Novel ecological niche of Cetobacterium somerae, an anaerobic bacterium in the intestinal tracts of freshwater fish

Abstract

Aims: This study was conducted to clarify the taxonomic status of Bacteroides type A strains with high vitamin B12‐producing ability that is widely distributed in the intestinal tracts of freshwater fish. Methods and Results: Seventeen strains of Bacteroides type A isolated from five fish species were all rod‐shaped and gram‐negative. The strains were positive for esculin hydrolysis, nitrate reduction, resistance to bile, acid phosphatase, and negative for the production of catalase and urease and the susceptibility to vancomycin. The G+C content of DNA from the 17 strains was 29·1–31·9 mol%, and 16S rDNA sequence analysis revealed a close phylogenetic relationship between Bacteroides type A strains and Cetobacterium somerae sharing 99·7–100% sequence similarity. In addition, strains were capable of producing vitamin B12 at a rate of 1·82–13·98 ng ml−1 in 48 h. Conclusion: Phenotypic and phylogenetic characteristics indicated that all isolates previously classified as Bacteroides type A strains belong to C. someare. Significance and Impact of the Study: This study provided the important finding of novel niche of vancomycin‐resistant bacteria such as C. somerae in the intestinal tract of freshwater fish.

Gut content microbiota of introduced bigheaded carps ( Hypophthalmichthys spp.) inhabiting the largest shallow lake in Central Europe

“…Aeromonas and Shewanella) bacteria were frequently detected. These bacteria were found in the intestines of different other fish species too (Sugita et al, 1991;Sugita et al, 1995;Tsuchiya et al, 2008;Li et al, 2014;Ye et al, 2014;Pekala et al, 2015). Moreover, unique taxa (e.g.…”

Divergence across diet, time and populations rules out parallel evolution in the gut microbiomes of Trinidadian guppies

“…For instance, guppies categorized to enterotype 1 were estimated to have the greatest relative proportion of their metagenomes devoted to vitamin biosynthesis. Interestingly, the bacterium characterizing enterotype 1 was classified as Cetobacterium somerae, a B-12 vitamin-producing, obligate anaerobe found in several freshwater fish including zebrafish, goldfish, carp, tilapia and ayu (Sakata et al, 1981;Sugita et al, 1991;Tsuchiya et al, 2008;Roeselers et al, 2011). Other functional differences between enterotypes found in our study, including carbohydrate and amino-acid metabolism, are of likely nutritional or digestive relevance to guppy hosts, and more direct studies on functional implications of taxonomic differences in fish gut microbiomes may help elucidate their roles.…”

Evidence for a core gut microbiota in the zebrafish

“…Our 16S rRNA clone library sequences identified members of the g-Proteobacteria and Fusobacteria classes as common members of the gut microbiota in adult zebrafish raised in different locations as well as in other fish species (Figure 2). The nature of our study required that we limited our UniFrac analysis to those fish species for which complete (that is, nondereplicated) 16S rRNA clone libraries were available (Table 1), however, these same bacterial classes have been also observed in the intestinal microbiotas of other teleost fishes in culture-independent and culture-based surveys (Huber et al, 2004;Romero and Navarrete, 2006;Kim et al, 2007;Tsuchiya et al, 2008;Merrifield et al, 2009;Navarrete et al, 2009Navarrete et al, , 2010. This suggests that these specific bacterial groups are especially well adapted for the environment within the fish intestine, despite large evolutionary and geographic distances between their fish hosts.…”

“…C. somerae (initially named Bacteroides type A) is a microaerotolerant, nonspore-forming, rod-shaped, vitamin B 12 (cobalamin) producing Fusobacterium that has been shown to be indigenous to the digestive tract of multiple freshwater fish species that do not require dietary supplements of vitamin B 12 (Sugita et al, 1991;Tsuchiya et al, 2008). C. somerae was not detected in the digestive tract of two freshwater fish species, which show deficiency symptoms when fed vitamin B 12 -depleted diets (Sugita et al, 1991), suggesting that C. somerae may be involved in determining the vitamin B 12 requirements of freshwater fish.…”