Metagenomic Insights into the Effects of Fructooligosaccharides (FOS) on the Composition of Luminal and Mucosal Microbiota in C57BL/6J Mice, Especially the Bifidobacterium Composition

Fructooligosaccharides (FOS) are considered prebiotics and have been proven to selectively promote the growth of Bifidobacterium in the gut. This study aimed to clarify the effects of FOS intake on the composition of luminal and mucosal microbiota in mice. Briefly, mice were fed a 0% or 25% FOS (w/w)-supplemented diet for four weeks, and the composition of luminal and mucosal microbiota, especially the Bifidobacterium, was analyzed by sequencing the V3–V4 region of 16S rRNA and groEL gene, respectively. After FOS intervention, there were significant increases in the total and wall weights of the cecum and the amount of total short-chain fatty acids (SCFAs) in the cecal contents of the mice. At the phylum level, the results showed a significant increase in the relative abundance of Actinobacteria in the contents and mucosa from the cecum to the distal colon in the FOS group. Besides Bifidobacterium, a significant increase was observed in the relative abundance of Coprococcus in all samples at the genus level, which may be partially related to the increase in butyric acid levels in the luminal contents. Furthermore, groEL sequencing revealed that Bifidobacterium pseudolongum was almost the sole bifidobacterial species in the luminal contents (>98%) and mucosa (>89%). These results indicated that FOS can selectively promote B. pseudolongum proliferation in the intestine, either in the lumen or the mucosa from the cecum to the distal colon. Further studies are required to reveal the competitive advantage of B. pseudolongum over other FOS-metabolizing bacteria and the response mechanisms of B. pseudolongum to FOS.