Eubacterium rectale contributes to colorectal cancer initiation via promoting colitis.

Inflammatory bowel disease caused by microbial dysbiosis is an important factor contributing to colorectal cancer (CRC) initiation. The 'driver-passenger' model in human gut microbial dysbiosis suggests that 'driver' bacteria may colonize with low relative abundance on tumor site but persistently induce chronic change in normal intestinal epithelium and initiate CRC. They are gradually replaced by 'passenger' bacteria later on, due to their low adaptability to the on-tumor site niche. To reveal site-specific bacterial taxon markers in CRC patients, we analyzed the gut mucosal microbiome of 75 paired samples of on-tumor and tumor-adjacent sites, 75 off-tumor sites, and 26 healthy controls. Linear discriminant analysis of relative abundance profiles revealed unique bacterial taxon distribution correlated with specific tumor sites, with Eubacterium having the distribution characteristic of potential driver bacteria. We further show that Eubacterium rectale endotoxin activates the transcription factor NF-κΒ, which regulates multiple aspects of innate and adaptive immune responses in normal colon epithelial cells. Unlike the 'passenger' bacterium Fusobacterium nucleatum, E. rectale promotes dextran sodium sulfate-induced colitis in Balb/c mice. Our findings reveal that E. rectale functions as a 'driver' bacterium and contributes to cancer initiation via promoting inflammation.