regions (Yen and Marrs 1976) and for reconstitution of mutant strains (Wall et al. 1975; Drews et al. 1976). The transfer of chromosomal genes with promiscuous plasmids became the method of choice for cloning and transferring genes (Sistrom 1977). Barry Marrs was the first to isolate and characterize the photosynthetic gene cluster of about 46 kb from Rba. capsulatus (Marrs 1981). The DNA sequence of this cluster and Tn5 insertion mutations showed that the genes encoding the enzymes of BChl and carotenoid synthesis, the proteins of the reaction center and of the LH I complex, together with regulatory genes, were localized in this DNA region (Figure 3, Youvan et al. 1984; Zsebo and Hearst 1984). The sequence and arrangement of these genes seems to be conserved, as shown by studies with the photosynthetic bacteria Rps. viridis, Rubrivivax gelatinosus, Rba. capsulatus, Rba. sphaeroides, Rsp. rubrum and Rsp. centenum (Belanger et al. 1988, Donohue et al. 1988; Nagashima et al. 1994; Wiessner et al. 1990; Yildiz et al. 1992).

The global regulatory network for expression of photosynthetic genes After detailed studies on sequences and expression of many 'photosynthetic' genes the first regulatory elements have been analyzed. It was shown that the photosynthetic gene clusters are organized in large superoperons, i.e. several operons are co-transcribed (Figure 3, Young et al. 1989; Bauer et al. 1991; Wellington and

Beatty 1991; Beatty 1995). Linking of genes in superoperons has consequences for mRNA production and translation. In addition to control of transcription initiation, the mRNA life-time is under control (Klug et al. 1987). There is agreement of several laboratories that expression of bch and crt genes is repressed approximately two-to fivefold when cells are grown under high-oxygen versus low-oxygen partial pressure. The LH and RC structural genes in the pufandpuc operons are expressed to a much higher level when the oxygen tension is strongly reduced, and these genes are more highly regulated (up to 100-fold) (Bauer et al. 1988). The results of the investigations in Rba. capsulatus and Rba. sphaeroides have shown that besides transand cis-active elements, which affect the transcription of photosynthetic genes (Figure 3), posttranscriptional processes are active. The co-regulation of many genes by the same stimulus suggested that a global regulatory network of the type of a modulon is present, i.e. the coordinated regulation of blocs of pigment and cofactor biosynthetic pathways, of synthesis of pigmentbinding polypeptides, of elements of the regulatory cascade and of helper proteins. We are at present far away from understanding all parts of the regulatory network. But it is fascinating to learn that these finetuned regulatory systems have developed in prokaryotes during a long evolution and that the principles of these systems have been adapted and completed in eukaryotes. The interested reader is referred to recent review articles on that topic (Bauer 1995; Beatty 1995; Klug 1995; Inoue et al. 1995; Erasco and Kaplan 1995; Gomelsky and Kaplan 1995; Sabaty and Kaplan 1996).

The coordinated synthesis and assembly of photosynthetic gene products Mutation of bch genes inhibits not only BChl synthesis but also the stable insertion of pigment-binding proteins into the membrane (Dierstein 1983; Klug et al. 1986; Brand 1995). Deletion of genes encoding pigment-binding proteins (A puf, puc) or inhibition of protein synthesis reduces the amounts of BChl in the cells (Drews 1965; Klug et al. 1987; Klug and Cohen 1988). BChl biosynthesis is regulated at various levels. Changes in oxygen partial pressure affect the transcription of key enzymes of tetrapyrrole synthesis, e.g. the transcription rate of the gene hemA, encoding the first enzyme of tetrapyrrole synthesis, 6-aminolevulinate synthase, is regulated two- to threefold (Hornberger et al. 1990, 1991). Similar changes have been described

341 for genes of other enzymes of BChl synthesis. High oxygen tension prevents the conversion of protoporphyrin to Mg-protoporphyrin monomethyl ester (Biel 1995). The key enzymes at the branching point of the Mg- and the Fe-pathway of tetrapyrrole synthesis are under feed-back control. The regulation of BChl synthesis has been descibed by Lascelles (1978) and Biel (1995). The role of PufQ, which was proposed to mediate the incorporation of BChl into the LH proteins, and the influence of heme and cytochrome c in the regulation of the tetrapyrrole pathway remains to be explored. Light intensity seems to affect the stability of BChl. Increasing light intensity accelerates the degradation of BChl (Biel 1995). In wild-type cells, that are adapted to synthesize the photosynthetic apparatus, the amounts of free precursors of BChl are very low (Beck and Drews 1982), indicating that the coordinated regulation of the cellular levels of pigments and pigment-binding proteins is fine-tuned. This mechanism has to be explored. Carotenoids have a dual function in photosynthesis: they are efficient light-harvesting molecules, and they protect the photosynthetic apparatus from photooxidative damage. Photosynthetic bacteria depleted of carotenoids by inhibitors or mutation are killed in the presence of oxygen and light (Griffiths et al. 1955), but they can grow under strictly anoxic conditions. In addition to these important functions, carotenoids seem to be essential for the structure and function of the LH II (B800-850) complex. This was indicated by the observation that mutants lacking carotenoids synthesize functional RC and LH I complexes, but do not synthesize the LH II complex (Kaufmann et al. 1984; Zsebo and Hearst 1984). Mutation of the crtl gene, encoding phytoene desaturase, inhibits completely the formation of the LH II complex. In the crtl-negative mutant of Rba. sphaeroides, the mRNAs for LH Icz and/5 and the polypeptides are synthesized, but the proteins disappear from the membrane within 10 min (Lang and Hunter 1994). In the crtl-blocked mutant of Rba. capsulatus, however, the levels of the pucBA mRNA and of the pucDE mRNA were about 25-fold and 10-fold lower than that in the wild-type cells, respectively (Oberl6 et al. 1990), and the insertion of the polypeptides in the membrane was strongly reduced. The LH Ilcz polypeptide was stably incorporated, while LH I1/3 and 7 polypeptides were not detectable or disappeared quickly (Brand 1995). The carotenoids of the LH II complex sense the membrane potential, indicated by the electrochromic bandshift which is measured by the relationship between

the carotenoid absorption change and the membrane potential. There seems to be a large permanent field in the surrounding of the reactive carotenoids. An exchange of charged amino acids in the vicinity of the carotenoids (/SArg 29 ---r Glu) changed the permanent field near the carotenoids (Hunter 1995). The X-ray structure of the LH II complex ofRps, acidophila showed that the carotenoid molecules connect the B800 and the B850 BChl molecules ( McDermott et al. 1995). The functional role of carotenoids for the LH II complex is supported by these data, but the questions why carotenoids are essential for formation and stability of the LH II complex and why there is a pleiotropic effect on transcription ofpuc genes of Rba. capsulatus remains unanswered. A significant role of carotenoids in maintaining the native oligomeric structure of the LH II complex was concluded from Fourier transform Raman and CD spectroscopy. Extraction of carotenoids resulted in dissociation of the B800 BChl and loss of the stability of LH II (Zurdo et al. 1995). The puc operon, encoding the proteins of the LH II complex, 1is located outside of the photosynthetic gene cluster (Youvan et al. 1984). Besides the promoter upstream region the pucC gene product is essential for expression of the puc operon and the formation of LH II (Tichy et al. 1989, 1991). It was interesting to learn that PucC which is located in the midst of the puc operon is synthesized only in trace amounts and was detected on SDS polyacrylamide gels only ifpucC was cloned behind a strong promoter and an effective Shine-Dalgarno sequence (C. Kortlticke and G. Drews unpublished). Although the puc operon is under the general oxygen and light control, its regulation is relatively independent from that of the pufoperon, encoding RC and LH I genes (Klug et al. 1985; Bauer 1995; Lee and Kaplan 1995; Sabaty and Kaplan 1996).

Morphological types of intracytoplasmic membranes The ICM consists of characteristic, species-specific patterns of vesicles, tubes, and stacked or unstacked thylakoid-like membranes. This observation raised the idea that the major integral proteins have a morphogenetic effect on the ICM formation. LH II mutants of Rba. sphaeroides defective in the LH II complex were described as containing long tubes spanning the cell in the longitudinal axis (Lommen and Takemoto 1978; Hunter et al. 1988; Kiley et al. 1988; Golecki et al. 1989, 1991). These tubes, which are present in addi-

342 tion to normal-sized ICM vesicles, contained numerous intramembrane particles, indicating that they are not myelin-like structures. Recent studies with Rba. capsulatus mutants in which the puc operon was completely deleted showed vesicles of irregular size, but no tubules (J.R. Golecki and G. Drews, unpublished). These observations indicate that major integral membrane proteins of the photosynthetic apparatus affect the structure of the ICM, but a defined morphogenetic protein has not been detected (Drews and Golecki 1995).

Lateral organization of the photosynthetic membrane Membranes are regarded as two-dimensional solutions of oriented lipids and proteins. The lateral mobility of proteins is dependent on numerous factors, such as temperature, protein/lipid ratio, fatty acid composition, and special interactions between proteins and between proteins and lipids. Recent studies with isolated functional complexes, electron microscopic investigations of freeze-fractured membranes, image-processed pictures of membranes and reconstituted complexes in lipid films, and high-resolution X-ray studies and spectroscopic investigations of crystallized functional complexes have presented convincing evidence that in the photosynthetic membrane, supercomplexes exist at least temporarily: about 12-16 subunits ofLH I surround the RC and form the core complex (Karrasch et al. 1995). Functional analysis indicated that RCs, cyt c2 and cyt bcl complexes form supercomplexes in distinct membrane domains (Vermeglio et al. 1995); chlorosomes filled with aggregates of BChl c are anchored with a crystalline baseplate to the cytoplasmic membrane and may form supercomplexes with the underlying membrane-bound BChl a light-harvesting complexes, and the RCs, visualized by larger intramembrahe particles (St~ihelin et al. 1978, 1980; Blankenship et al. 1995). These large supercomplexes restrict lateral mobility. Although cytoplasmic and intracytoplasmic membrane form a continuum, isolated ICM and CM fractions appear at different positions in a sucrose gradient after equilibrium density centrifugation, indicating different densities. These fractions contained different enzymatic activities and different concentrations of pigments, cofactors and proteins (Garcia and Drews 1980). The formation of supercomplexes predicts that not only are the polypeptides of a functional complex linked together by non-covalent bonds, but that weak

forces keep light-harvesting and reaction center complexes and RC and cyt bcl complexes together. Supercomplexes exist only transiently and fall apart if electrostatic or hydrophobic interactions are changed. The kinetics of association and dissociation of supercomplexes remains to be determined and is only known for the interaction between RC and cytochrome c2,, and cytochrome c2 and cytochrome bcl complex interaction (Caffrey et al. 1992; Guner et al. 1993). The formation of supercomplexes and the insertion and assembly of new functional units in specific regions of the growing membrane results in a differentiation of the membrane system. All these results of many studies have shown that biomembranes, especially those of electron transport, are not lipid lakes where proteins are randomly distributed by lateral diffusion, but organized and differentiated mini-compartments. Local differentiation in a membrane has also been shown in Caulobacter (swarmer versus stalked pole, Gober and Marques 1995). These and other examples revealed that mechanisms of membrane differentiation have developed in prokaryotes, and their investigation may help to understand the formation of the more complex membrane systems of eukaryotic cells.

The process of assembly of light-harvesting complex I During the last decade, much progress was achieved in the field of protein import and export in prokaryotes and in mitochondria and chloroplasts of eukaryotes (von Heijne 1994). However, our knowledge on insertion and assembly of polypeptides in membranes is limited. In the course of our studies on membrane differentiation we became interested in the mechanism of assembly of the photosynthetic apparatus and began studies on the formation of the LH I complex in Rba. capsulatus. As described earlier, this LH I or B870 complex is an oligomeric form of the B820 subunit, which consists of one polypeptide (mol. wt. in Rba. capsulatus 6588), one polypeptide (mol. wt. in Rba. capsulatus 5341), 2 mol of BChl, and 1 mol carotenoid (Drews 1985). In Rsp. rubrum, 16 B820 subunits form a ring-like structure that surrounds the reaction center (Karrasch et al. 1995). The B870 complex was isolated from Rsp. rubrum and other purple bacteria and reversibly dissociated by detergents into the B820 monomeric subunit or into the pigment and protein components and reassociated to the oligomeric form (Ghosh et al. 1988 Meckenstock et al. 1992; Loach

343 and Parkes-Loach 1995; Meadows et al. 1995). It was shown that the hydrophobic c~-helical central region of the a and/3 polypeptides with their specific binding sites for pigments and the N-terminal regions of the polypeptides are of importance for the formation of B820 and B870 spectral forms. Truncation and modification of the polypeptides in the N-terminal region to a small extent did not diminish the formation of LH I and have provided minimal requirements for the formation of the complex (Meadow et al. 1995). The Mg -atom, the carbonyl group at C3, and the carbmethoxy group at C13 of the tetrapyrrole ring of BChl a are necessary for the molecule to fit during assembly in the protein scaffold (Loach and Parkes-Loach 1995). These results of in vitro experiments present important informations on the interaction of polypeptides and pigments during the assembly of a functional LH I complex. However, the in vitro experimental conditions do not correspond to the in vivo conditions in the cell because the lipid double layer of the membrane with its proteinaceous components is replaced by a detergent micelle, and the process of targeting and insertion of the nascent proteins and pigment precursors in the membrane is not included in the experimental system. Membrane-bound complexes are in vivo never formed de novo. The in vivo-assembly is dependent on pre-existent structures and the interplay of numerous gene products and participation of the cellular organization (Harold 1995). To explore the in vivo process of assembly the following experimental approaches were developed: i) a cell-free transcription-translation system according Troschel and Mtiiler (1990) was established (Meryandini and Drews 1996) and (ii) the N-terminal regions of the LH I polypeptides were modified by site-directed mutagenesis and the incorporation of the mutated proteins observed by pulse-chase experiments (Dtirge et al. 1990). Transcripts of the genes pufBA, pufB, or pufA, encoding the polypeptides/3and a of Rba. capsulatus, were translated in a cell-free system of Rba. capsulatus and the insertion of the 35S_methionine.labeled proteins into the membrane fraction and the assembly of the LH I complex was investigated. Stably and correctly incorporated polypeptides were, in contrast to loosely attached and incorrectly incorporated proteins, not extractable by 6 M urea. The highest rate of stable incorporation of LH Ia/3 into the membrane was obtained with membranes from the wild-type strain grown under chemotrophic conditions. Membranes from phototrophically grown cells that are full of photosynthetic pigment complexes or membranes from

cells defective in biosynthesis of pigment-proteins are less effective in stable incorporation of the LH proteins. In contrast to the in vitro experiments, single polypeptides, a or/3, are not stably inserted and do not form any LH -complex in the membrane. The stably inserted polypeptides LH Ia/3 bound BChl are shown by its absorption spectrum (Meryandini and Drews 1996). Since the LH I polypeptides are very hydrophobic, it was not surprising that the nascent polypeptides were supported and protected from misfolding by chaperones. The translation of both polypeptides was strongly reduced if the chaperone DnaK was removed from the cell-free extract. GroEL supported the targeting to the membrane and the stable insertion. GroEL interacted with LH I a and/3 before membrane targeting, as shown by immunological means. Proteins bound to the surface of the membrane and extractable by a low-salt buffer supported the stable insertion of the LH I polypeptides (Meryandini and Drews 1996). The integration of pigment-binding proteins was dependent on the electrochemical gradient of protons (Dierstein and Drews 1986). The NH2-terminal regions of the LH I ~/3 polypeptides, which are exposed on the cytoplasmic side of the membrane after insertion, stabilized the B820 subunit and the oligomeric complex by interaction. This seems to be true not only for the LH I complex, but also for the LH II complex (Richter and Drews 1991; Meadows et al. 1995; McDermott et al. 1995). The N-terminal regions of a and/3 participate presumably in the targeting, formation of the heterodimer a/3, and the assembly process. Small modifications of the amino acid sequence of LH I [exchange of single conserved amino acyl residues (e.g. aI Trp-8--+Ala, aI Pro-13--+Lys) deletions, insertions] are sufficient to inhibit completely the stable incorporation of a and of/3 polypeptides and the formation of the LH I complex, which supports the idea that the conformation of the N-terminal regions is important for the formation of the heterodimer (Stiehle et al. 1990; Richter and Drews 1991; Richter et al. 1991, 1992). The contrary observation that truncated LH I~/3 form LH I complexes in vitro may result from the experimental conditions (Meadows et al. 1995). The recent results from in in vivo systems show that the pigment-binding polypeptides of the LH-complexes are guided from translation up to insertion and assembly in the membrane, and that the efficiency of this process relies on many factors, including chaperones and the composition and physiological state of the membrane. Exchanges of single

344 amino acyl residues influence also the spectral properties of LH-complexes (Hunter 1988, 1995).

The retrospect of 45 years of the study of developmental biology of the anoxygenic photosynthetic apparatus and the outlook Photosynthetic bacteria have been known for more than one century (Engelmann 1888; Esmarch 1887; Molisch 1907). During the past forty years, our knowledge about these organisms has enormously increased. I have been very happy not only to have seen the immense progress during this period but also to have experienced and to have participated in that process, to have met and to remember most of the persons active in the field and to have seen how microbiologists, plant physiologists, physicists, and biochemists have learned to cooperate and to speak the same scientific language. An impression of the scientific atmosphere in that time is mediated by the reports of contemporaries (van Niel 1967; Stanier 1980; Kaplan and Robinson 1982; Kamen 1986; Gest 1994). The discovery of the different facettes of the metabolism of purple and green bacteria, i.e. photoautotrophy and photoheterotrophy and chemoautotrophy and chemoheterotrophy and the isolation of pure cultures of phototrophic bacteria and cyanobacteria were important prerequisites for the success during the past 40 years. Since the beginning of the 1950s, when the basic mechanism of anoxygenic photosynthesis was detected, much has been learned. In the history of photosynthesis research, anoxygenic photosynthetic bacteria appeared at the front relatively late. The golden age of the research on photosynthetic bacteria up to the fifties has different roots (Huzisige and Ke 1993). The first step during the 1950s was the visualization of intracytoplasmic membranes by electron microscopy, the demonstration of BChl and photophosphorylation in isolated chromatophores of photosynthetic bacteria and the demonstration that the biosynthesis of bacteriochlorophyll is dependent on low oxygen tension. The discovery of charge separation in the photochemical reaction center by timeresolved spectroscopy, the CO2 fixation by the CalvinBenson-Bassham cycle, the function of quinones and cytochromes, and the formulation of the chemiosmotic theory by Mitchell were the important discoveries in the 1960s. In the 1970s, light-harvesting complexes and reaction centers were isolated and analyzed, and the morphogenesis of the photosynthetic membrane under the control of oxygen tension and light intensity

was studied. In the 1980s, a new period was opened that can be characterized by: (i) high-resolution X-ray analysis of the atomic structure of the photochemical bacterial reaction center; (ii) measurements of primary electron transport in purple and green bacteria in the picosecond range; (iii) introduction of methods of molecular genetics to transfer genes and to determine the DNA sequence of the photosynthetic gene cluster ofRba, capsulatus; (iv) analysis of molecular structure and function of the cyt blcl-complex; (v) modeling of structure and function of light-harvesting complexes and detection of the chlorosomes, and (vi) discovery of new photosynthetic bacteria, e.g. Heliobacterium and HeliobaciUus and BChl g. These lines of research are continued in the 1990s. New methods were introduced to study the role of reactive groups in membrane proteins during electron- and proton-translocation. Recently, a new group of bacteria was detected that can synthesize small amounts of BChl a and a photosynthetic apparatus, but these obligate aerobic bacteria are unable to grow photosynthetically under anoxic conditions (Harashima et al. 1989). They grow chemotrophically, and it is open to question whether they can use the photosynthetic apparatus under ecological conditions for photophosphorylation. Are they relicts of evolution or bacteria that are beginning to develop a photosynthetic apparatus? The amino acid sequence of the RC and LH I polypeptides of one member of this group, Roseobacter denitrificans, is similar to that ofRba, capsulatus (Liebetanz et al. 1991). The aerobic, BChl-containing bacteria belong to different taxonomical groups (Yurkov et al. 1994). An open question is why the charge separation in membranes of these bacteria is dependent on oxygen. One step in the BChl synthesis in these bacteria is oxygen-dependent (Porra et al. 1996). Several mechanisms of the global regulatory system for biosynthesis and assembly of the photosynthetic complexes have been discovered. However, the cross-talk between the two-component response regulators, the co-regulation between pigment and protein synthesis, the hierarchy in the cis- and trans-acting regulatory circuits, and the mechanism of formation of intracytoplasmic membranes and membrane-bound complexes remain to be elucidated. The analysis of the promoter and promoter-upstream regions and of regulatory ORFs, e.g. pucC and the ORFs 477 and 469 in Rba. capsulatus, the identification of sigma factors, the sensory systems for oxygen and light intensity (redox control ?), and the regulation of the key enzymes of BChl synthesis are fragmentary.

345 Our present knowledge teach us that the formation of functional complexes in membranes is not a simple self-assembly process of the constituents but is a complex morphogenetic event that is dependent on the preformed cellular organization and regulated by a global regulatory network. Basic mechanisms of cell differentiation and determination of a polar axis have been developed very early during evolution in prokaryotic cells and only refined by eukaryotic multicellular organisms. I believe that research on photosynthetic bacteria, the products of three billion years of evolution, will detect further mechanisms of development and cell differentiation which are of general importance.

Acknowledgements The work of the author was supported by Deutsche Forschungsgemeinschaft, Fonds der Chemischen Industrie and the A.v. Humboldt Foundation. I thank my wife Christiane who accompanied my activities in research and scientific organizations with patience and encouragement. I thank Ms Karen A. Brune for improving the English wording. This article was edited by Govindjee.

References Allen JP, Feher G, Yeates TO, Komiya H and Rees DC (1988) Structure of the reaction center from Rhodobacter sphaeroides. Proc. Natl Acad Sci USA 85:8487-8491 Amesz J (I 99 i ) Green photosynthetic bacteria and heliobacteria. In: Shively JM and Barton LL (eds) Variations in Autotrophic Life, pp 99-119. Academic Press, New York Amon DI 0959) Conversion of light into chemical energy in photosynthesis. Nature (London) 184:lO-21 Amon DI, Allen MB and Whatley FR (1954) Photosynthesis by isolated chloroplasts. Nature (London) 174:394-396 Baccadni-Melandri A, Gest H and San Pietro A (1970) A coupling factor in bacterial photophosphorylation. J Biol Chem 245: 12241226 Bauer CE (1995) Regulation of photosynthesis gene expression, ln: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 1221-1234. Kluwer Academic Publishers, Dordrecht Bauer CE, Young DY and Marts BL (1988) Analysis of the Rlmdobacter capsulatus puf operon: Location of the oxygenregulated promoter region and the identification of an additional puf-encoded gene. J Bioi Chem 263:4820-4827 Bauer CE, Buggy JJ, Yang Z and Marrs BL (1991) The superoperonal organization of genes for pigment biosynthesis and reaction center proteins is a conserved feature in Rlu)ckJbacter capsulatus: Analysis of overlapping bchB and puhA transcripts. Mol Gen Genet 228:438 a,a.4

Beatty JT (1995) Organization of Photosynthesis gene transcripts. In: Blankenship RE, Madigan MT and Bauer CE (¢ds) Anoxygenie Photosynthetic Bacteria, pp 1209-1219. Kluwer Academic Publishers, Dordrecht Beck J and Drews G (1982) Tetrapyrrole derivatives shown by fluorescence emission and excitation spectroscopy in ceils of Rba. capsulatus adapting to phototrophic conditions. Z Natufforsch 37c: 199-204 Belanger G, B~rard J, Corriveau P and Gingras G (1988) The structural genes coding for the L and M subunits of R. rubrura photoreaction center. J Biol Chem 263:7632-7638 Biedermann M and Drews G (1968) Trennung der Thylakoidbausteine einiger Athiorhodacea¢ dutch Gelelektrophorese. Arch Mikrobiol 61: 48-58 Biedermann M, Drews G, Marx R and Schr6der J (1967) Der EinfluB des Sanerstoffpartialdruckes und der Antibiotica Actinomycin and Puromycin auf das Wachstum, die Synthese yon Bacteriochlorophyll und die Thylakoid Morphogenes¢ in Dunkelkulturen yon RhodospiriUura rubrura. Arch Mikrobiol 56:133-147 Bid AJ (1995) Genetic analysis and regulation of bacteriochlorophyll biosynthesis. In: Blankenship RE, Madigan MLT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 1125-1134. Kluwer Academic, Publishers Dordrecht Blankenship, RE, Olson JM and Miller M (1995) Antenna complexes from green photosynthetic bacteria. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 399-435. Kluwer Academic Publishers, Dordrecht Boatman ES (1964) Observations on the fine structure of spheroplasts of RluMospirillum rubrum. J Cell Biol 20:297-311 Boonstra AF, Germeroth L and Boekema F_J (1994) Structure of the light-harvesting antenna from Rtmdospirillum nudischianum studied by electron microscopy. Biochim Biophys Acta 1184: 227-234 Brand M (1995) Einflufi yon Pigment Biosynthese und Phosphorylierung auf den Einban und die Assemblierung tier pigmentbindenden Proteine in die Membran yon Rba. capsulatus. PhD thesis, Freiburg Brand M, Garcia AE Pucheu N, Meryandini A, Kerber N, Tadros MH and Drews G (1995) Phosphorylation of the light-harvesting polypeptide LH 1 ofRhodobacter capsulatus at serine after membrane insertion under chemotrophic and phototrophic growth conditions. Biochim Biophys Acta 1231: 169-175 Bril C (1960) Studies on bacterial chromatophores. I. Reversible disturbance of transfer of electronic excitation energy between bacteriochlorophyll types in Chromatium. Biochim Biophys Acta 39:296-303 Bull MJ and Lascelles J (1963) The association of protein synthesis with the formation of pigments in some photosynthetic bacteria. Biochem J 87:15--28 Caffrey MS, Bartsch RG and Cusanovich MA (1992) Study of cytochrome c2-reaction center interaction by site-directed mutagenesis. J B ioi Chem 267:63 i 7-632 I Chailakhyan LM, Glagoleo AN, Glagoleva TN, Murvahidze GV, Potapova'IV and Skulachev VP (1982) Intercellular power transmission along trichomes ofcyanobacteria. Biochim Biophys Acta 679:60-67 Clayton RK (1962) Primary reactions in bacterial photosynthesis. The nature of light-induced absorbance changes in chromatophores; evidence for a special bacteriochlorophyll. Photochem Photobiol 1:201-210 Clayton RK (1963) Towards the isolation of a photochemical reaction center in Rhodopseudomonas sphaeroides. Biochim Biophys Acta 75:312-323

346 Clayton ILK (1966) Spectroscopic analysis of bacteriochlorophylls in vitro and in vivo. Photocbem Photobiol 5:669--677 Clayton RK and Clayton BJ (1972) Relations between pigments and proteins in the photosynthetic membranes of Rps sphaeroides. Biochim Biophys Acta 283:492-504 Clayton RK and Haseikorn R (1972) Protein components of bacterial photosynthetic membranes. J Mol Bio168:97-105 Clayton RK and Wang RT (1971) Photochemical reaction centers from Rps. sphaeroides. Methods Enzymol 23:696-704 Cogdell RJ and Thornber JP (1980) Light-harvesting pigmentprotein complexes of purple photosyntheticbacteria.FEBS Lctt 122:I-8 Cohn F (I866) Uber die Gesetze der Bewegung der mikroskopischen Pflanzen und Tiere unter dem EinfluB des Lichtes.Hcdwigia 5: 161-166 Cohen-Bazirc G (I963) Some observationson the organizationof the photosynthetic apparatus in purple and green bacteria.In: Gcst H, San Pietro A and Vernon LP (cds) BacterialPhotosynthesis, pp 89--I14. The Antioch Press,Yellow Springs,OH Cohen-Bazire G and Kunisawa R (1960) Some observations on the synthesis and function of the photosynthetic apparatus in RhodospiriUum rubrum. Proc Nail Acad Sci USA 46:1543-1553 Coben-Bazirc G and Kunisawa R (1963) Tbe finestructureof Rhodospirillum rubrum. J Cell Biol 16:401--419 Coben-Bazire G, Sistrom WR and StanierRY (I957) Kinetic studies of pigment synthesisby non-sulfurpurple bacteria.J Cell Comp Physiol 49:25-68 Cohen-Bazire G, Pfennig N and Kunisawa R (1964) The fine structure of green bacteria.J Cell Biol 22:207-225 Dcisenhofer J,Epp O, Miki K, Huber R and Michel H (1984) X ray structure analysis of a membrane protein complex. J Mol Biol 180:385-398 Deisenhofer J, Epp O, Mild K, Huber R and Michel H (1985) Slructore of the protein subunits in the photosynthetic reaction centre of Rhodopseudomonas viridis at 3 ]~ resolution. Nature 318:618624 Dierstein R (1983) Biosynthesis of pigment-protein complex polypeptides in bacteriochlorophyll-less mutant cells of Rps. capsu/ata. FEBS Lett 160:281-286 Dierstein R and Drews O (1974) Nilrogen-limited continuous culture of Rps. capsulata growing photosynthetically or heterolrophically at low oxygen tensions. Arch Microbiol 99:117-128 Dierstein R and Drews G (1986) Effect of uncoupler on assembly pathway for pigment-binding protein of bacterial photosynthetic apparatus. J Bacteriol 168:167-172 Dierstein R, Schumacher A and Drews G (1981) On insertion of pigment-associated polypcptides during membrane biogenesis in Rps. capsulata. Arch Microbiol 128:376-383 I)6rge B, Khig G, Gad'on N, Cohen SN and Drews G (1990) Effects on the formation of antenna complex B870 of Rhodobacter capsulatus by exchange of charged amino adds in the N-terminal domain of the a and B pigment-binding proteins.Biochemistry 29:7754-7758 Doi M, Shioi Y, Gad'on N, Golccki JR and Drews G (1991) Spectroscopicalstudieson the light-harvestingcomplex II from darkaerobic and light-anaerobic grown ceils of Rhodobacter sulfidophil~. Biochim Biophys Acta 1058:235-241 Donohue TJ, Kiley PJ and Kaplan S (1988) The puf operon of Rhodobacter sphaeroides. Photosynth Res 19:39--61 Draws G (1959) Beitrage zur Kennmis tier phototaktiscben Reaktiohen tier Cyanopbyceen. Arch Progstenkd 104:389-430 Draws G (1960a) Untersuchungen zur Substrnktur der Chrnmatophoren von Rhodospirillum rubrum und Rsp. molischianum. Arch Mikrobiol 36:99-108

Drews G (1960b) Untersuchungen zum Polyphospbatstoffwechsel und der Bildung metehromafischer Granula bei Mycobacterium phlei. Arch Mikrobiol 36:387--430 Drews G (1960c) Elektronenmikroskopische Untersuchungen an Mycobacterium phlei. Arch Mikrobiol 35:53-62 Drews G (1962) Physiologiscbe Untersuchungen an den Chromatophoren yon Rhodospirillum molischianum. Ber dtsch Bot Ges 75:338-344 Drews G (1964) Untersuchungen zur Photophosphorylierung bei R. molischianum und R. rubrum. Arch Mikrobiol 48:122-135 Drews G (1965) Untersuchungen zur Regulation der Bacteriochlorophyll Synthese bei R. rubrum. Arch Mikrnbiol 51:186-198 Drews G (1973) Fine structure and chemical composition of the cell envelopes. In: Cart NG and Wbitton BA (eds) The Biology of Blue-Green Algae, pp 99-116. Blackwen Science Publishers, Oxford Drews G (1978) Structure and development of the membrane system of photosynthetic bacteria, In: Sanada DR and Vernon LP (eds) Current Topics in Bioenergetics, Vol 8, pp 161-207. Academic Press, New York Drcws G (198 l) Rhodospirillum salexigens, spec. nov. an obligatory halophilic phototrophic bacterium. Arch Microbiol 130:325-327 Drcws G (1985) SU'ucturc and functional organization of lightharvesting complexes and photochemical reaction centers in membranes of phototrophic bacteria. Mictobiol Rev 49:59-70 Drews G and Dawes EA (exis) (1990) Molecular Biology of Membrane-Bound Complexes in Photo~ophic Bacteria. Plenum Press, New York Drews G and Giesbrecht P (1963) Zur Morphogenese der Bakterien Chromatophomn und zur Synthese des Bak~riocldorophyUs bei Rhodopseudomonas sphaeroides und Rhodospirillum rubrum. Zbl Bakt Parasitenkd Infek'fionskrenkh und Hyg I Orig 190:508-536 Drews G and Giesbrecht P (1965) Die Thylakoidstntkturen yon Rhodopseudomoru~s spec. Arch Mikrobiol 52:242-250 Drews G and Giesbrecht P (1966) Rhodopseudomonas viridis, nov. spec., ein neu isoliertes, obligat phototrophes Bakterium. Arch Mikrobio153:255-162 Drews G and Golecki JR (1982) Supramolocular organization and composition of membranes. In: Can" NG and Whitton BA (eds) The Biology of Cyanobacteria, pp 125-141. Blackwell Science Publishers, Oxford Drews G and Golccki JR (1995) Structure,molecular organization, and biosynthesis of membranes of purple bacteria. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 231-257. Kluwer Academic Publishers, Dordrecht. Drews G and Gollwitzer W (1965) Untersuchungen an tier Polysaccharidfraktion der Zellwande yon Anacys~ nidulans. Arch Mikrobio151:179-185 Drews G and Jager K (1963) Influence of light on the biosynthesis of bacteriochlorophyll by Rhodopseudomonas capsulata. Nature 199:1112-1113 Drews G and Meyer H (1964) Untersuchungen zum chemischen Aufbau der Zellwltnde von Anacystis nidulans und Chlorogloea fritschii. Arch Mikrobiol 48:259-267 Drews G and Niklowitz W (1956) Zentroplasma und granulate Einschltlsse von Phormidium uncinatum. Arch Mikrnbiol 24: 147162 Drews G and Niklowitz W (1957) Untersuchungen fiber die granul~en Einschl0sse tier Hormogonales. Arch Mikrobiol 25: 333351

347 Drews G and Oelz¢ J (1981) Organization and differentiation of membranes of photosynthetic bacteria. Adv Microb Physiol 22: 1-92 Drews G and Weckesser J (1982) Function, structure and composition of cell walls and external layers. In: Cart NG and Whitton BA (eds) The Biology of Cyanobacteria, pp 333-357. Biackwell Scientific Publishers, Oxford Drews G, Prauser H and Uhlmann D (1961) Massenvorkommen yon Synechococcus plancticus nov. spec. einer solit~iren planktischen Cyanophycee in einem Abwasserteich. Arch Mikxobiol 39: 10Ill5 Drews G, Lampe HH and Ladwig R (1969) Die Entwicklung des Photosyntheseapparates in Dunkelkulturen yon Rps. capsulata. Arch Mikrobioi 65:12-28 Drews G, Leutiger I and Ladwig R ( 1971) Production of protochlorophyll, protochlorophytin and bacteriochlorophyll by mutant A I a of Rps. capsulata. Arch Mikrobiol 76:349-363 Drews G, Dierstein R and Schumacher A (1976) Genetic transfer of the capacity to form bacteriochlorophyll-protein complexes in Rps. capsulata. FEBS Lett 68:132-136 Drews G, Wockesser J and Mayer LH (1978) Cell envelopes. In: Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 61-77. Plenum Press, New York Drews G, Ziser K, Schr0ck-Vietor V and Golecki JR (1988) Cellular responses of soybean to virulent and avirulent strains of Pseudomonas syringae, pv. glycinea. Europ J Cell Biol 46:369-375 Drews G, Hildig H, Mfintele W, Miiller M, Oelze J, Weckesser J and Welte W (eds) (1987) Workshop on Structure, Function and Formation of Membrane-bound Complexes in Phototrophic Bacteria. Abstracts, Freiburg. Duysens LNM (1951) Transfer of light energy within the pigment systems in photosynthetic cells. Nature (London) 168:548-550 Duysens LMN (1952) Transfer of excitation in photosynthesis. Thesis Utrecht Duysens LNM, Huiskamp WJ, Vos JJ and van der Hart JM (1956) Reversible changes in bacteriochlorophyll in purple bacteria upon illumination. Biochim Biophys Acta 19:188-190 Eimhjellen KE (1970) Thiocapsa pfennigii spec. nov. Arch Mikrobiol 73:194--194 Eimhjellen KE, Steensland LH and Tmetteberg LJ (1967) A Thiococcus nov. spec. gen., its pigments and internal membrane system. Arch Mikrobiol 59:82-92 Engelmann Th W (1888) 0her Bacteriopurpurin und seine physiologische Bedeutung. 11. 0her Blutfarbstoff als Mittel zur Untersuchung des Gaswechsels Chromophyll-haltiger Pflanzen im Licht und Dunkel. Archiv for die gesamte Physiologie des Menschen und der Tiere 42:183-188 Erasco JM and Kaplan S (1995) Oxygen-insensitive synthesis of the photosynthetic membranes of Rtmdobacter sphaeroides: A mutant histidine kinase. J Bacteriol 177:2695-2706 Esmarch E (1887) 0bet die Reinkultur eines Spirillum. Centralbl Bacteriol Parnsitenkd I: 225-230 Famintzin A (I 867) Die Wirkung des Lichtes auf Algen. Pringsheim Jh 6:1-54 Feick R and Drews G (1978) Isolation and characterization of lightharvesting bacteriochlorophyll complexes from Rps. capsulata. Biochim Biophys Acta 501: 499-5 ! 3 Feick R and Drews G (1979) Protein subunits of bacteriochlorophylls B802 and B855 of the light-harvesting complex II of Rps. capsulata. Z Naturfschg 34c: 196-199 Feher G and Okamura MY (1978) Chemical composition and properties of reaction centers. In: Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 349-386. Plenum Press, New York

Feiler U and Hauska G (1995) The reaction center from green sulfur bacteria. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 665-685. Kluwer Academic Publishers, Dordrecht Firsow NN and Drews G (1977) Differentiation of the intracytoplasmic membrane from Rhodopseudomonas palustris induced by variations of oxygen partial pressure or light intensity. Arch Microbiol 115:299-306 Foidl M, Golecki JR and Oelze J (1994) Bacteriochlorphyll c formation and chlorosome development in Chloroflexus aurantiacus. Photosynth Res 41:145-150 Fraker PJ and Kaplan S (1972) Isolation and characterization of a bacteriochlorophyll-containing protein from Rps. sphaeroides. J Biol Chem 247:2732-2737 Frank H, Lefort M and Martin HH (1962) Elektronenoptische und chemische Untersuchungen an Zeilw~lnden der Biaualge PluJrmidium uncinatum. Z Naturforsch 17b: 262-268 French CS (1938) The chromoproteins of photosynthetic purple bacteria. Science 88:60-62 Frenkel AW 0954) Light-induced phosphorylation by cell-free extracts of photosynthetic bacteria. J Am Chem Soc 76: 55685569 Frenkel AW (1956) Photophosphorylation of adenine nucleotides by cell-free preparations of purple bacteria. J Biol Chem 222: 823-834 Frenkel AW (1959) Light-induced reactions of bacterial chromatophores and their relation to photosynthesis. Annu Rev Plant Physiol 10:53-70 Frey-Wyssling A and Mtihlethaler K (1949) 0her den Feinbau der Chlorophyllk0mer. Vjschr Natufforsch Ges Z0rich 94:179-183 Garcia AF and Drews G (1980) Characterization of three membrane fractions isolated from cells of Rps. capsulata adapting from chemotrophic to phototrophic conditions. Arch Microbiol 127: 157-161 Garcia AE Vernon LP and Moilenhaner H (1966) Properties of Chromatium subchromatophore particles obtained by treatment with Triton X-100. Biochemistry 5:2399-2407 Garcia AF, Vernon LP, Ke B and Mollenhauer H (1968) Some structural and photochemical properties of Rhodopseudomonas spec. NHTC 133 subchromatophore particles obtained by treatment with Triton X-100. Biochemistry 7:326-332 Garcia AF, Reidl H and Drews G (1985) Efficiency of light conversion in photophosphorylation measured in chromatophores fused with liposomes and treated with inhibitors. Biochim Biophys Acta 808:180-185 Garcia AF, Venturoli G, Gad'on N, Fernandez-Velasco JG, Melandri BA and Drews G (1987) The adaptation of the electron transfer chain of Rps. capsulata to different light intensities. Biochim Biophys Acta 890:335-345 Gest H (1994) A microbiologist's odyssee: Bacterial viruses to photosynthetic bacteria. Photosynth Res 40:129-146 Gest H, San Pietro A and Vernon LP (eds) (1963) Bacterial Photosynthesis. The Antioch Press, Yellow Springs, OH Giesbrecht P and Drews G (1962) Elektronenmikroskopische Untersuchungen 0bet die Entwicidung der Chromatophoren yon Rsp. molischianum. Arch Mikrobiol 43:152-161 Giesbrecht P and Drews G (1966) Uber die Organisation und die makxomolekulare Architektur der Thylakoide 'lebender' Bakterien. Arch Mikrobiol 54:297-330 Ghosh R, Hauser H and Bachofen R (1988) Reversible dissociation of B873 light-harvesting complex from Rsp. rubrum G9. Biochemistry 27:10(M-1014

348 Gloe A, Pfennig N, Brockmann H and Trowitsch W (1975) A new bacteriochlorophyll from brown-colored chlorobiaceae. Arch Microbiol 102:103-109 Gober JW and Marques MV (1995) Regulation of cellular differentiation in Caulobacter crescentus. Microbiol Rev 59:31--47 Golecki JR and Drews G (1980) Cellular organization of the halophilic phototrophic bacterium strain WS 68. Eur J Cell Biol 22:654---660 Golecki JR and Drews G (1982) Supramolecular organization and composition of membranes. In: Carr NG and Whitton BA (eds) The Biology of the Cyanobacteria, pp 125-141. Blackwell Scientific Publications, Oxford Golecki JR and Oelze J (1975) Quantitative determination of cytoplasmic membrane invaginations in phototrophically growing Rsp. rubrum. J Gen Microbiol 88:253-258 Golecki JR and Oelze J (1987) Quantitative relationship between bacteriochlorophyll content, cytoplasmic membrane structure and chlorosome size in Chloroflexus auratiacus. Arch Microbiol 148:236-241 Golecki JR, Tadros MH, Ventura S and Oelze J (1989) Intracytoplasmic membrane vesiculation in light-harvesting mutants of Rba. sphaeroides and Rba. capsulatus. FEMS Microbiol Lett 65: 315-318 Golecki JR, Ventura S and Oelze J (1991) The architecture of unusual membrane tubes in the B800-850 light-harvesting bacteriochlorophyll-deficient mutant 19 of Rba. sphaeroides. FEMS Microbiol Lett 77:335-340 Gomelsky M and Kaplan S (1995) appA, a novel gene encoding a trans-acting factor involved in the regulation of photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1. J Bacteriol 172:4609-4618 Griffiths M, Sistrom WR, Cohen-Bazire G and Stanier RY (1955) Function of carotenoids in photosynthesis. Nature 176: 12111214 Guner S, Willie A, Millet F, Caffrey MS, Cusanovich MA, Robertson DE and Knaff DB (1993) The interaction between cytochrome c2 and the cytochrome bCl-complex in the photosynthetic purple bacteriaRba, capsulatus and Rps. virldis. Biochemistry 32: 47934800 Harashima K, Shiba T and Murata N (1989) Aerobic Photosynthetic Bacteria. Springer Verlag, Berlin, Heidelberg Harder H (1918) Uber die Bewegung der Nostocaceen. Ztschr Bot I0:177-244 Harder H (1920) Ober die Bewegung frei beweglicher pflanzlicher Organismen. Ztschr Bot 12:353-462 Harold FM (1995) From morphogenes to morphogenesis. Microbiology 141:2765-2778 Holt SC and Marr AG (1965a) Location of chlorophyll in Rsp. rubrum. J Baeteriol 89:1402-1412 Holt SC and Marr AG (1965b) Effect of light intensity on the formation of intracytoplasmic membrane in Rsp. rubrum. J Bacteriol 89:1421-1429 Holzwarth AR and Schaffner K (1994) On the structure of bacteriochlorophyll molecular aggregates in the chlorosomes of green bacteria. A molecular modelling study. Photosynth Res 41: 225233 Homberger U, Liebetanz R, Tichy H-V and Drews G (1990) Cloning and sequencing of the hemA gene ofRhodobacter capsulatus, and isolation of a 6-aminolevulinate-dependent mutant strain. Mol Gen Genet 221:371-378 Hornberger U, Wieseler B And Drews G (1991) Oxygen tension regulated expression of the hemA gene of Rba. capsulatus. Arch Microbiol 156:129-134

Hiidig H, Stark G and Drews G (1987) The regulation of cytochrom c oxidase of Rhodobacter capsulatus by light and oxygen. Arch Microbiol 149:12-18 Hunter CN (1988) Transposon Tn5 mutagenesis of genes encoding reaction centre and light-harvesting I polypeptides of Rba. sphaeroides. J Gen Microbiol 134:1481-1489 Hunter CN (1995) Genetic manipulation of the antenna complexes of purple bacteria. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 473-501. Kluwer Academic Publishers, Dordrecht Hunter CN, Holmes NG, Jones OTG and Niederman RA (1979) Membranes of Rps. sphaeroides. VII Photochemical properties of a fraction enriched in newly synthesized bacteriochlorophyll -protein complexes. Biochim Biophys Acta 548:253-266 Hunter CN, Pennoyer JD, Sturgis JN, Farelly D and Niederman RA (1988) Oligomerization states and associations of lightharvesting pigment-protein complexes of Rba. sphaeroides as analyzed by lithium dodecyl sulfate polyacrylamide gel eleetrophoresis. Biochemistry 27:3459-3467 Hurlbert RE, Golecki JR and Drews G (1974) Isolation and characterization of Chromatium vinosum membranes. Arch Microbiol 101:169-186 Huzisige H and Ke B (1993) Dynamics of the history of photosynt research. Photosynth Res 38:185-209 Inoue K, Kouadio J-LK, Mosley CS and Bauer CE (1995) Isolation and in vitro phosphorylation of sensory transduction components controlling anaerobic induction of light harvesting and reaction center gene expression in Rhodobacter capsulatus. Biochemistry 34:391-396 Jay F, Lambilotte M and MUhlethaler K (1983) Localization of RtuMopseudomonas viridis reaction centre and light-harvesting proteins using ferritin-antibody labelling. EurJ Cell Biol 30:1-8 Jensen A, Aasmundrud O and Eimhjellen KE (1964) Chlorophylls of photosynthetic bacteria. Biochim Biophys Acta 88:466--479 Jttrgens U and Weckesser J (1986) Polysaccharide covalently linked to the peptidoglycan on Synechocystis spec. strain PCC 6714. J Bacteriol 168:568-573 JOrgens UJ, Drews G and Weckesser J (1983) Primary structure of the peptidoglycan from the unicellular cyanobacterium Synechocystis sp- strain PCC 6714. J Bacteriol 154:471--478 Kamen MD (1980) A capful of luck, a pinch of sagacity. Annu Rev Biochem 55:1-34 Kaplan S (1978) Control and kinetics of photosynthetic membrane development. In: Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 809-839. Plenum Press, New York Kaplan NO and Robinson A (eds) (1982) From Cyclotrons to Cytochromes. Essays in Molecular Biology and Chemistry. Academic Press, New York Karrasch S, Bullough PA and Ghosh R (1995) The 8.5 ~ projection map of the light-harvesting complex I from Rsp. rubrum reveals a ring composed 16 subunits. EMBO J 14:631--638 Kaufmann N, Hiidig H and Drews G (1984) Transposon Tn5 mutagenesis of genes for the photosynthetic apparatus in Rps. capsulata. Mol Gen Genet 198:153-158 Kiley PJ, Vargat A and Kaplan S (1988) Physiological and structural analysis of light-harvesting mutants of Rba. sphaeroides. J Bacteriol 170:1103-1115 King MT and Drews G (1975) The respiratory electron transport system of heterotrophically grown Rps. palustris. Arch Microbiol 102:219-231 King MT and Drews G (1976) Isolation and partial characterization of the cytochrome oxidase from Rps. palustris. Eur J Biocbem 68:5-12

349 Klug G (1995) Post-transcriptional control of photosynthesis gene expression, in: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 1235-1244. Kluwer Academic Publishers, Dordrecht Klug G and Cohen SN (1988) Pleiotropic effects of localized Rba. capsulatus pufoperon deletions on production of light-absorbing pigment-protein complexes. J Bacteriol 170:5814-5821 Klug G, Kanfmann N and Drews G (1985) Gene expression of pigment-binding proteins of the bacterial photosynthetic apparatus: Transcription and assembly in the membrane ofRps, capsulata. Proc Natl Acad Sci USA 82:6485-6489 Klug G, Liebetanz R and Drews G (1986) The influence of bacteriochlorophyll biosynthesis on formation of pigment-binding proteins and assembly of pigment-protein complexes in Rps. capsulata. Arch Microbiol 146:284-291 Kiug G, Adams CW, Belasco J, Doerge B and Cohen'SN (1987) Biological consequences of segmental alterations in mRNA stability: Effects of deletion of the intercistronic hairpin loop region of the Rba. capsulatus pufoperon. EMBO J 6:3515-3520 Kok B (1961) Partial purification and determination of oxidationreduction potential of the photosynthetic chlorophyll complex absorbing at 700 m#. Biochim Biophys Acta 48:527-532 Komiya H, Yeates TO, Rees DC, Allen JP and Feher G (1988) Structure of the reaction center from Rba. sphaeroides. Proc. Natl Acad Sci USA 85:9012-9016 Lampe HH and Drews G (1972) Die Differenzierung des Membransystems yon Rps. capsulata hinsichtlich seiner photosynthetisthen and respiratorischen Funktionen. Arch Mikrobiol 84:1-19 Lang HP and Hunter CN (1994) The relationship between biosynthesis and the assembly of the light-harvesting LH2 complex in Rba. sphaeroides. Biochem J 298:197-205 Lascelles J (1959) Adaptation to form bactedochlorophyU in Rps. sphaeroides. Biochem J 72:508-518 Lascelles J (1966) The accumulation of bacteriochlorophyll precursors by mutant and wild-type strains of Rps. sphaeroides. Biochem J 100:175-183 Lascelles J (1978) Regulation of pyrrole synthesis. In: Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 795-808. Plenum Press, New York Lascelles J and Altshuler T (1967) Mutant strains of Rps. sphaeroides lacking 6-amiuolevulinate synthase. J Bacteriol 98:721-727 Lascelles J and Wertlieb D (1971) Mutant strains ofRps, sphaeroides which form photosynthetic pigments aerobically in the dark. Biochim Biophys Acta 226:328-340 Lee JK and Kaplan S (1995) Transcriptional regulation ofpuc operon expression in Rhodobacter sphaeroides. J Bioi Chem 270: 20453-20458 Leyon H and yon Wettstein D (1954) Der Chromatophoren Feinbau hei den Phaeophyceen. Z Naturfsch 9b: 471-475 Liebetanz R, Horoberger U and Drews G (1991) Organization of the genes coding for the reaction centre L and M subunits and B870 antenna polypeptides and from the aerobic photosynthetic bacterium Erythrobacter spec. OCH114. Mol Microbiol 5: 14591468 Loach PA and Parkes-Loach PS (1995) Structure-function relationship in core light-harvesting complexes as determined by characterization of the structural subunit and by reconstitution experiments. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 437-471. Kluwer Academic Publishers, Dordrecht Lommen MAJ and Takemoto J (1978) Uitrastructure of carotenoid mutant strain R-26 of Rps. sphaeroides. Arch Microbiol 118: 305-308

Mantele W, Stock K, Becker A, Wacker T, Welte W, Gad'on N and Drews G (1988) Spectroscopic studies of crystallized pigmentprotein complexes ofRps, palustris. In: Breton J and Vermtglio A (eds) Structure of Bacterial Reaction Centers: X-Ray Crystallography and Optical Sectroscopy with Polarized Light. Nato Adv Study Set A, Vol 149, pp 33-39. Plenum Press, New York Marts BL (1974) Genetic recombination in RluMopseudomonas capsulata. Proc Natl Acad Sci USA 71:971-973 Marrs BL (1981) Mobilization of the genes for photosynthesis from Rps. capsulata by a promiscuous plasmid. J Bacteriol 146: 10031012 Marts BL and Gest H (1973) Regulation of bacteriochlorophyll synthesis by oxygen in respiratory mutants ofRps, capsulata. J Bacterioi 114:1052-1057 McDermott G, Prince SM, Freer AA, Hasthomthwaite-Lawless AM, Papiz MZ, Cogdell PU and lsaacs NW (1995) Crystal structure of an integral membrane light-harvesting complex from photosynthetic bacteria. Nature (London) 374:517-521 Meadows KA, Iida K, Tsuda K, Recchina PA, Heller BA, Antonio B, Nango M and Loach PA (1995) Enzymatic and chemical cleavage of the core light-harvesting polypeptides of photosynthetic bacteria: Determination of the minimal polypeptide size and structure required for subunit and light-harvesting complex formation. Biochemistry 34:1559-1574 Meckenstock RU, Krosche K, Brunisholz RA and Zuher H (1992) The light-harvesting core complex and the B820 subunit from Rps. marina. FEBS Lett 31 i: 128-134 Meryandini A and Drews G (1996) Import and assembly of the c~ and fl-polypeptides of the light-harvesting complex I (B870) in the membrane system of Rhodobacter capsulatus investigated in an in vitro translation system. Photosynth Res, 47:21-31 Michel H, Weyer KA, Gruenherg H and Lottspeich F (1985) The heavy subunit of the photosynthetic reaction centre from Rhodopseudomonas viridis: Isolation of the gene, nucleotide and amino acid sequence. EMBO J 4:1667-1672 Michel H, Weyer KA, Gruenherg H, Dunger I, Oesterhelt D and Lottspeieh F. (1986) The light and medium subunits of the photosynthetic reaction centre from Rhodopseudomonas viridis: Isolation of the genes, nucleotide and amino acid sequence. EMBO J 5:1149-1158 Mitchell P (1966) Chemiosmotic coupling in oxidative and photosynthetic phosphorylation. Biol Rev 41:445-502 Molisch H (I 907) Die Purpurbakterien nach neuen Untersuchungen. Gustav Fischer Vlg Jena Nagashima KVP, Matsuura K, Ohyama S and Shimada K (1994) Primary structure and transcription of genes encoding B870 and photosynthetic reaction centre apoprotein from Rubruvivax gelatinosus. J Biol Chem 269:2477-2484 Newton JW and Newton GA (1956) Composition of the photoactive subcellular particles from Chromatium. Arch Biochem Biophys 71: 250-265 Niederman, RA, Mallon DE and Parks LCC (1979) Membranes of Rps. sphaeroides VI: Isolation of a fraction enriched in newly synthesized bacteriochiorophyll a-protein complexes. Biochim Biophys Acta 555:210-220 Nienburg W (1916) Die Perzeption des Lichtreizes bei den Oscillatorien und ihre Reaktion anf Intensitiitsschwankungen. Ztschr Bot 8:161-193 Nieth KF and Drews G (1974) The protein patterns of intracytoplasmic membranes and reaction center particles isolated from Rps. capsulata. Arch Microbiol 96:161-174 Nieth KF and Drews G (1975) Formation of reaction centers and light-harvesting bacteriochlorophyU-protein complexes in Rps. capsulata. Arch Microbiol 104:77-82

350 Niklowitz W and Drews G (1955) Zur elektronenmikroskopischen Darstellung der Feinstruktur yon Rhodospirillum rubrum. Arch Mikrobiol 23:123-129 Niklowitz W and Drews G (1956) Untersuchungen zur Substruktur von PtuJrmidium uncinatura. Arch Mikrobiol 24:134-146 Niklowitz W and Drews G (1957) Vergleichende elektronenmikroskopische Untersuchungen zur Substruktur einiger Hormogonales. Arch Mikrobiol 27:150-165 Nozaki M, Tagawa K and Amon D! (1963) Certain aspects of cyclic and noncyclic photophosphorylation in Rtu~dospirillum rubrum. In: Gest H, San Pietro A and Vernon LP (eds) Bacterial Photosynthesis. The Antioch Press, Yellow Springs, OH Nultsch W (1975) Phototaxis and photokinesis. In: Carlile MJ (ed) Primitive Sensory and Communication Systems, pp 29-90. Academic Press, London Nultsch W (1985) Lichtorientierte Bewegungen hei Cyanobakterien. Naturwissenschaften 72:527-533 Nultsch W, Schuchart and HOhi M (1979) Investigations on the phototactic orientation of Anabaena variabilis. Arch Microbiol 122:85-91 Oberl6 B, Tichy HV, Homberger U and Drews G (1990) Regulation of formation of photosynthetic light-harvesting complexes in Rba. capsulatus. In: Drews G and Dawes EA (eds) Molecular Biology of Membrane-Bound Complexes in Phototrophic Bacteria, pp 77-84. Plenum Press, New York Oelze J (1992) Light and oxygen regulation of the synthesis of bacteriochlorophyil a and c in Chloroflexus aurantiacus. J Bacteriol 174:5021-5026 Oelze J and Drews G (1969) Die Morphogenese des Photosyntheseapparates yon Rsp. rubrura, II. Die Kinetik der Thylakoidsynthese nach Markierung der Membranen mit [2-14C] Azetat. Biochim Biophys Acta 173:448--455 Oelze J and Drews G (1970) Der Einfluss der Lichtintensitiit und der Sauerstoffspannung auf die Differenzierung der Membranen von Rsp. rubrum. Biochim Biophys Acta 203:189-198 Oelze J and Pablke W (1976) The early formation of the photosynthetic apparatus in RluJdospirillum rubrum. Arch Microbiol 108: 281-285 Oelze J, Biedermann M and Drews G (1969a) Die Morphogenese des Photosyntheseapparates yon Rsp. rubrum I. Die lsolierung and Charakterisierung yon zwei Membransystemen. Biochim Biophys Acta 173:436--447 Oelze J, Biedermann M, Freund-M61hert E and Drews G (1969b) Bacteriochlorophyllgehalt und Proteinmuster der Thylakoide yon Rsp. rubrum wllluend der Morphogenese des Photosyntheseapparates. Arch Mikrobiol 66:154-165 Ohad I and Drews G (1982) Biogenesis of the photosynthetic apparatus in prokaryotes and eukaryotes. In: Govindjee (ed) Photosynthesis: Development, Carbon Metabolism and Plant Productivity, Vol I1, pp 89-140. Academic Press, New York Oling F, Boekema F,J, de Zarate I O, Visschers R, van Grondelle R, Keegstra W, Brisson A and Picorel R (1996) Two-dimensional crystals of LH2 light-harvesting complexes from Ectothiorhodospira sp. and Rhodobacter capsulatus investigated by electron microscopy. Biochim Biophys Acta 1273:44-50 Pardee AB, Schachman HK and Stanier RY (1952) Chromatophores of RluJdospirillum rubrum. Nature 169:282-283 Pieper A (1913) Die Diaphototaxis der Oscillatorien. Ber dtsch Bot Ges 31 : 594-599 Pfennig N (1993) Refections of a microbiologist, or how to learn from the microbes. Annu Rev Microbiol 47:1-29 Porra RJ, Sch~er W, Gad'on N, Katheder 1, Drews G and Scheer H (1996) Origin of the two carbonyl oxygens of bacteriochlorophyll a: Demonstration of two different pathways for the formation of

ring E in Rhodobacter sphaeroides and Roseobacter denitrificans and of a common hydratase mechanism for 3-acetyl group formation. Europ J Biochem, in press Reed DW (1969) Isolation and composition of a photosynthetic reaction center complex from Rhodopseudomonas sphaeroides. J Biol Chem 244:4936-4941 Reidl H, Golecki JR and Drews G (1983) Energetic aspects of photophosphorylation capacity and reaction center content of Rps. capsulata grown in a turbidostat under different irradiances. Biochim Biophys Acta 725:455--463 Reidl H, Golecki JR and Drews G (1985) Composition and activity of the photosynthetic system ofRps, capsulata. The physiological role of the B800--850 light-harvesting complex. Biochim Biophys Acta 808:328-333 Richter P and Drews G (1991) Incorporation of light-harvesting polypeptides into the intracytoplasmic membrane of Rba. capsulatus. J Bacteriol. 173:5336-5345 Richter P, Cortez N and Drews G (1991) Possible role of the highly conserved amino acids Trp-8 and Pro-13 in the N-terminal segment of the pigment-binding polypeptide LH I s of Rb. capsulatus. FEBS Lett 285:80-84 Richter P, Brand M and Drews G (1992) Characterization of LH I - and LH I+ Rba. capsulatus pufA mutants. J Bacteriol 174: 3030-3041 Ris H and Singh RN (1961) Electron microscope studies on bluegreen algae. J Biophys Biochem Cytol 9:63-80 Sabaty M and Kaplan S (1996) mgpS, a complex regulatory locus involved in the transcriptional control of the puc and pufoperons in Rhodobacter sphaeroides 2.4.1. J Bacteriol 178:35--45 Schachman HK, Pardee AB and Startler RY (1952) Studies on the macromolecular organization of microbial cells. Arch Biochem Biophys 38:245-260 Schmid G (1921) 0ber Organisation und Schleimbildung bei Oscillamria jenensis. Pringsh Jb 60:572--627 Schmid G (1923) Das Reizverhalten kilnstlicher TeilstUcke, die Kontraktilitat und das osmotische Verhalten der Oscillatoriajenensis. Pringsh Jb 62:328--419 Schmitz R (1967) Uher die Zusammensetzung der pigmenthaltigen Strukturen aus Prokaryonten. Arch Mikrobiol 56:225-237 Schtin G (1971) Der Einflul~ tier Kulturhedingungen auf den Nicotinamid-Adenin dinucleotid (phosphat)-Gehalt in Zellen von Rsp. rubrum. Arch Microbiol 79:147-163 Schumacher A and Drews G (1978) The formation of bacteriochlorophyll-protein complexes of the photosynthetic apparatus of Rhodopseudomonas capsulata during early stages of development. Biochim Biophys Acta 501:183-194 Schumacher A and Drews G (1979) Effect of light intensity on membrane differentiation in Rps. capsulata. Biochim Biophys Acta 547:417--428 Shiozawa JA, Cuendet PA, Drews G and Zuber H (1980) Isolation and characterization of the polypeptide components from lightharvesting pigment-protein complex B800-850 of Rba. capsulatus. Eur J Biochem 111: 455--460 Shiozawa JA, Weite W, Hodapp N and Drews G (1982) Studies on the size and composition of the isolated light-harvesting B800850 pigment-protein complex of Rba. capsulatus. Arch Biochem Biophys 213:473-485 Sistrom WR (1977) Transfer of chromosomal genes mediated by plasmid R 68.45 in Rba. sphaeroides. J Bacteriol 131:526-532 Sistrom WR and Clayton RK (1964) Studies on a mutant of Rps. sphaeroides unable to grow photosynthetically. Biochim Biophys Acta 88:61-73

351 Socket RE, Donohue TJ, Varga AR and Kaplan S (1989) Control of photosynthetic membrane assembly in Rba. sphaeroides mediated by puhA and flanking sequences. J Bacteriol 171:436 4"!.6 Staehelin LA, Golecki JR, Fuller RC and Drews G (1978) Visualization of the supramolecular architecture of chlorosomes in freeze-fractured cells of Chloroflexus auratiacus. Arch Microbiol 119:269-277 Staehelin LA, Golecki JR and Drews G (1980) Supramolecular organization of chlorosomes and their membrane attachment sites in Chlorobium limicola. Biochim Biophys Acta 589:30--45 Stahl E (1880) Uber den Einflufl von Richtung and Stiirke der Beleuchtung auf einige Bewegungserscheinungen im Pflanzenreich. Bot Ztg 38:409--412 Stanier RY (1980) The journey, not the arrival matters. Annu Rev Microbiol 34:1-48 Steinmann E (1952) An electron microscope study of the lamellar structure of chloroplasts. Exp Cell Res 3:367-372 Steinmann E and Sj6strand FS (1955) The ultrastructure of chloroplasts. Exp Cell Res 8:15-23 Stiehle H, Cortez N, Klug G and Drews G (1990) A negatively charged N-terminus in the c~-polypeptide inhibited formation of the light-harvesting complex 1 in Rba. capsulatus. J Bacteriol 172:7131-7137 Straley SC, Parson WW, Mauzerall DC and Clayton RK (1973) Pigment content and molar extinction coefficients of photochemical reaction centers from Rlu~dopseudomonas sphaeroides. Biochim Biophys Acta 305:597-609 Tadros MH and Drews G (1990) Pigment-proteins of antenna complexes from purple non-sulfur bacteria. In: Drews G and Dawes EA (eds) Molecular Biology of Membrane-Bound Complexes in Phototrophic Bacteria, pp 181-192. Plenum Press, New York Tadros MH, Suter F, Drews G and Zuber H (1983) The complete amino acid sequence of the large bacteriochlorophyll-binding polypeptide from light-harvesting complex II of Rba. capsulatus. EurJ Biochem 129:533-536 Tadros LMH, Frank R and Drews G (1985) The complete amino acid sequence of the small bacteriochlorophyll-binding polypeptide B800-850 from light-harvesting complex B800-850 of Rba. capsulatus. FEBS Lett 183:91-94 Tadros MH, Frank R, DOrge B, Gad'on N, Takemoto JY and Drews G (1987) Orientation of the B800-850, B870 and reaction center polypeptides on the cytoplasmic and periplasmic surfaces of Rba. capsulatus. Biochemistry 26:7680-7687 Tauschel HD and Drews G (1967) Thylakoidmorphogenese bei Rhodopseudomonas palustris. Arch Mikrobiol 59:381-404 Thornher JP, Trosper TL and Strouse CE (1978) Bacteriochlorophyll in vivo: Relationship of spectral forms to specific membrane components. In: Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 133-160. Plenum Press, New York Tichy HV, Obefl6 B, Stiehle H, Schiltz E and Drews G (1989) Genes downstream from pucB and pucA ate essential for formation of the B800-850 complex of Rhodobacter capsulatus. J Bacteriol 171:4914--4922 Tichy HV, Albien KU, Gad'on N and Drews G (1991) Analysis of the RluJdobacter capsulatus puc operon: The pucC gene plays a central role in the regulation of LH II(B800-850) complex expression. EMBO J 10:2949-2955 Troschei D and Milller M (1990) Development of a cell-free system to study the membrane assembly of photosynthetic proteins of Rba. capsulatus. J Cell Biol 1 ! 1: 87-94 van Niel CB (1932) On the morphology and physiology of the purple and green sulphur bacteria. Arch Mikrobiol 3:1-112

van Niel CB (1944) The culture, general physiology, morphology and classification of the non-sulfur purple and brown bacteria. Bacteriol Rev 8:1-118 van Niel CB (1967) The education of a microbiologist; some reflections. Annu Rev Microbiol 21:1-30 Verm6glio A, Joliot P and Joliot A (1995) Organization of electron transfer components and supercomplexes. In: Blankenship RE, Madigan MT and Bauer CE (eds) Anoxygenic Photosynthetic Bacteria, pp 279-295. Kluwer Academic Publishers, Dordrecht von Heijne G (1994) Membrane proteins: from sequence to structure. Annu Rev Biophys Biomol Struct 23:167-192 Vredenberg WJ and Duysens LNM (1963) Transfer of energy from bacteriochlorophyli to a reaction center during bacteriochlorophyll photosynthesis. Nature 197:355-357 Wacker T, Gad'on N, Becker A, Miintele W, Kreutz W, Drews G and WeRe W (1986) Crystallization and spectroscopic investigation with polarized light of the reaction center-B875 light-harvesting complex of Rlu~dopseudomonas palustris. FEB S Lett 197: 267273 Wall JD, Weaver P and Gest H (1975) Gene transfer agents, bacteriophages and bacteriocines. Arch Microbiol 105:217-224 Weaver P (1971 ) Temperature-sensitive mutations of the photosynthetic apparatus of Rsp. rubrum. Proc Natl Acad Sci USA 68: 136-138 Weckesser J, Drews G and Fromme I (1972) Chemical analysis of and degradation studies on the cell wall lipopolysaccharide of Rps. capsulata. J Bacteriol 109:1106-1113 Weckesser J, Drews G, Mayer H and Fromme I (1974a) Lipopolysaccharid aus Rhodospirillaceae, Zusammensetzung und taxonomische Relevanz. Zbl Bakt Hyg I Abt Orig A 228:193-198 Weckesser J, Drews G, Roppel J, Mayer H and Fromme I (1974b) The lipopolysaccharide of Rhodopseudomonas viridis. Arch Microbiol 101: 233-245 Weckesser J, Drews G and Mayer H (1979) Lipopolysaccharides of photosynthetic prokaryotes. Annu Rev Microbiol 33:215-239 Weise G, Drews G, Jann B and Jann K (1970) Identification and analysis of a lipopolysaccharide in cell walls of the blue-green alga Anacystis nidulans. Arch Mikrobiol 71:89-98 Wellington CL and Beatty JT (1991) Overlapping mRNA transcripts of photosynthetic gene operons in Rba. capsulatus. J Bacteriol 173:1432-1443 WeRe W, Wacker T, Leis M, Kreutz W, Shiozawa I, Gad'on N and Drews G (1985) Crystallization of the photosynthetic lightharvesting pigment-protein complex B800-850 ofRba, capsulams. FEBS Lett 182:260-264 Wiessner C, Dunger I and Michel (1990) Structure and transcription of the genes encoding the B 1012 light-harvesting complex and ot-subunits and the photosynthetic reaction center L, M and cytochrome c subunits from Rps. viridis. J Bacteriol 172: 28772887 Witt HT, Miiller A and Rumberg B (1961a) Experimental evidence for the mechanism of photosynthesis. Nature (London) 191: 194195 Witt HT, MUller A and Rnmherg B (1961b) Oxidized cytochrome and chlorophyll in photosynthesis. Nature 192:967-969 Wolken JJ and Palade GE (1952) Fine structure of chloroplasts in two flagellates. Nature (London) 170:114 Wolken JJ and Palade GE (1953) An electron microscope study of two flagellates. Ann New York Acad Sci 56:873 Yen H-C and Marrs B (1976) Map of genes for carotenoid and bacteriochlorophyll biosynthesis in Rps. capsulata. J Bacteriol 126:~619-629

352 Yildiz TH, Gest H and Bauer CE (1991) Attenuated effect of oxygen on photopigment synthesis in Rhodospirillum centenum. J Bacteriol 173:5502-5506 Yildiz FH, Gest H and Bauer CE (1992) Conservation of the photosynthesis gene cluster in Rsp. centenum. Mol Microbiol 6: 26832691 Young DA, Bauer CE, Williams JC and Marrs BL (1989) Genetic evidence for superoperonal organization of genes for photosynthetic pigments and pigment-binding proteins in Rba. capsulatus. Moi Gen Genet 218:1-12 Youvan DC, Bylina El, AIberti AM, Begusch H, and Hearst JE (1984) Nucleotide and deduced polypeptide sequences of the photosynthetic reaction center, B870 antenna and flanking sequences from Rps. capsulata. Cell 37:949-957 Yurkov V, Stackebrandt E, Holmes A, Faerst JA, Hugenholtz E Golecki J, Gad'on N, Gorlenko VM, Kompantseva El and Drews G (1994) Phylogenetic positions of novel aerobic, bacteriochlorophyll a- containing bacteria and description ofRoseococcus thio-

sulfatophilus gen. nov., sp. nov., Erythromicrobium ramosum gen. nov., sp. nov., and Erythrobacter litoralis sp. nov. Int J Syst Bacteriol 44:427-437 Zilinsky JW, Sojka GA and Gest H (1971) Energy charge regulation in photosynthetic bacteria. Biochem Biophys Res Commun 42: 955-961 Zsebo KM and Hearst JE (1984) Genetic-physical mapping of a photosynthetic gene cluster from Rps. capsulata. Cell 37: 937947 Zuber H (1990) Considerations on the structural principles of the antenna complexes of phototrophic bacteria. In: Drews G and Dawes EA (eds) Molecular Complexes in Phototrophic Bacteria, pp 161-180. Plenum Press, New York Zurdo J, Centeno MA, Odriozola JA, FernAndez-Cabrera C a m d Ramirez JM (1995) The structural role of the carotenoid in the bacterial light-harvesting protein 2 (LH2) of Rhodobacter capsulatus. A Fourier transform Raman spectroscopy and circular dichroism study. Photosynth Res. 46:363-369