Synthrophic interactions between Bacteroides and Bifidobacterium on yeast beta-glucan

Abstract

The Human Gut Microbiota (HGM) comprises two major phyla, the Bacteroidetes and Firmicutes, although important members of the Actinobacteria (Bifidobacterium) and Verrucomicrobia (Akkemansia) also make an important contribution to this ecosystem. Accumulating datasupport the notionthat the HGM can be modulated by probiotics and prebiotics to prevent or revert common diseases of the gastrointestinal tract (GIT) such as Inflammatory Bowel Disease. Because it is believed that these GIT diseases are linked to the fact that current Western populations follow a more fat-based diet, significant efforts have been made to search for novel prebiotics/probiotics in order to restore and improve gut health. So far, no publications have described probiotic properties of Bacteroidetes. Nonetheless, a case can be made that certain Bacteroides species present primary glycan degraders that interact in a syntrophic manner with other members of the microbiota, such as bifidobacteria, which are considered beneficial members of the microbiota. In this study, we present the simbiotic interactions between Bacteroides and Bifidobacterium spp. acting on yeast beta-glucan (1,3/1,6 mixed linkage beta-glucan). Bacteroides cellulosilyticus and Bacteroides ovatus act as keystone organism to share beta-1,3/1,6-glucooligosaccharides with other members of the HGM, including Bifidobacterium breve UCC2003 and Bifidobacterium bifidum. We show in these Bifidobacterium spp. a specific beta-1,3-glucosidase, which degrade some of these sharing oligosaccharides. Also, we have identified the specific sugar symporter, which incorporate these oligosaccharides into the cytoplasm of B. breve UCC2003. With the help of RT-qPCR, we have quantified and monitored how these two members of the HGM are able to symbioticly use this dietary glycan.