 This study identifies facultative anaerobes and ruminococcus navus as significantly abundant in inflammatory bowel disease, IBD, patients, with a distinct clade of unnavis enriched in IBD patients. The study also identifies 199 IBD-specific, strain-specific genes involved in oxidative stress responses, adhesion, ion acquisition, and mucus utilization in this unnavis clade, potentially conferring an adaptive advantage for this strain in the IBD gut. This article was authored by Andrew Brantley Hall, Moran Yasa, Jenny Sork, and others.