Comparative Genomics Of Bifidobacteirum Longum Subsp.Longum BBMN68Revealed Adaptation To Human Gastrointestinal Tract

The human intestine is the biggest microecological habitat in human body. Genus bifidobacterium is one of the most important commensal bacteria in this microecology and it has been demonstrated to exert various health benefits in human. The major factors in human gut that shape the abundance and composition of bifidobacteria include the polysaccharides, ionic constitutents and so on. Comparative genomics was proven to be a powerful tool to illuminate the mechanism by which a intestinal bacteria adapte to its surrounding environment. In this study, using Bifidobacterium longum subsp.longum BBMN68as a model strain, the special ability to adapt to the ior environment was predicted. The aresenal of glycoside hydrolysaes (GH) of bifidobacterial group was compared with that of human gut microbime with the aim to predicting the effects of this ability on the abundance of bifidobacteria.We described the features of a representative model human microbiome and bifidobacterial metagemonics, comparing their aresenal of glycoside hydrolases. We found that the distinct group have preference for different polysaccharides:Bacteroidetes for plant cell wall polysaccharides and animal polysaccharides, Firmuicutes for polysaccharides, Proteobacteria for peptidoglycans and both Actinobacteria and Bifidobacteria for starch. At the same time, bifidobacteria genomes harbored the most glycoside hydrolases for degrading starch.starch were the most universal and favorable carbon sources for bifidobacteria. The low amount of these carbon sources in adult intestine was speculated to contribute to the low relative abundance of bifidobacteria.The glycoside hydrolase and carbohydrate transport system of BBMN68was analyzed. And the genomic analysis was verified using growth experiments,2D-E and RT-PCR. The most interesting found is that it harbor the biggest number of extracellular glycoside hydrolases, the predicted substrates of which are plant cell wall polysaccharides. A cluster for degrading and fermetating [Man(GlcNAc)2] Asn, a N-glycan in mucin, was found in the genome. The pathway for degrading starch and starch hydrolysates was the only complete pathway for complex carbohydrates in human gut.It is noteworthy that all of the GH genes for degrading starch and starch hydrolysates in the BBMN68genome were conserved in all studied bifidobacterial strains.In order to investigate the genetic basis of adaptation of BBMN68to the human gut, comparative genomic analysis was carried out on BBMN68and the other24bifidobacterial genomes. The results showed that the biggest group of unique genes for carbohoydrate metabolism and transporte (COGG), for cellwall biogenesis or for replication(COGM), recombination and repair (COGL). The physiological functions involved in adaptaiton to intestinal environmtnes endowed by unique genes included degrading polysaccharides excelluarly, avoiding immun rejection by EPS, avoiding exogenous genes invading by CRISPR, acquiring K+by kdp and regulating biofilm formating by TAT.