GVHD patients have reduced diversity, abundance of butyrate producers, and loss of anaerobiosis pre- and post-GVHD onset. (A) Pre- and postonset aGVHD microbial analysis show reduced diversity in GI GVHD patients. (B) GI GVHD patients also had lower relative abundance of predicted butyrate-producing strains when compared with the other cohorts, and this was also found for LGI patients when compared with non-GI and UGI patients postonset. (C) GVHD patients also had lower strict-to-facultative (S/F) anaerobe ratio in comparison with no-GVHD patients, whereas the LGI patients, specifically, showed lower ratio when compared with UGI and non-GI patients, respectively pre- and postonset.