Evaluation of Bacterial Diversity and Evolutionary Dynamics of Gut Bifidobacterium longum Isolates Obtained from Older Individuals in Hubei Province, China

Bifidobacterium longum predominates in the human gut throughout the life span, from birth to old age, and could alter the intestinal microbial population and immune function in the elderly. We investigated the intestinal bacterial diversity in the elderly, and further evaluated the genetic diversity and population structure of B. longum. The results revealed a distinct difference in gut bacterial populations between the elderly from Xiangyang and its neighboring region, Enshi city. A total of 62 bifidobacterial strains were isolated, 30 of which were found to be B. longum. The multilocus sequence typing (MLST) analysis also revealed that 437 B. longum isolates from diverse regions worldwide, including the 30 isolated in this study, could be classified into 341 sequence types (STs). They could be further clustered into 10 clonal complexes and 127 singleton STs, indicating a highly genetic diversity among B. longum isolates. Two putative clone complexes (CCs) containing the isolates from Xiangyang were found to be geographically specific, and a 213-bp recombination fragment was detected. Phylogenetic trees divided these 437 isolates into three lineages, corresponding to the three subspecies of B. longum. It is noteworthy that two isolates from the elderly were identified to be B. longum subsp. suis, while the others were B. longum subsp. longum. Together, our study characterized the intestinal bacterial diversity and evolution of B. longum in the elderly, and it could contribute to further studies on the genotyping and discrimination of B. longum. IMPORTANCE Bifidobacterium longum are common inhabitants of the human gut throughout the life span, and have been associated with health-promoting effects, yet little is known about the genotype profile and evolution of these isolates. Our study showed that there was significant difference in gut bacterial community and abundance of B. longum between the elderly from two neighboring cities. Furthermore, the possible geographically specific STs, CCs, and intraspecies recombination fragment were found among the B. longum isolates from elderly.