Environmental factors drive bacterial degradation of gastrointestinal mucus

The mucus layer lining the gastrointestinal tract is essential for gut health, providing a protective barrier against pathogens while maintaining symbiosis with the microbiome. Its disruption is a hallmark of gastrointestinal diseases like ulcerative colitis. While glycan foraging by gut bacteria is thought to initiate mucus disruption, its impact on mucus structural properties remains poorly understood, largely due to the lack of physiologically relevant models. To address this gap, we developed a method to collect human-cell-derived mucus that closely mimics the mechanical properties of human colonic mucus. Using this system, we investigated mucus utilization and degradation by a panel of commensal bacteria with distinct metabolic profiles. Glycan utilization by species such as Bacteroides thetaiotaomicron and Bacteroides fragilis showed no correlation with changes in mucus rheology. Instead, secreted proteases were identified as the primary driver of mucus degradation. Protease activity by B. fragilis and Bifidobacterium longum was influenced by nutrient availability, whereas in Enterococcus faecalis, it was additionally affected by oxygen exposure. E. faecalis also adapted to oxidative stress by enhancing carbohydrate metabolism and upregulating several virulence genes. Together, our findings reveal that bacterial mucus degradation is context-dependent and shaped by environmental factors. This study provides key insights into the mechanisms underlying mucus degradation and underscores the value of human cell-derived mucus models for understanding bacteria-mucus interactions in health and disease.