Capsular polysaccharide correlates with immune response to the human gut microbe Ruminococcus gnavus

Significance Microbes shape human health and disease. Today, there are increasing correlations of gut microbes with specific diseases, but the underlying molecules and mechanism linking the two are not known. This stifles both the understanding of disease causation and the development of suitable treatments. We investigated a dozen patient isolates of Ruminococcus gnavus , a prevalent gut microbe linked to inflammatory bowel disease (IBD). We found that some isolates possess a protective capsule that encourages a symbiotic relationship with the host immune system, while others lack this protective capsule and elicit a robust inflammatory immune response. This work reveals a path by which R. gnavus could be connected to IBD and potential therapeutic interventions.