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

AIMS: This study was conducted to clarify the taxonomic status of Bacteroides type A strains with high vitamin B(12)-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 x 1-31 x 9 mol%, and 16S rDNA sequence analysis revealed a close phylogenetic relationship between Bacteroides type A strains and Cetobacterium somerae sharing 99 x 7-100% sequence similarity. In addition, strains were capable of producing vitamin B(12) at a rate of 1 x 82-13 x 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.     

Cetobacterium somerae sp. nov. from human feces and emended description of the genus Cetobacterium

Phenorypic and phylogenetic studies were performed on four isolates of an unidentified gram-negative, microaerotolerant, non-spore-forming, rod-shaped bacterium isolated from the feces of children. The unknown organism was bile resistant and produced acetic acid as the major end product of metabolism of peptides and carbohydrates. It possessed a low DNA G + C content of 31 mol %. Comparative 16S rRNA gene sequencing demonstrated that the four isolates were phylogenetically identical (100% 16S rRNA sequence similarity) and represent a hitherto unknown sub-line within the genus Cetobacterium. The novel bacterium displayed approximately 5% sequence divergence with Cetobacterium ceti, and can be readily distinguished from the latter by physiological and biochemical criteria. Based on phylogenetic and phenotypic evidence, it is proposed that the unknown fecal bacterium be classified in the genus Cetobacterium, as Cetobacterium somerae sp. nov. The proposed type strain of Cetobacterium somerae is WAL 14325(T) (ATCC BAA-474(T) = CCUG 46254T).     

Identification of Intracellular Bacteria in the Ciliate Balantidium ctenopharyngodoni (Ciliophora,Litostomatea)

The ciliate Balantidium ctenopharyngodoni is the most prominent protist in the guts of grass carp, where it mainly inhabits the creamy luminal contents of the hindgut. Ciliates are generally colonized by microorganisms via phagotrophic feeding. In order to study the intracellular bacteria in this ciliate, we have successfully established it in in vitro culture. Herein, we investigated and compared the bacterial community structures of cultured and freshly collected B. ctenopharyngodoni. The results showed that these two groups exhibited different bacterial communities. The most abundant bacterial family in freshly collected samples was Enterobacteriaceae, while in cultured samples it was Fusobacteriaceae. In addition, a key intracellular bacterium, Cetobacterium somerae, was identified in the cytoplasm of cultured ciliates using fluorescence in situ hybridization (FISH). This study shows that ciliates can retain the intracellular bacteria acquired in the natural habitat for quite a long time, but the bacterial community structure of ciliates eventually changes after a long period of cultivation.     

虎斑颈槽蛇肠道微生物组成和分布特征

蛇类是一种研究能量平衡的模型动物,而肠道微生物则帮助宿主获取能量和营养。大多数肠道微生物的研究集中在圈养动物上,而对于野生蛇类的研究很少。本研究从3只野生虎斑颈槽蛇（Rhabdophis tigrinus）的大肠、小肠和泄殖腔内容物提取微生物总DNA,进行16S rRNA基因V4区域扩增子测序,分析虎斑颈槽蛇肠道核心微生物组成和分布特征。结果表明,阿尔法指数在不同肠道区域的多样性不存在显著性差异。大肠、小肠和泄殖腔3个肠道部位共享534个操作分类单元（OTUs）,大肠包含最多特有OTUs（388个）。门水平,梭杆菌门（Fusobacteria）在小肠（52.87% ± 14.49%）、大肠（41.12% ± 22.60%）和泄殖腔（65.70% ± 10.44%）均为优势菌。属水平,鲸杆菌属（Cetobacterium）在小肠（46.36% ± 13.86%）、大肠（21.95% ± 9.82%）和泄殖腔（58.18% ± 14.29%）为优势菌,柠檬酸杆菌属（Citrobacter）在小肠和泄殖腔中有显著性差异。此外,在其肠道检测到很多潜在的致病菌,例如,柠檬酸杆菌属、明串珠菌属（Trichococcus）和丹毒丝菌属（Erysipelothrix）,了解了潜在致病菌在虎斑颈槽蛇肠道中的分布情况。在聚类分析中发现泄殖腔的数据重复性较好,将本研究泄殖腔数据与前人研究过的食鱼蝮（Agkistrodon piscivorus）泄殖腔高通量测序数据进行联合分析,为更广泛开展不同蛇类肠道微生物组成的差异性分析提供理论借鉴依据。