Oxygen gradients shape cross-feeding, leading to emergent spatial organization in gut commensal bacteria

B. thetaiotaomicron colonizes anoxic regions where it degrades polysaccharides, while E. coli occupies oxygenated zones where it consumes the released sugars. Through aerobic respiration, E. coli locally reduces oxygen, widening the anoxic region that B. thetaiotaomicron subsequently invades. Disrupting sugar uptake in E. coli collapses this organization, whereas increasing oxygen availability reverses it.

A reaction–transport model shows that these patterns arise from coupled feedbacks between resource release, resource consumption, and oxygen modification. Together, our results reveal how spatial structure and physicochemical gradients convert a cross-feeding interaction into a dynamic niche-construction process that stabilizes coexistence and generates emergent ecological organization.