Environmental factors drive bacterial degradation of gastrointestinal mucus.

The mucus layer lining the gastrointestinal tract is essential for gut health, providing a protective barrier while maintaining host-microbiome symbiosis. Its disruption is a hallmark of diseases like ulcerative colitis, yet how bacterial activity impacts mucus structure remains unclear. We developed a method to collect human-cell-derived mucus that mimics human colonic mucus and used it to investigate mucus degradation by commensal bacteria. Glycan foraging by species such as Bacteroides thetaiotaomicron and Bacteroides fragilis did not alter mucus rheology. Instead, secreted proteases were the primary drivers of degradation. Protease activity by B. fragilis and Bifidobacterium longum subsp. infantis was nutrient-dependent, while Enterococcus faecalis was further influenced by oxygen. Under oxidative stress, E. faecalis upregulated carbohydrate metabolism and virulence genes. These results reveal that bacterial mucus degradation is context-dependent and shaped by environmental factors. Our findings underscore the value of human cell-derived mucus models for understanding bacteria-mucus interactions in health and disease.