Secondary Bile Acids Modified by <i>Odoribacter Splanchnicus</i> Alleviate Colitis by Suppressing Neutrophil Extracellular Trap Formation

The gut microbiota contributes to inflammatory bowel disease (IBD) pathogenesis, yet the functional impact of specific bacterial species remains unclear. Here, Odoribacter splanchnicus (O. splanchnicus) is indentified as a taxon depleted in human IBD cohorts and demonstrated its protective effects in acute and chronic murine colitis models. In mice, O. splanchnicus administration alleviated colonic inflammation and preserved barrier integrity, accompanied by a restructured mucosal immune landscape and reduced neutrophil extracellular traps (NETs) formation. This inhibitory effect on NETs is lost in Pad4^-/- mice, highlighting its dependence on NETs formation machinery. Metabolomic profiling showed that O. splanchnicus treatment elevated the secondary bile acid lithocholic acid (LCA). This increase is lost following antibiotic cocktail treatment and restored by fecal microbiota transplantation from O. splanchnicus-treated donors, demonstrating a requirement for an intact gut microbiota. Mechanistically, LCA supplementation recapitulated the anti-NETs formation phenotype and suppressed colonic inflamation by inhibiting the NLRP3-GSDMD signaling pathway. Together, these findings define a gut microbiota-metabolite-neutrophil axis in IBD pathogenesis, highlighting the microbiota-dependent regulation of LCA as a key protective mechanism of O. splanchnicus.