<i>Bacteroides thetaiotaomicron</i> enhances H ₂ S production in <i>Bilophila wadsworthia</i>

Sulfate- and sulfite-reducing bacteria (SRB) are a group of strict anaerobes found within the human gut. <i>Bilophila wadsworthia</i>, a sulfite-reducing bacterium which produces hydrogen sulfide (H₂S) 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. <i>Bacteroides thetaiotaomicron</i>, 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 <i>B. thetaiotaomicron</i> and <i>B. wadsworthia</i> were in co-culture, there was a significant increase in <i>B. thetaiotaomicron</i>'s growth and in H₂S production by <i>B. wadsworthia</i>. Differential gene expression analysis revealed increased expression of <i>B. wadsworthia</i>'s <i>dsrMKJOP</i> complex in co-culture, which delivers electrons for sulfite reduction to H₂S. This was accompanied by a decreased expression of genes associated with taurine, sulfolactate, and thiosulfate respiration, indicating that <i>B. thetaiotaomicron</i> may provide an alternative source of sulfite to <i>B. wadsworthia</i>. We hypothesized adenosine 5'-phosphosulfate (APS) to be this intermediate. Indeed, <i>B. wadsworthia</i> was able to grow using APS or sulfite as electron acceptors. Endometabolomic and transcriptomic analyses revealed decreased production of indole by <i>B. thetaiotaomicron</i> in co-culture with <i>B. wadsworthia</i> due to enhanced tryptophan utilization by <i>B. wadsworthia</i>. The results of this microbe-microbe interaction could have significant pro-inflammatory effects in the human gut environment.