Fig. 1: The gut microbiome acts as orchestrator of the mucus barrier.
From: Slimy partners: the mucus barrier and gut microbiome in ulcerative colitis
a During homeostasis, the gut microbiome at the outer mucus layer modulates mucin production and secretion and mucus stratification mediated by HCO3− to maintain mucus barrier integrity. Dysbiosis induces impairment of the mucus barrier, accompanied by increased epithelium damage, bacterial translocation, goblet cell depletion, and host inflammation. b Gut microbiome-generated short-chain fatty acids enter colonocytes and are oxidized to generate CO2 that can be converted by carbonic anhydrase into HCO3−, which is the ideal physiological solution for precipitating calcium and raising the pH at the epithelial surface. This in turn promotes the stratification of the mucus layer. c Intestinal bacteria have evolved several strategies to adhere to the mucus barrier, including the use of adhesins, flagella, and fimbriae; achieve cross-feeding by mucin degradation; and maintain colonization resistance by means of a commensal type VI secretion system.
