Deciphering the in vitro mucin-driven interaction dynamics of a synthetic gut bacterial community

The gut microbiota is a complex microbial community that plays a crucial role in host health. Environmental and biological factors within the ecosystem influence the dynamic interactions among its members. Although dietary and host-derived nutrient availability play a key role in shaping microbial ecology and interaction patterns, the dynamics of these interactions within the mucus layer remain poorly understood. In this study, we analyzed a synthetic community comprised of six species with variable abilities to utilize mucin. We performed in vitro growth analyses and monitored the interactions among community members in monoculture, co-culture, and community batch culture under different nutrient conditions. Our results showed that positive interactions were prevalent among bacteria when mucin served as the sole carbon source. In contrast, the addition of glucose or high nutrient availability significantly increased inter-bacterial competition. These findings suggest that mucin mitigates competitive antagonism and potentially promotes community diversity. Further in vivo studies supported the role of mucin in increasing community diversity and modulating bacterial metabolic patterns. Deciphering these intricate relationships is essential for understanding how gut microbiota stability is maintained, and what factors might disrupt this delicate balance.IMPORTANCEThe gut microbiota is essential for host health, yet microbial interactions within the intestinal mucus layer remain poorly understood. Current understanding of gut microbial ecology is largely based on nutrient-rich media that do not accurately reflect the mucosal environment. Here, we demonstrate that when bacteria rely solely on mucin as a carbon source, cooperative interactions predominate. In contrast, the introduction of simple sugars shifts the balance toward intensified interbacterial competition. Mucin mitigates competitive antagonism, promotes resource utilization, and enhances community diversity. By demonstrating that mucus actively shapes microbial interaction patterns, this study provides a mechanistic framework for understanding gut ecosystem resilience. Furthermore, these findings support the development of more physiologically relevant in vitro models for predicting gut microbial dynamics and may guide microbiome-based therapies.