Firmicute bacteria and the metabolites they produce are perturbed in ulcerative colitis (UC) patients. SER-287, an oral formulation of live Firmicute spores, was found to be safe and effective in achieving clinical remission in a Phase 1b clinical trial in mild-to-moderate UC. We assessed changes in the stool metabolome and host transcriptome among remitters and non-remitters as a measure of SER-287 pharmacodynamics.