Summer Meeting 2013: growth and physiology of bifidobacteria.

Journal of Applied Microbiology ISSN 1364-5072

REVIEW ARTICLE

Summer Meeting 2013: growth and physiology of bifidobacteria re and F. Leroy L. De Vuyst, F. Moens, M. Selak, A. Rivie Research Group of Industrial Microbiology and Food Biotechnology, Vrije Universiteit Brussel, Brussels, Belgium

Keywords arabinoxylan-oligosaccharides, bifidobacteria, cross-feeding, inulin-type fructans. Correspondence Luc De Vuyst, Research Group of Industrial Microbiology and Food Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium. E-mail: [email protected] 2013/1781: received 30 August 2013, revised 15 November 2013 and accepted 22 November 2013 doi:10.1111/jam.12415

Summary Bifidobacteria are a minor fraction of the human colon microbiota with interesting properties for carbohydrate degradation. Monosaccharides such as glucose and fructose are degraded through the bifid shunt, a dedicated pathway involving phosphoketolase activity. Its stoechiometry learns that three moles of acetate and two moles of lactate are produced per two moles of glucose or fructose that are degraded. However, deviations from this 3 : 2 ratio occur, depending on the rate of substrate consumption. Slower growth rates favour the production of acetate and pyruvate catabolites (such as formate) at the cost of lactate. Interestingly, bifidobacteria are capable to degrade inulintype fructans (ITF) (oligofructose and inulin) and arabinoxylanoligosaccharides (AXOS). Beta-fructofuranosidase activity enables bifidobacteria to degrade ITF. However, this property is strain-dependent. Some strains consume both fructose and oligofructose, with different preferences and degradation rates. Small oligosaccharides (degree of polymerization or DP of 2–7) are taken up, in a sequential order, indicating intracellular degradation and as such giving these bacteria a competitive advantage towards other inulin-type fructan degraders such as lactobacilli, bacteroides and roseburias. Other strains consume long fractions of oligofructose and inulin. Exceptionally, oligosaccharides with a DP of up to 20 (long-chain inulin) are consumed by specific strains. Also, the degradation of AXOS by a-arabinofuranosidase and b-xylosidase is strain-dependent. Particular strains consume the arabinose substituents, whether or not together with a consumption of the xylose backbones of AXOS, either up to xylotetraose or higher and either extra- or intracellularly. The production of high amounts of acetate that accompanies inulin-type fructan degradation by bifidobacteria cross-feeds other colon bacteria involved in the production of butyrate. However, bifidobacterial strain-dependent differences in prebiotic degradation indicate the existence of niche-specific adaptations and hence mechanisms to avoid competition among each other and to favour coexistence with other colon bacteria.

Introduction The human colon is a metabolically very active organ. Moreover, human colon fermentation is a very complex process. It encompasses the degradation of nondigestible compounds, both diet- and host-derived, carried out by highly interactive anaerobic microbial communities that display saccharolytic and/or proteolytic activities (Flint et al. 2012; Scott et al. 2013). However, there is consider-

able evidence that Western-type diets with high intakes of meat, fat, and simple carbohydrates, and with low intakes of nondigestible carbohydrates are positively related to several disorders such as constipation, obesity, inflammatory bowel disease and colon cancer (Koropatkin et al. 2012; Macfarlane and Macfarlane 2012; Windey et al. 2012; de Wouters et al. 2012; Everard and Cani 2013). The type of fermentation, carbohydrate vs protein fermentation, has a major impact on the metabolite output

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of the colon microbiota and hence on the physiology and health of the colon. In the proximal colon, where mainly carbohydrate fermentation takes place by saccharolytic micro-organisms, a low luminal pH and the production of beneficial short-chain fatty acids (SCFAs; acetate, butyrate and propionate) occur (Flint 2004; Grootaert et al. 2007; Falony and De Vuyst 2009; Flint et al. 2012; Nyangale et al. 2012). In contrast, the distal colon is dominated by protein fermentation carried out by proteolytic micro-organisms and a higher luminal pH as well as the formation of undesirable and potentially toxic end-products such as ammonia, branched SCFAs, amines and phenols occurs (Falony and De Vuyst 2009; Macfarlane and Macfarlane 2012; Richardson et al. 2013). Alternatively, the abundance of dietary and endogenous glycans and polysaccharides, which vary in chemical structure immensely, shape the human colon microbiota (Koropatkin et al. 2012). To reduce the fermentation of proteins by colon bacteria, carbohydrate fermentation may be extended towards the distal colon, for instance through slower fermentation of more complex polysaccharides taken up through diet (Van Craeyveld et al. 2008; Grootaert et al. 2009; Sanchez et al. 2009). Based on their metabolism, some members of the colon microbiota have received particular attention because of their dedicated fermentation potential and possible health-promoting properties. For instance, certain strains of Bifidobacterium species can be considered as intestinal health markers. Bifidobacteria are Gram-positive, anaerobic, saccharolytic Actinobacteria with a fermentative metabolism; they mainly occur in the gastrointestinal tract of mammals and insects, but are also present in sewage, the oral cavity and water kefir (Ventura et al. 2010; Gulitz et al. 2013). These micro-organisms represent a minor fraction of the human colon microbiota whose population composition varies considerably during life (Matamoros et al. 2013). The highest bifidobacterial proportion in the colon (up to 90% of the total colon microbiota) occurs during the first 12 months of life (Tannock 2010). This abundance significantly decreases over time to DP 4–5 > DP 6–7, which indicates a preferential degradation of short chains of oligofructose without the release of free fructose into the medium (Fig. 3a). However, these strains consume fructose at a faster rate than oligofructose. Bifidobacterial strains that belong to cluster C (four strains from three species) consume fructose and oligofructose and even perform a partial degradation of longchain inulin. Oligofructose is degraded extracellularly, because of the size of the oligofructose fractions tackled, as all these fractions are consumed simultaneously with a concomitant release of fructose into the medium. However, oligofructose is consumed at a substantial faster rate than fructose. A fourth group, cluster D (two strains from two species), is composed of bifidobacteria that perform a fast degradation of both fructose and oligofructose. Strains belonging to this cluster also partially degrade long-chain inulin. None of the bifidobacterial strains studied are capable of degrading all fractions of long-chain inulin. To the authors’ knowledge, up to now, Bif. longum subsp. longum LMG 11047 and Bifidobacterium thermophilum LMG 11574, both strains belonging to


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Figure 3 Preferential (left) and nonpreferential (right) degradation of short fractions of oligofructose by Bifidobacterium longum subsp. longum BB536 and Bacteroides thetaiotaomicron LMG 11262, respectively. ( ) F6; ( ) GF5; ( ) F5; ( ) GF4; ( ) F4; ( ) F3; ( ) F2 and ( ) Fructose.

cluster D, perform the most efficient degradation of longchain inulin, up to an estimated DP of 20 (Fig. 4; Falony et al. 2009a). As the ITF degradation capacity of bifidobacteria is strain-dependent, the bifidogenic effect of ITF in the colon cannot be attributed to the bifidobacterial colon population as a whole. Therefore, the intracellular degradation of oligofructose by strains belonging to cluster B could be a competitive advantage towards other colon bacteria, because no free fructose is released by these bifidobacteria that may serve as an easy energy source for competing micro-organisms. Indeed, oligofructose degradation by Bacteroides spp., Lactobacillus spp., Roseburia spp., Eu. rectale and F. prausnitzii occurs extracellularly and nonselectively (Fig. 3b), which makes these bacteria less competitive than ITF-consuming bifidobacteria (Makras et al. 2005; Van der Meulen et al. 2006a,b; Falony et al. 2009b; Moens, Riviere, Weckx, De Vuyst, unpublished results). However, oligofructose degradation by bifidobacterial strains belonging to clusters C and D

also occurs extracellularly, but at a rate that secures their enhanced competitiveness. Indeed, co-culture fermentations with a representative strain of each of the four bifidobacterial clusters and Bacteroides thetaiotaomicron LMG 11262, a strain that is able to degrade oligofructose and long-chain inulin, show a different degree of competition. Bifidobacteria of cluster A are completely dominated by Bact. thetaiotaomicron LMG 11262. Bifidobacteria of cluster B are able to dominate the co-culture fermentations, once oligofructose and short fractions of long-chain inulin become available in the medium, thanks to the nonpreferential extracellular degradation of long-chain inulin by Bact. thetaiotaomicron LMG 11262. Bifidobacteria belonging to clusters C and D are dominant throughout the co-culture fermentations due to their very efficient consumption of oligofructose and short fractions of longchain inulin. A co-cultivation on medium containing long-chain inulin as an energy source of the highly competitive strain Bif. longum subsp. longum LMG 11047 with Roseburia inulinivorans DSM 16841T, a butyrate

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Figure 4 Partial breakdown of long-chain inulin by Bifidobacterium longum subsp. longum LMG 11047 (cluster D). The vertical line represents a degree of polymerization (DP) of 20.


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producer that is able to degrade oligofructose and longchain inulin, prevents butyrate production by the latter (Falony et al. 2009c). Similarly, a co-cultivation of Bif. longum subsp. longum LMG 11047 with either F. prausnitzii DSM 17677T on oligofructose or inulin, or Eu. rectale CIP 105953T on oligofructose, indicates lack of competitiveness of the butyrate-producing colon bacteria towards Bif. longum LMG 11047 (Moens, Riviere, Weckx, De Vuyst, unpublished results). This high fitness of certain Bif. longum strains may explain the observed dominance of Bif. longum among the bifidobacterial communities present in the human colon (Mangin et al. 2006; Ramirez-Farias et al. 2009; Turroni et al. 2009, 2013; Matamoros et al. 2013). Alternatively, the rate at which ITF are degraded may determine their abundance towards the distal colon (Van den Abbeele et al. 2011). The strain-dependent differences in ITF consumption patterns and preferences suggest that different bifidobacterial strains get specialized in the degradation of certain chains of these complex prebiotics, indicating that clusters of bifidobacterial strains could avoid competition among each other and with other ITF-degrading colon

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AX consist of a linear backbone of 1500–15 000 b-(1?4)linked xylose units, randomly substituted with arabinose at the C-(O)-2 or C-(O)-3 positions (monosubstituted) or on both the C-(O)-2 and C-(O)-3 positions (disubstituted), with glucuronic acid at the C-(O)-2 positions or acetylgroups at the C-(O)-2 and/or C-(O)-3 positions, resulting in various AX molecules (Fig. 2b). Arabinose units can in turn be esterified with ferulic acid and p-coumaric acid at the C-(O)-5 positions (Izydorczyk and Biliaderis 1995; Lequart et al. 1999; Schooneveld-Bergmans et al. 1999). XOS can be considered as unsubstituted xylose backbones (Broekaert et al. 2011). On an industrial scale, AXOS and XOS are generated through the enzymatic cleavage of AX with endoxylanases, resulting in various molecules differing

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Figure 5 Possible cooperations between the different clusters of bifidobacterial strains regarding their capacity to degrade inulin-type fructans (ITF) (a) and xylo-oligosaccharides (XOS) and arabinoxylan-oligosaccharides (AXOS) (b). The release of partial carbohydrate breakdown products [fructose, arabinose, xylose, and XOS (xylose backbones)] in the medium by bifidobacterial strains belonging to one cluster opens cross-feeding opportunities with other bifidobacterial strains belonging to other clusters. Grey and white boxes represent unused and used substrates, respectively. Arrows indicate cross-feeding of oligofructose (—), long-chain inulin (‐‐‐) and fructose (…..) between the clusters of bifidobacterial strains degrading ITF (a) and cross-feeding of arabinose substituents (—), xylose backbones (‐‐‐) and monosaccharides (…..) between the clusters of bifidobacterial strains degrading XOS and AXOS (b).


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in DP (ranging between 3 and 67) and degree of substitution (arabinose/xylose ratios between 025 and 069) (Broekaert et al. 2011). Several in vivo and in vitro studies have shown that AXOS (Grootaert et al. 2007; Van Craeyveld et al. 2008; Cloetens et al. 2010; Broekaert et al. 2011) and XOS (Campbell et al. 1997; Rycroft et al. 2001; Hsu et al. 2004; Aachary and Prapulla 2010; M€akel€ainen et al. 2010; Madhukumar and Muralikrishna 2012) are bifidogenic. This bifidogenic effect is strongly influenced by the complexity of the AXOS and XOS molecules and decreases with increasing average DP and degree of substitution (Grootaert et al. 2007; Aachary and Prapulla 2010; Pollet et al. 2012). Genome sequence analysis reveals that several bifidobacterial strains contain genes possibly coding for enzymes involved in the debranching of side groups (a-arabinofuranosidases, glucuronidases, acetyl esterases and feruloyl esterases) and in the cleavage of the xylose backbones of AXOS and XOS (b-endoxylanases, b-xylosidases, and b-exoxylanases) (Schell et al. 2002; van den Broek et al. 2008). To study the degradation kinetics of AXOS, methods need to be applied that can deal with the complex structures, difficult chromatographic separation and laborious identification of AXOS (Riviere et al. 2013). In the past, only bacterial growth and SCFA production were measured (Van Laere et al. 2000; Crittenden et al. 2002) or fermentations were performed on purified AXOS standards (Pastell et al. 2009). Lately, a new analytical method has been developed through HPAEC-PAD that offers structural information, without the need for accompanying spectroscopic techniques or standards, to quickly characterize AXOS degradation during fermentation by colon bacteria (Riviere et al. 2013). It involves the application of a-arabinofuranosidase enzymes that can distinguish between mono- and disubstituted xylose residues of the xylose backbone of AXOS, which allows the identification of different peaks in the AXOS degradation patterns. To establish the so-called AXOS degradation fingerprints of bifidobacterial strains (consumption of arabinose, xylose, XOS and xylose backbones of AXOS, and AXOS as a function of time), a combination of chromatographic methods has been applied, namely HPAEC-PAD with a column consisting of medium-sized stationary phase particles (for the quantitative determination of arabinose, xylose and XOS) and HPAEC-PAD with a column consisting of small-sized stationary phase particles (for the qualitative determination of AXOS breakdown). A comparative statistical study of these fingerprints of 36 different bifidobacterial strains, belonging to eleven different species, led to the identification of five clusters of strains differing in their nature and mechanism of AXOS breakdown (Fig. 5b; Riviere et al. 2014). 484

A first cluster of 15 strains from seven species do not use XOS neither AXOS but can grow on monosaccharides (whether or not including arabinose and xylose). Cluster II strains (eight strains from one species) consume arabinose from AXOS, both mono- and disubstituted, which results in the release of unsubstituted xylose backbones of AXOS in the medium (they do not use XOS), indicating an extracellular arabinose substituent-oriented AXOS metabolism. Clusters III (ten strains from six species) and IV strains (two strains from one species) consume XOS and the xylose backbones of AXOS (after cleaving off the arabinose), both only up to xylotetraose, which indicates preferential degradation. Similarly, it has been shown through rat experiments that mainly AXOS with a low average DP exhibit a bifidogenic effect (Van Craeyveld et al. 2008). An in vitro study with Bif. adolescentis DSM 20083 and Bif. longum DSM 20097 showed that the degree of XOS consumption decreases when the average DP of the XOS substrates increases from 3–4 to 5–6 (Moura et al. 2007). In vitro fermentation of XOS by a Bif. adolescentis strain also showed that low-DP XOS (xylobiose and xylotriose) are the preferred substrates (Wang et al. 2010). Cluster III strains only use a limited set of the various AXOS molecules, which is not accompanied by an increase of xylose backbones of AXOS in the medium, suggesting the presence of highly specific a-arabinofuranosidases. Cluster IV strains use a broad set of AXOS molecules, probably due to the presence of various a-arabinofuranosidases, which involves an initial increase in XOS in the medium. It is worth to notice that Bif. longum subsp. longum LMG 11047, an efficient degrader of both oligofructose and long-chain inulin (Falony et al. 2009a), belongs to cluster IV. Cluster V strains (one strain) show a similar arabinose substituent degradation profile as that of strains belonging to clusters II and IV and use XOS and xylose backbones of AXOS up to xylohexaose, and possibly longer XOS molecules (which were not measured), indicating a nonpreferential degradation mechanism. The possibility of a degradation of XOS with a DP up to six has also been shown for two Bif. adolescentis strains (Wang et al. 2010; Amaretti et al. 2013). The consumption of XOS and the xylose backbones of AXOS either results in an increase in xylose in the medium, indicating extracellular breakdown, or no xylose accumulation, indicating intracellular transport and breakdown of XOS. Extracellular XOS degradation with the release of xylose in the medium has been shown for other bifidobacteria too (Jaskari et al. 1998; Pastell et al. 2009; Gilad et al. 2010; Amaretti et al. 2013). It is thought to be a competitive disadvantage compared to intracellular degradation (Crittenden et al. 2002; Van der Meulen et al. 2004, 2006a; Falony et al. 2009a; De Vuyst and Leroy 2011).


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The strain-dependent differences in AXOS and XOS consumption patterns suggest that different bifidobacterial strains get specialized in the degradation of certain constituents of these complex prebiotics, indicating that clusters of bifidobacterial strains could avoid competition among each other or, more importantly, even could coexist whether or not through cooperation by degrading AXOS and XOS (Fig. 5b). For instance, in a triculture of Bif. longum ATCC 15707, Bif. adolescentis ATCC 15703 and Bif. breve ATCC 15700, cross-feeding takes place when these strains are grown on AXOS (Pastell et al. 2009). This kind of specialization together with the potential to degrade xylose backbones intracellularly could explain the selective growth stimulation of bifidobacteria by AXOS and XOS. Cross-feeding mechanisms As mentioned above, one of the remarkable effects of ITF feeding to the human colon microbiota is an increase in the bifidobacterial proportion of the colon microbiota. This bifidogenic effect is generally accompanied by a butyrogenic effect or a rise in butyrate production in the colon. However, it is clear that bifidobacteria are not able to produce butyrate through ITF consumption, as reflected by their genomes (Klijn et al. 2005; Makras et al. 2005; Rossi et al. 2005; Falony et al. 2006, 2009a). An obvious explanation for the butyrogenic effect of ITF is their degradation by butyrate-producing bacteria. Whereas evidence for this was scarce in the past (Duncan et al. 2002b,c, 2003, 2006; Falony et al. 2006; Duncan and Flint 2008), recent kinetic studies have indicated that butyrate-producing bacteria are indeed able to degrade ITF (Falony et al. 2009c). Based on a study of the ITF degradation fingerprints of five butyrate-producing bacteria (Anaerostipes caccae DSM 14662T, Roseburia faecis

DSM 16840T, Roseburia hominis DSM 16839T, R. inulinivorans DSM 16841T and Roseburia intestinalis DSM 14610T), genus- and species-dependent variations have been found (Falony et al. 2009c). Whereas A. caccae DSM 14662T and R. hominis DSM 16839T do not degrade oligofructose neither long-chain inulin and only grow on fructose, both R. faecis DSM 16840T and R. intestinalis DSM 14610T degrade oligofructose but not long-chain inulin. However, R. inulinivorans DSM 16841T is capable of degrading long-chain inulin. Also, other studies have demonstrated the capacity of several F. prausnitzii strains and Eu. rectale A1-86 to utilize inulin as an energy source (Duncan et al. 2002c; Duncan and Flint 2008). Considering the fact that these butyrate-producing colon bacteria are present in high proportions in the colon (Arumugam et al. 2011; Lopez-Siles et al. 2011), with Eu. rectale and F. prausnitzii even making up 4% and 8%, respectively, of the colon microbiota of individuals consuming a Western-type diet (Flint et al. 2012; Scott et al. 2013), a rise in butyrate production upon ITF consumption does not come as a surprise. However, the butyrate-producing colon bacteria mentioned above, except for A. caccae DSM 14662T, necessitate exogenous acetate to degrade fructose (Duncan et al. 2002c; Duncan and Flint 2008; Falony et al. 2009c). This suggests the occurrence of cross-feeding interactions, whereby an initial partial hydrolysis of the polysaccharides by primary degraders, in casu bifidobacteria, provides polysaccharide breakdown products (monosaccharides and oligosaccharides) and end-metabolites (acetate and lactate) that can serve as substrates for secondary degraders, in casu butyrate-producing colon bacteria (Fig. 6; Barcenilla et al. 2000; Duncan et al. 2002a,b,c, 2004, 2006; Morrison et al. 2006; Duncan and Flint 2008; Falony and De Vuyst 2009; Mu~ noz-Tamayo et al. 2011). Two main types of cross-feeding interactions between bifidobacteria and

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butyrate-producing colon bacteria have been shown experimentally (Belenguer et al. 2006; Falony et al. 2006). In a first type of cross-feeding, partial breakdown of oligofructose by bifidobacteria releases free fructose and acetate that are used by other colon bacteria to produce butyrate; this is illustrated with a co-culture of Bif. longum subsp. longum BB536 (cluster B) and A. caccae DSM 14662T (produces butyrate out of fructose, lactate and/or acetate but does not need exogenous acetate; Falony et al. 2006) and a co-culture of Bif. adolescentis DSM 20083 and Eubacterium hallii DSM 17630 (produces butyrate out of fructose or lactate with the need of exogenous acetate; Belenguer et al. 2006). In a second type of crossfeeding, initial partial breakdown of oligofructose by bifidobacteria provides other colon bacteria with exogenous acetate that can be used to produce butyrate by growing on oligofructose simultaneously; this is illustrated with a co-culture of Bif. longum subsp. longum BB536 and R. intestinalis DSM 14610T (Falony et al. 2006). These two types of cross-feeding interactions will certainly occur between members of the colon microbiota when ITF and other dietary fibres traverse the large intestine (Flint et al. 2008, 2012; De Vuyst and Leroy 2011; Boets et al. 2013; Scott et al. 2013). However, the outcomes of these crossfeeding interactions are hard to predict and are dependent on the fermentable substrate and the bacteria involved. Indeed, whereas cross-feeding between Bif. longum subsp. longum BB536 and A. caccae DSM 14662T or R. intestinalis DSM 14610T, on oligofructose as a substrate, yields substantial amounts of butyrate, hardly any butyrate is produced in a co-culture of Bif. longum subsp. longum LMG 11047 (a very competitive bifidobacterial strain belonging to cluster D) and R. inulinivorans DSM 16841T, on long-chain inulin as a substrate (Falony et al. 2006, 2009c). This indicates that competition is an additional player during cross-feeding interactions and hence may be responsible for domination of certain colon bacteria on the available substrate (Fig. 6). This competition between resident bifidobacteria and butyrate-producing colon bacteria may explain the negligible increase in butyrate production in the colon of twelve human volunteers after ingestion of inulin (10 g day 1) over a 16-day period, in spite of a significant increase in the proportions of Bif. adolescentis and F. prausnitzii (RamirezFarias et al. 2009). Whether the production of propionate is also the result of cross-feeding is not known yet. Three different pathways are proposed, namely out of fucose (a breakdown product of mucin) through the propanediol pathway carried out by R. inulinivorans, out of succinate through the succinate pathway carried out by bacteroides, or out of lactate through the acrylate pathway carried out by members of the Veillonellaceae (Louis et al. 2007; Flint et al. 2012). 486

Conclusions Kinetic analysis of the breakdown of complex poly- and oligosaccharides, such as ITF, AXOS and XOS, reveals a phenotypical variation among bifidobacterial strains concerning their degradation capacity. However, the concomitant degradation kinetics determines the competitiveness of these strains. Further, the strain-dependent differences point towards the existence of specific niche adaptations, indicating that different bifidobacterial strains could avoid competition among each other and thus coexist in the same environment, in casu the human colon, whether or not through cooperation. Also, the butyrogenic effect caused by butyrate-producing colon bacteria is rather due to cross-feeding interactions than to direct fructan consumption. However, oligofructose consumption rates and the capacity to degrade long-chain inulin by colon bacteria play a crucial role in determining the outcome of these cross-feeding interactions. In spite of the complexity of the interactions between primary and secondary degraders, the bifidogenic and butyrogenic effects of inulin-type fructan digestion and their beneficial influence on human health and well-being remain without dispute. Whether a propionogenic effect caused by propionate-producing colon bacteria is the result of cross-feeding interactions as well has to be shown yet. Acknowledgements The authors acknowledge their financial support from the Research Council of the Vrije Universiteit Brussel (SRP, IRP, and IOF projects), the Research Foundation Flanders (FWO-Vlaanderen), and the Hercules Foundation. F.M. and A.R. are the recipients of a PhD fellowship of the FWO-Vlaanderen; M.S. is the recipient of a PhD fellowship of the Vrije Universiteit Brussel in the framework of a bilateral agreement with the University of Ljubljana. Conflict of Interest No conflict of interest declared. References Aachary, A.A. and Prapulla, S.G. (2010) Xylooligosaccharides (XOS) as an emerging prebiotic: microbial synthesis, utilization, structural characterization, bioactive properties, and applications. Compr Rev Food Sci Food Safe 10, 2–16. Amaretti, A., Bernardi, T., Tamburini, E., Zanoni, S., Lomma, M., Matteuzzi, D. and Rossi, M. (2007) Kinetics and metabolism of Bifidobacterium adolescentis MB 239 growing on glucose, galactose, lactose and galactooligosaccharides. Appl Environ Microbiol 73, 3637–3644.


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Abstracts of the Anatomical Society Summer Meeting 2013, July 4-5, 2013, Dublin, Ireland.

2013 AES Annual Meeting.

c mice.

[Meeting report -- retinal research 2013 in Germany].

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Effect of depolymerized alginates on the growth of bifidobacteria.

Best of the 2013 AUA Annual Meeting Part II: More Highlights From the 2013 American Urological Association Annual Meeting, May 4-8, 2013, San Diego, CA.

The college of podiatry annual conference 2013: meeting abstracts.

Council of Deans business meeting, July 15, 2013, Chicago, IL.

Abstracts of presentations at the 2013 northeastern division meeting.

British Association of Clinical Anatomists. Abstracts of papers presented at Summer Meeting, 1978.

Second International Meeting of ISEV 2013: Boston, USA, April 17(th)-20(th), 2013.

Abstracts of the Irish Society for Rheumatology, Autumn Meeting 2013, 19-20 September, 2013, Co.Meath, Ireland.

Bacterial physiology. Linking cell differentiation and growth.

Introduction to the World Society for Reconstructive Microsurgery 2013 meeting.

Psoriatic enthesitis: an update from the GRAPPA 2013 Annual Meeting.

GRAPPA Trainees Symposium 2013: a report from the GRAPPA 2013 Annual Meeting.

[Report from the annual meeting 2013 in Düsseldorf].

Philadelphia 2013: international consensus meeting on periprosthetic joint infection.

Abstracts of the 64th Annual Meeting of the American Association for the Study of Liver Diseases: the Liver Meeting 2013. November 1-2, 2013. Washington, D.C., USA.

Nobel 2013 Physiology or medicine: Traffic control system within cells.

Diet quality limits summer growth of field vole populations.

EJI Summer School on Advanced Immunology.

British Thoracic Society summer meeting. 11-13 July 1990, Birmingham. Abstracts.