To determine the causes of the reduced susceptibility of Ido1 deficient mice to DSS-induced colitis, we tested the hypothesis that differential composition of the gut microbiota between Ido1 deficient and wildtype mice might affect disease progression. Wildtype and Ido1 deficient mice were administered DSS in the drinking water ad libitum for 7 days. Following the development of acute colitis, colonic contents were collected from each mouse for 16S ribosomal RNA (16S rRNA) gene-targeted analysis.