J. Basic Microbiol. 32 (1992) 3, 185-192
(Scientific-Industrial Union “Bacteriophage”, Tbilisi, Georgia - 380 060. ‘Institute of the Physics of the Earth, Academy of Sciences, Moscow - 123 810, Russia and *European Molecular Biological Laboratory, W-6900 Heidelberg, Germany)
Magnetotactic bacteria from freshwater lakes in Georgia ELWINAA. MATITASHVILI, DIANAA. MATOJAN,TATJANAS. GENDLER’,TEYMURAS V. KURZCHALIA’ a n d REVAZS. ADAMIA (Received 22 Nouernber 1991/Accepted 6 December 1991)
Several species of magnetotactic bacteria were discovered in the lakes and ponds of Georgia. Electron microscopic analysis of the bacteria showed a great variety of microbial forms as well as magnetosome arrangements. Pyramidal, cubical or hexagonal magnetic grains could be seen in different species of bacteria. The linear organization of magnetic particles was prevailing, although gathered magnetosomes were also seen. Magnetometric measurement of magnetic particles obtained from coccoid bacteria was performed. Remnent acquisition curves, as well as thermomagnetic curves of investigated material showed that the magnetosomes under study contained pure single-domain magnetite. Magnetotactic bacteria, first discovered mo r e than 15 years ago by BLAKEMORE (1975), still remain one of the most intriguing organisms of the microbial world. In the years since their discovery several groups o f scientists have studied some of the biochemical a nd morphophysiological properties of these bacteria. These studies have determined several
of the basic characteristics of these microorganisms (BALKWILL et at. 1980, BLAKEMORE 1982, T o w a n d MOENCH1981). However, a number of the most interesting and important questions still remain unanswered: What is the transportation mechanism of the iron ions f r o m the surrounding medium into the bacterial cells? How are the number and dimensions of the ferromagnetic domains determined? What determines the location of the locomotion system such that nearly all the cells in a given population move in the same direction? The most important factor-hindering progress in the study of magnetotactic bacteria is the fact that, until now, only one species - Aquaspirilium rnagnetotacticum - could be cloned to obtain a pure culture (BLAKEMORE et al. 1979). However, the complicated cultivation conditions f o r this spirillum are unsuitable f o r t h e production of large quantities of bacteria or bacterial magnetite for industrial purposes. These considerations spurred us t o search for new species of magnetotactic bacteria in lakes and freshwater reservoirs of Georgia.
Materials and methods The magnetotactic bacteria used were found in ponds and lakes in Georgia, with 8 out of 49 samples proving positive. The bacteria were located on the northern shores, in regions of muddy water with surface growth of reeds and algae. The mud to water ratio of the samples was 1 : 3. The samples were incubated in loosely capped bottles at room temperature and under weak illumination for one to several months to allow the magnetotactic bacteria to accumulate. Magnetotactic bacteria were collected by means of a steady magnet, using the equipment described by MATSUNACA and KAMrYA (1987). The bacteria were detected using a NICONTMD-2 microscope. Morphological studies of both bacteria and isolated magnetosomes were carried out using a JEM 1200 EX electron microscope.
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Isolation was effected by spinning the magnetotactic cell suspension in a centrifuge and resuspending the pellet in 5 M NaOH. After 18 hours magnetic particles were spun down and washed several times in distilled water. isolated magnetic grains were mixed with MgO powder (nonmagnetic matrix) in 1 : 50 ratio and packed into a cylindrical quarts cell(s). which has an extremely low magnetic noise level (saturation remanencr magnetization approximately 4.1 x Am2/kg). Measurements of isothermal remnent magnetization (J,) acquired in fields up to 2.5 Tesla were carried out with the spinner magnetometer with sensitivity 1.6 x Am’. Saturation magnetization (J,) as a function of temperature was measured with continuous thermal demagnetization method. To avoid the effect of contamination, all the magnetic measurements were done for pure MgO powder as well.
Results and discussion Magnetotactic bacteria usually inhabit reservoirs rich in organic substances; small eutrophic lakes, ponds and muddy, swampy areas are the best environments (BLAKEMORE 1982). In the northern hemisphere most of the microorganisms in the population gather on the northern shores of reservoirs.
Fig. 1 Magnetotactic bacterium with pyramidal magnetosomes occurring in Eastern Georgia. Bar represents 700 nm
Magnetotactic bacteria from freshwater lakes
187
Fig. 2 Coccoid magnetotactic bacteria chosen for detailed study of magnetosomes structure and organization. Bar represents 500 nm
188
E. A. MATITASHVILI et al.
These factors influenced the choice of location where magnetotactic bacteria were sought. The lakes and ponds which were searched abound in organic substances, both naturally occurring and as the result of human activity. As the magnetotactic bacteria under study are microaerophiles (BLAKEMORE et al. 1985), or more rarely, obligate anaerobes (BAZYLINSKI et al. 1988), the samples were collected at a depth of 10 - 60 cm, all due precautions being observed. Experimental work led to discovery of several species of bacteria which respond to the earth magnetic field, as well as to the field generated by a small steady magnet. Morphological studies showed great variety among the magnetotactic bacteria. Bacteria isolated from one of the lakes in eastern part of Georgia (Fig. l), are rod shaped and have one chain of magnetic grains. These particles are pyramidal in shape, with a base of 50 nm x 50 nm, and a height of 150 nm. BLAKEMORE (1982) noted the occurrence of such bacteria in the southern hemisphere, in New Zealand. Samples taken from a natural pond in the Pioneer Park in Batumi proved extremely rich in magnetotactic bacteria. Surprisingly, water samples of this reservoir contained several different species of magnetotactic microorganisms. Prevailing part of the magnetotactic microphlore consisted of coccoid bacteria (Fig. 2a). which possess well-developed, polarly located flagellar motor system (Fig. 2b). These microorganisms contain two chains of magnetic particles of almost cubical form, with dimensions 80 nm x 80 nm x 100 nm. Considerably less amounts of rod-shaped magnetotactic bacteria were discovered in the same pond (Fig. 3). These microorganisms also contained magnetic particles arranged as a chain. Such an arrangement makes biological sense, as it significantly increases the total magnetic moment of the bacterial cells (BLAKEMORE 1982). However, in the same pond the magnetotactic bacteria were discovered in which the magnetic particles were not arranged as a chain but gathered in groups in distinct parts of the cells (Fig. 4). It seems, that the
Fig. 3 Rod-shaped bacteria with linear arrangement of magnetosomes. Bar represents 500 nm
Magnetotactic bacteria from freshwater lakes
189
Fig. 4 Non-linear organization of magnetosomes in magnetotactic bacterial cells. Bar represents 500 nm
arrangement of magnetic particles is determined by the bacterial cell itself, but does not depend on the applied magnetic field. The arrangement of magnetic particles in flagellar-like structures was striking (Fig. 5). To our mind, such location of magnetic particles has not been detected earlier. Most of the types of magnetotactic bacteria described in this paper have already been detected (LINSDE BARROSand ESQUIVEL 1985), but only one species - Aquaspirillum magnetotacticurn - has been extensively studied (BLAKEMORE and FRANKEL 1989). In these studies a pure culture was obtained by cloning this microorganism, enabling not only microbiological studies, but also the determination of some of the biophysical and genetic properties of the bacteria. Although such investigations require pure culture, detailed studies of the morphological properties of the cells and investigation of their magnetic characteristics are possible using an enriched culture. As the coccoid magnetotactic bacteria made up the vast majority of Batumi lake. they wese chosen for detailed study of the organization and structure of intracellular magnetic particles. As can be seen from Fig. 2a, these microorganisms contain two chains of magnetic grains, containing 6 to 8 magnetosomes each. In nearly every cell the terminal magnetosomes are of smaller dimensions. indicating an incomplete biomineralization process. In most cells magnetic particles are located near the cell surface in two parallel curved chains, but in some cases interrupted chain parallelism can be observed (Fig. 2c), as well as the presence of three chains of magnetosomes (Fig. 2d). We are unable as yet to explain the effect of these abnormalities on the magnetic properties of the cells. However, artifacts arising during preparation for electron microscopy cannot be excluded.
190
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Fig. 5
Magnetotactic microorganism with flagellar location of magnetosomes. Bar represents 500 nm
The division of magnetotactic cells was observed in several occasions (Fig. 2e). It is clear that duplication of magnetosomes occurs first, and it is only subsequently that the cells divide into two. This sequence of events is a clear indication that the formation and organization of magnetic material in these cells is genetically determined. To investigate the magnetic characteristics, the cells were disrupted by alkaline treatment, and isolated magnetic particles were analyzed. It can be seen (Fig. 6A, curves l), that remanent saturation magnetization J,, is achieved in magnetic field H e = 200 mT, remanent acquisition coercive force H,,, = 46 mT, and remanence coercive force H,,, = 22 mT. These data characterize relatively hard ferromagnetic material and are common to single-domain interacting magnetic particles (BANERJEE and MOSKOWITZ 1985). Fig. 6B, curve 1 , represents the thermomagnetic curve for saturation magnetization J , ( T ) .The curve is of Weiss type, Curie temperature (T,) of examined material equals to 580 “C, that corresponds to pure stoichiornetric magnetite. After heating to 620 ‘C, the J , decreases twofold; the second heating curve (Fig. 6 8 , curve 2) is more direct and T, increases to 650 “C. These data indicate the partial oxidation of magnetite and formation of intermediate solid solutions with general formula F e , - , ~ , O , , where x indicates the number of cation vacancies. This material is relatively soft ferromagnetic: the saturation magnetic field of remanent magnetization is 80 mT, Hir2= 20 mT, HCrl= 20 mT (see Fig. 6A, curves 2). a-Fe,O, can be formed by oxidation process as well, nevertheless its input in magnetization is negligible. All these results strictly indicate that magnetic material of the studied magnetotactic bacterial is represented by single-domain interacting particles of pure magnetite. This investigation clearly shows that several types of magnetotactic bacteria are prevalent in some of the freshwater lakes and ponds of Georgia. Biochemical and genetic studies may yet explain the unknown mechanisms of magnetoreception and magnetotaxis. Potential
191
Magnetotactic bacteria from freshwater lakes
0
100
200
300 400
500
600
T ("Cl
Fig. 6 Magnetic parameters of magnetic grains isolated from magnetococci. a. Normalized remnent acquisition curves; determination of remnent coercive force tl,, and remnent acquisition coercive force H:, ( I - before heating, 2 - after heating up to 620 "C). b. Thermomagnetic curves J , ( T ) :1 - initial state, 2 - after heating up to 620 "C
practical applications of high-grade cheap magnetite make further studies in this field extremely worthwhile.
Acknowledgements We are grateful to Miss DAREJAN GIORHELIDZE for technical assistance. We thank Prof. TEIMURAZ CHANISIIVILI and Dr. BORISZAVIZION for helpful discussion of the work. We are thankful to PATRICK J. HILLERY for help in preparing the English version of the manuscript.
References BALKWILL, D. L., MARATEA, D. and BLAKEMORE, R. P., 1980. Ultrastructure of a magnetotactic spirillum. J. Bacteriol., 141, 399-408. BANERJEE, S. K. and MOSKOWITZ, B. M., 1985. Ferromagnetism of magnetite. In: Magnetite BioD. S. JONES and B. J. MACmineralization and Magnetoreception in Organisms (J. L. KIRSCHVINK, FADDEN. Editors), pp. 32 -63. Plenum Press, New York. BAZYLINSKI, D. A,, FRANKEL, R. B. and JANNASCH, H. W., 1988. Anaerobic magnetite production by a marine magnetotactic bacterium. Nature, 334, 518 - 51 9. BLAKEMORE, R. P., 1975. Magnetotactic bacteria. Science, 190, 377- 379. BLAKEMORE, R . P., 1982. Magnetotactic bacteria. Ann. Rev. Microbiol.. 36, 217-238. BLAKEMORE, R. P. and FRANKEL, R. B.. 1989. Biomineralization by magnetotactic bacteria. In: MetalMicrobe Interactions (R. K. POOLEand G. M. GADD,Editors), pp. 85-98. IRL Press, Oxford. R. P., MARATEA, D. and WOLFE,R. S., 1979. Isolation and pure culture of a freshwater BLAKEMORE, magnetic spirillum in chemically defined medium. J. Bacteriol., 140, 720- 729. BLAKEMORE,R. P., SHORT,K. A,, BAZYLINSKI. D. A., ROSENBLATT. C. and FRANKEL, R. B., 1985. Microaerobic conditions are required for magnetite formation within A yuuspirillurn nzugneroracticum. Geomicrobiology, 4. 53 - 7 1.
192
E. A. MATITASHVILI et al.
LINS DE BARROS,H. G . P. and ESQUIVEL. D. M. S., 1985. Magnetosensitive microorganisms discovered in muddy waters of Rio-de-Janeiro district. In: Magnetite Biomineralization and Magnetoreception in Organisms (J. L. KIRSCHVINR. D. S. JONES and B. J. MACFADDEN, Editors), pp. 383-410. Plenum Press. New York. MATSUNAGA. T. and KAMIYA. S.. 1987. Use of magnetic particles isolated from magnetotactic bacteria for enzyme immobili7ation. Appl. Microbiol. Biotechnol., 26, 328 - 332. TOWE.K . M. and MOENCH. T. T.. 1981. Electron-optical characterization of bacterial magnetite. Earth. Planett. Sci. Lett.. 52. 213-220. Mailing address: Dr. R. S. Adamia, Department of Genetic Engineering and Biotechnology, SIU “Bacteriophage”, Gotua st. 3. Tbilisi. Georgia - 380060
(Scientific-Industrial Union “Bacteriophage”, Tbilisi, Georgia - 380 060. ‘Institute of the Physics of the Earth, Academy of Sciences, Moscow - 123 810, Russia and *European Molecular Biological Laboratory, W-6900 Heidelberg, Germany)
Magnetotactic bacteria from freshwater lakes in Georgia ELWINAA. MATITASHVILI, DIANAA. MATOJAN,TATJANAS. GENDLER’,TEYMURAS V. KURZCHALIA’ a n d REVAZS. ADAMIA (Received 22 Nouernber 1991/Accepted 6 December 1991)
Several species of magnetotactic bacteria were discovered in the lakes and ponds of Georgia. Electron microscopic analysis of the bacteria showed a great variety of microbial forms as well as magnetosome arrangements. Pyramidal, cubical or hexagonal magnetic grains could be seen in different species of bacteria. The linear organization of magnetic particles was prevailing, although gathered magnetosomes were also seen. Magnetometric measurement of magnetic particles obtained from coccoid bacteria was performed. Remnent acquisition curves, as well as thermomagnetic curves of investigated material showed that the magnetosomes under study contained pure single-domain magnetite. Magnetotactic bacteria, first discovered mo r e than 15 years ago by BLAKEMORE (1975), still remain one of the most intriguing organisms of the microbial world. In the years since their discovery several groups o f scientists have studied some of the biochemical a nd morphophysiological properties of these bacteria. These studies have determined several
of the basic characteristics of these microorganisms (BALKWILL et at. 1980, BLAKEMORE 1982, T o w a n d MOENCH1981). However, a number of the most interesting and important questions still remain unanswered: What is the transportation mechanism of the iron ions f r o m the surrounding medium into the bacterial cells? How are the number and dimensions of the ferromagnetic domains determined? What determines the location of the locomotion system such that nearly all the cells in a given population move in the same direction? The most important factor-hindering progress in the study of magnetotactic bacteria is the fact that, until now, only one species - Aquaspirilium rnagnetotacticum - could be cloned to obtain a pure culture (BLAKEMORE et al. 1979). However, the complicated cultivation conditions f o r this spirillum are unsuitable f o r t h e production of large quantities of bacteria or bacterial magnetite for industrial purposes. These considerations spurred us t o search for new species of magnetotactic bacteria in lakes and freshwater reservoirs of Georgia.
Materials and methods The magnetotactic bacteria used were found in ponds and lakes in Georgia, with 8 out of 49 samples proving positive. The bacteria were located on the northern shores, in regions of muddy water with surface growth of reeds and algae. The mud to water ratio of the samples was 1 : 3. The samples were incubated in loosely capped bottles at room temperature and under weak illumination for one to several months to allow the magnetotactic bacteria to accumulate. Magnetotactic bacteria were collected by means of a steady magnet, using the equipment described by MATSUNACA and KAMrYA (1987). The bacteria were detected using a NICONTMD-2 microscope. Morphological studies of both bacteria and isolated magnetosomes were carried out using a JEM 1200 EX electron microscope.
186
E. A. MATITASHVILI et al.
Isolation was effected by spinning the magnetotactic cell suspension in a centrifuge and resuspending the pellet in 5 M NaOH. After 18 hours magnetic particles were spun down and washed several times in distilled water. isolated magnetic grains were mixed with MgO powder (nonmagnetic matrix) in 1 : 50 ratio and packed into a cylindrical quarts cell(s). which has an extremely low magnetic noise level (saturation remanencr magnetization approximately 4.1 x Am2/kg). Measurements of isothermal remnent magnetization (J,) acquired in fields up to 2.5 Tesla were carried out with the spinner magnetometer with sensitivity 1.6 x Am’. Saturation magnetization (J,) as a function of temperature was measured with continuous thermal demagnetization method. To avoid the effect of contamination, all the magnetic measurements were done for pure MgO powder as well.
Results and discussion Magnetotactic bacteria usually inhabit reservoirs rich in organic substances; small eutrophic lakes, ponds and muddy, swampy areas are the best environments (BLAKEMORE 1982). In the northern hemisphere most of the microorganisms in the population gather on the northern shores of reservoirs.
Fig. 1 Magnetotactic bacterium with pyramidal magnetosomes occurring in Eastern Georgia. Bar represents 700 nm
Magnetotactic bacteria from freshwater lakes
187
Fig. 2 Coccoid magnetotactic bacteria chosen for detailed study of magnetosomes structure and organization. Bar represents 500 nm
188
E. A. MATITASHVILI et al.
These factors influenced the choice of location where magnetotactic bacteria were sought. The lakes and ponds which were searched abound in organic substances, both naturally occurring and as the result of human activity. As the magnetotactic bacteria under study are microaerophiles (BLAKEMORE et al. 1985), or more rarely, obligate anaerobes (BAZYLINSKI et al. 1988), the samples were collected at a depth of 10 - 60 cm, all due precautions being observed. Experimental work led to discovery of several species of bacteria which respond to the earth magnetic field, as well as to the field generated by a small steady magnet. Morphological studies showed great variety among the magnetotactic bacteria. Bacteria isolated from one of the lakes in eastern part of Georgia (Fig. l), are rod shaped and have one chain of magnetic grains. These particles are pyramidal in shape, with a base of 50 nm x 50 nm, and a height of 150 nm. BLAKEMORE (1982) noted the occurrence of such bacteria in the southern hemisphere, in New Zealand. Samples taken from a natural pond in the Pioneer Park in Batumi proved extremely rich in magnetotactic bacteria. Surprisingly, water samples of this reservoir contained several different species of magnetotactic microorganisms. Prevailing part of the magnetotactic microphlore consisted of coccoid bacteria (Fig. 2a). which possess well-developed, polarly located flagellar motor system (Fig. 2b). These microorganisms contain two chains of magnetic particles of almost cubical form, with dimensions 80 nm x 80 nm x 100 nm. Considerably less amounts of rod-shaped magnetotactic bacteria were discovered in the same pond (Fig. 3). These microorganisms also contained magnetic particles arranged as a chain. Such an arrangement makes biological sense, as it significantly increases the total magnetic moment of the bacterial cells (BLAKEMORE 1982). However, in the same pond the magnetotactic bacteria were discovered in which the magnetic particles were not arranged as a chain but gathered in groups in distinct parts of the cells (Fig. 4). It seems, that the
Fig. 3 Rod-shaped bacteria with linear arrangement of magnetosomes. Bar represents 500 nm
Magnetotactic bacteria from freshwater lakes
189
Fig. 4 Non-linear organization of magnetosomes in magnetotactic bacterial cells. Bar represents 500 nm
arrangement of magnetic particles is determined by the bacterial cell itself, but does not depend on the applied magnetic field. The arrangement of magnetic particles in flagellar-like structures was striking (Fig. 5). To our mind, such location of magnetic particles has not been detected earlier. Most of the types of magnetotactic bacteria described in this paper have already been detected (LINSDE BARROSand ESQUIVEL 1985), but only one species - Aquaspirillum magnetotacticurn - has been extensively studied (BLAKEMORE and FRANKEL 1989). In these studies a pure culture was obtained by cloning this microorganism, enabling not only microbiological studies, but also the determination of some of the biophysical and genetic properties of the bacteria. Although such investigations require pure culture, detailed studies of the morphological properties of the cells and investigation of their magnetic characteristics are possible using an enriched culture. As the coccoid magnetotactic bacteria made up the vast majority of Batumi lake. they wese chosen for detailed study of the organization and structure of intracellular magnetic particles. As can be seen from Fig. 2a, these microorganisms contain two chains of magnetic grains, containing 6 to 8 magnetosomes each. In nearly every cell the terminal magnetosomes are of smaller dimensions. indicating an incomplete biomineralization process. In most cells magnetic particles are located near the cell surface in two parallel curved chains, but in some cases interrupted chain parallelism can be observed (Fig. 2c), as well as the presence of three chains of magnetosomes (Fig. 2d). We are unable as yet to explain the effect of these abnormalities on the magnetic properties of the cells. However, artifacts arising during preparation for electron microscopy cannot be excluded.
190
E. A. MATITASHVILI et al.
Fig. 5
Magnetotactic microorganism with flagellar location of magnetosomes. Bar represents 500 nm
The division of magnetotactic cells was observed in several occasions (Fig. 2e). It is clear that duplication of magnetosomes occurs first, and it is only subsequently that the cells divide into two. This sequence of events is a clear indication that the formation and organization of magnetic material in these cells is genetically determined. To investigate the magnetic characteristics, the cells were disrupted by alkaline treatment, and isolated magnetic particles were analyzed. It can be seen (Fig. 6A, curves l), that remanent saturation magnetization J,, is achieved in magnetic field H e = 200 mT, remanent acquisition coercive force H,,, = 46 mT, and remanence coercive force H,,, = 22 mT. These data characterize relatively hard ferromagnetic material and are common to single-domain interacting magnetic particles (BANERJEE and MOSKOWITZ 1985). Fig. 6B, curve 1 , represents the thermomagnetic curve for saturation magnetization J , ( T ) .The curve is of Weiss type, Curie temperature (T,) of examined material equals to 580 “C, that corresponds to pure stoichiornetric magnetite. After heating to 620 ‘C, the J , decreases twofold; the second heating curve (Fig. 6 8 , curve 2) is more direct and T, increases to 650 “C. These data indicate the partial oxidation of magnetite and formation of intermediate solid solutions with general formula F e , - , ~ , O , , where x indicates the number of cation vacancies. This material is relatively soft ferromagnetic: the saturation magnetic field of remanent magnetization is 80 mT, Hir2= 20 mT, HCrl= 20 mT (see Fig. 6A, curves 2). a-Fe,O, can be formed by oxidation process as well, nevertheless its input in magnetization is negligible. All these results strictly indicate that magnetic material of the studied magnetotactic bacterial is represented by single-domain interacting particles of pure magnetite. This investigation clearly shows that several types of magnetotactic bacteria are prevalent in some of the freshwater lakes and ponds of Georgia. Biochemical and genetic studies may yet explain the unknown mechanisms of magnetoreception and magnetotaxis. Potential
191
Magnetotactic bacteria from freshwater lakes
0
100
200
300 400
500
600
T ("Cl
Fig. 6 Magnetic parameters of magnetic grains isolated from magnetococci. a. Normalized remnent acquisition curves; determination of remnent coercive force tl,, and remnent acquisition coercive force H:, ( I - before heating, 2 - after heating up to 620 "C). b. Thermomagnetic curves J , ( T ) :1 - initial state, 2 - after heating up to 620 "C
practical applications of high-grade cheap magnetite make further studies in this field extremely worthwhile.
Acknowledgements We are grateful to Miss DAREJAN GIORHELIDZE for technical assistance. We thank Prof. TEIMURAZ CHANISIIVILI and Dr. BORISZAVIZION for helpful discussion of the work. We are thankful to PATRICK J. HILLERY for help in preparing the English version of the manuscript.
References BALKWILL, D. L., MARATEA, D. and BLAKEMORE, R. P., 1980. Ultrastructure of a magnetotactic spirillum. J. Bacteriol., 141, 399-408. BANERJEE, S. K. and MOSKOWITZ, B. M., 1985. Ferromagnetism of magnetite. In: Magnetite BioD. S. JONES and B. J. MACmineralization and Magnetoreception in Organisms (J. L. KIRSCHVINK, FADDEN. Editors), pp. 32 -63. Plenum Press, New York. BAZYLINSKI, D. A,, FRANKEL, R. B. and JANNASCH, H. W., 1988. Anaerobic magnetite production by a marine magnetotactic bacterium. Nature, 334, 518 - 51 9. BLAKEMORE, R. P., 1975. Magnetotactic bacteria. Science, 190, 377- 379. BLAKEMORE, R . P., 1982. Magnetotactic bacteria. Ann. Rev. Microbiol.. 36, 217-238. BLAKEMORE, R. P. and FRANKEL, R. B.. 1989. Biomineralization by magnetotactic bacteria. In: MetalMicrobe Interactions (R. K. POOLEand G. M. GADD,Editors), pp. 85-98. IRL Press, Oxford. R. P., MARATEA, D. and WOLFE,R. S., 1979. Isolation and pure culture of a freshwater BLAKEMORE, magnetic spirillum in chemically defined medium. J. Bacteriol., 140, 720- 729. BLAKEMORE,R. P., SHORT,K. A,, BAZYLINSKI. D. A., ROSENBLATT. C. and FRANKEL, R. B., 1985. Microaerobic conditions are required for magnetite formation within A yuuspirillurn nzugneroracticum. Geomicrobiology, 4. 53 - 7 1.
192
E. A. MATITASHVILI et al.
LINS DE BARROS,H. G . P. and ESQUIVEL. D. M. S., 1985. Magnetosensitive microorganisms discovered in muddy waters of Rio-de-Janeiro district. In: Magnetite Biomineralization and Magnetoreception in Organisms (J. L. KIRSCHVINR. D. S. JONES and B. J. MACFADDEN, Editors), pp. 383-410. Plenum Press. New York. MATSUNAGA. T. and KAMIYA. S.. 1987. Use of magnetic particles isolated from magnetotactic bacteria for enzyme immobili7ation. Appl. Microbiol. Biotechnol., 26, 328 - 332. TOWE.K . M. and MOENCH. T. T.. 1981. Electron-optical characterization of bacterial magnetite. Earth. Planett. Sci. Lett.. 52. 213-220. Mailing address: Dr. R. S. Adamia, Department of Genetic Engineering and Biotechnology, SIU “Bacteriophage”, Gotua st. 3. Tbilisi. Georgia - 380060
