A comprehensive review on the impact of β-glucan metabolism by Bacteroides and Bifidobacterium species as members of the gut microbiota

β-glucans are polysaccharides which can be obtained from different sources, and which have been described as potential prebiotics. The beneficial effects associated with β-glucan intake are that they reduce energy intake, lower cholesterol levels and support the immune system. Nevertheless, the mechanism(s) of action underpinning these health effects related to β-glucans are still unclear, and the precise impact of β-glucans on the gut microbiota has been subject to debate and revision. In this review, we summarize the most recent advances involving structurally different types of β-glucans as fermentable substrates for Bacteroidetes (mainly Bacteroides) and Bifidobacterium species as glycan degraders. Bacteroides is one of the most abundant bacterial components of the human gut microbiota, while bifidobacteria are widely employed as a probiotic ingredient. Both are generalist glycan degraders capable of using a wide range of substrates: Bacteroides spp. are specialized as primary degraders in the metabolism of complex carbohydrates, whereas Bifidobacterium spp. more commonly metabolize smaller glycans, in particular oligosaccharides, sometimes through syntrophic interactions with Bacteroides spp., in which they act as secondary degraders.