Spatial heterogeneity determines the gastrointestinal microbiome signatures and ecological processes that govern bacterial community assembly in sheep

Sheep's gastrointestinal tract harbors a diverse microbial community crucial for immune system balance, nutrient digestion, and overall health. We explored the microbial community composition, community types (enterotypes), bacterial interactions, and ecological processes in 10 gastrointestinal regions of 36 six-month-old Hu sheep raised under same diets and environmental conditions. Our findings revealed a unique U-shaped pattern of bacterial diversity from the rumen to the rectum, with the lowest diversity in the jejunum. The composition and enterotypes of bacterial communities varied spatially along the gastrointestinal tract, primarily categorized into three distinct groups. The rumen exhibited the highest abundance of bacterial taxa, unique taxa, and unique functions, while the enterotypes in the three regions of the large intestine were consistent. We explored the assembly processes of bacterial communities, elucidating how they find their ecological niches based on their characteristics and environmental demands. The assembly processes in the four-chambered stomach and small intestine resembled random selection, where bacterial positioning depended on luck and chance, while in the large intestine, it appeared more deterministic, with specific bacteria likely selected based on their unique skills and environmental requirements. This study enhances our understanding of microbial coexistence and interactions in complex ecosystems, with implications for improving animal productivity, disease treatment, and the development of novel microbial formulations.