Mucosal glycan degradation of the host by the gut microbiota

Abstract

The gut microbiota plays a major role in human health and an alteration in gut microbiota structure and function has been implicated in several diseases. In the colon, mucus covering the epithelium is critical to maintain a homeostatic relationship with the gut microbiota by harboring a microbial community at safe distance from the epithelium surface. The mucin glycans composing the mucus layer provide binding sites and a sustainable source of nutrients to the bacteria inhabiting the mucus niche. Access to these glycan chains requires a complement of glycoside hydrolases (GHs) produced by bacteria across the phyla constituting the human gut microbiota. Due to the increased recognition of the role of mucus-associated microbes in human health, how commensal bacteria breakdown and utilize host mucin glycans has become of increased interest and is reviewed here. This short review provides an overview of the strategies evolved by gut commensal bacteria to access this rich source of the nutrient with a focus on the GHs involved in mucin degradation.

Keywords: glycosylation; gut microbiota; mucin; mucus.

Fig. 1

Specificity of bacterial GHs and sulfatases. A hypothetical mucin glycan is depicted with monosaccharide symbols following the symbol nomenclature for glycans (Varki et al., 2015). Linkages are shown with black text and GHs are shown in red text.