R. gnavus is a mucin-degrading bacteria, which has been associated with inflammatory bowel disease, produces secondary bile acids, which can affect overall community composition in the gut, and produces an inflammatory polysaccharide.52,53 We found an enrichment in the metabolic process for mucus degradation in ME/CFS from functional metagenomic analyses. Here, MUC5AC is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.