UC Davis

Members of the mammalian gut microbiota metabolize dietary carbohydrates that are not digested by the host. While the enzymes and transporters that each strain uses to establish a nutrient niche in the gut are often exquisitely specific, the relationship between carbohydrate structure and microbial ecology is imperfectly understood. The present study takes advantage of recent advances in complex carbohydrate structure determination to test the effects of fiber monosaccharide composition on microbial fermentation. Catabolism of human milk oligosaccharides (HMOs) by the genus Bifidobacterium is reviewed to illustrate gut microbial metabolism of specific dietary fiber structures and the resulting production of acidic microbial metabolites (AMMs), such as acetic acid. In the present study, 55 fibers with varied monosaccharide composition are fermented by a pooled feline fecal inoculum in a modified MiniBioReactor array (MBRA) system over a period of 72 hours. The content of the monosaccharides glucose and xylose and the concentration of the AMMs acetic acid, propionic acid, glyceric acid, and indole-3-acetic acid are significantly associated with the reduction of pH during fermentation. Microbiome diversity and composition are also significantly associated with monosaccharide content and AMM concentration, suggesting that monosaccharide composition offers a generalizable method to compare any dietary fiber of interest and uncover unexplored links between diet, the gut microbiota, and metabolite production.