Figure 1.

Bacterial activities in the colonic mucus layer environment. The colonic epithelium is covered by a mucus gel layer formed of glycoproteins called mucins. (A) Mucins consist of a protein core and a high number of O-linked glycans. They are secreted by goblet cells and are assembled into a net-like structure that forms a dense inner layer, firmly attached to cells, that does not allow bacteria to penetrate. Further from the epithelium, the outer layer becomes loose and permissive, providing a niche for intestinal bacteria. (B) Mucus oligosaccharides can act as adhesion sites for bacteria, facilitating their colonization. Some bacteria are able to form microcolonies and biofilms. (C) Bacteria with mucolytic activity can release monosaccharides from mucin O-glycans and metabolize them. These sugars can also be utilized by nearby bacteria. (D) Mucus components can influence the behavior of pathogenic bacteria by increasing or decreasing their virulence expression, adhesion, motility, proliferation, or growth.