Metatranscriptomic-driven insights into mucosal glycan degradation by the human gut microbiota

The secreted mucus layer in the human gastrointestinal tract constitutes both a protective boundary between gut lumen and epithelium as well as an important nutrient source for members of the gut microbiota. While many gut microbes possess the genetic potential to degrade mucin, it is still unclear which species transcribe the respective genes. Here, we systematically analysed publicly available metagenome and metatranscriptome datasets to characterize the gut microbial community involved in mucosal glycan degradation. We utilized cooccurrence network analysis and linear regression to elucidate the ecological strategies of, and relationship between, mucus degraders. We found that although ~60% of species carrying genes encoding for mucosal-glycan-degrading enzymes have detectable transcription of these genes, only 21 species prevalently transcribe more than 1 gene. Furthermore, the transcription of individual genes was frequently dominated by single species in individual samples. Transcription patterns suggested the presence of competitive mucosal glycan degraders characterized by abundance-driven transcription that were negative predictors for the transcription of other degraders as well as opportunistic species with decoupled abundance and transcription profiles. These findings provide insights into the ecology of the mucosal glycan degradation niche in the human gut microbiota.