enhances HS production in .

Sulfate- and sulfite-reducing bacteria (SRB) are a group of strict anaerobes found within the human gut. , a sulfite-reducing bacterium which produces hydrogen sulfide (HS) from taurine and isethionate respiration, is a common member of the healthy commensal human gut microbiota but has been implicated in several disease states including inflammatory bowel disease and colorectal cancer. , one of the most prominent gut bacteria, has sulfatases which release sulfate, serving as a potential substrate for sulfate-reducing bacteria. Here, we showed that when and were in co-culture, there was a significant increase in 's growth and in HS production by . Differential gene expression analysis revealed increased expression of 's complex in co-culture, which delivers electrons for sulfite reduction to HS. This was accompanied by a decreased expression of genes associated with taurine, sulfolactate, and thiosulfate respiration, indicating that may provide an alternative source of sulfite to . We hypothesized adenosine 5'-phosphosulfate (APS) to be this intermediate. Indeed, was able to grow using APS or sulfite as electron acceptors. Endometabolomic and transcriptomic analyses revealed decreased production of indole by in co-culture with due to enhanced tryptophan utilization by . The results of this microbe-microbe interaction could have significant pro-inflammatory effects in the human gut environment.