TLR4—a host gene known to modulate inflammatory response in intestinal epithelium through recognition of bacterial lipopolysaccharide95, and previously implicated in IBD and CRC96,97—is found to be associated with an oral microbe GN02 in CRC98, whereas in IBD it associates with Acidaminococcaceae—a gut microbe found to be increased in abundance in patients with Crohn’s disease99 (Fig. 4b, Network 4). Here, TLR4 is linked to irritable bowel syndrome.