Intestinal mucus promotes microbial degradation of bamboo fiber in an in vitro giant panda gut fermentation system

In some hindgut-fermenting animals, the intestine secretes mucus that provides physical lubrication and protection under high-fiber dietary conditions, yet the role of this mucus in plant-fiber degradation by the gut microbiota remains unclear. The unique "mucus expulsion" of giant pandas offers an ideal model to investigate the physiological significance of mucus in herbivore dietary adaptation.

We established an in-vitro gut-mimicking system with mucus as the key variable. We quantified bamboo fiber degradation, visualized microstructural damage via scanning electron microscopy (SEM), and analyzed the microbial community and functional potential using 16S rRNA sequencing. Null model-based ecological process inferences (NST, βNTI) were employed to probe community assembly mechanisms.

In the mucus system, the degradation of bamboo cellulose and hemicellulose was significantly enhanced (P < 0.05), with scanning electron microscopy (SEM) revealing extensive damage to bamboo fiber tissues. This enhanced degradation was associated with the predicted microbial functions related to plant polysaccharide metabolism, including diverse hydrolases (e.g. GH2/3/43) and transport systems. The primary contributors to this genetic potential were enriched fiber-hydrolyzing genera, including Bacteroides and Dysgonomonas, which actively interacted with resident probiotics and other commensal bacteria. Community assembly analysis suggested that the mucus physicochemical environment imposed deterministic constraints on microbial community composition, while phylogenetic turnover remained within stochastic expectations and was primarily characterized by dispersal limitation.

Within the mucus physicochemical environment, a specifically assembled microbial consortium was associated with enhanced bamboo fiber degradation and nutrient acquisition. These findings provide new insights into the potential role of mucus in supporting microbial adaptation to a bamboo-based diet in giant pandas.