Bacterial groups that were ubiquitously present in the mucosa of the five individuals.

Ubiquity was defined based on the presence of related OTUs in (i) >90% of the 30 biopsy samples, and (ii) were present in at least one of biopsy duplicates retrieved at a particular colonic site of the individual. The OTUs were blasted for their phylogenetic affiliations on RDP. The consensus model OTU sequences can be found in Material S1.