Contribution of Common Sulfur-Containing Substrates to Hydrogen Sulfide Production By Human Gut Microbiota Using an In Vitro Model Standardized For Bacterial Counts

Hydrogen sulfide (H2S) produced by human gut microbiota is highly toxic and implicated in pathogenesis of gastrointestinal tract disorders. Sulfur-containing amino acid (SAA) degradation is a major contributor to its production, but SAA degradation pathways have not been extensively characterized. In vitro model systems of fecal H2S production offer a basic method to help elucidate SAA degradation pathways, but the approach is not standardized. To address this, we used fecal microbiota separated from feces and standardized for bacterial counts to measure H2S production potential in response to different substrates in healthy controls (n = 6) with repeated sampling (three samples per participant). H2S production was highest with cysteine (mean = 16.7 ppm) compared to sodium sulfate (0.7 ppm) and taurine (0.8 ppm). Sodium-sulfate-driven H2S production negatively correlated with Ruminococcus (Spearman’s ρ = −0.5) and cysteine-driven H2S production negatively correlated with Firmicutes (Spearman’s ρ = −0.5). These findings, using a protocol controlling for confounding variables such as bacterial counts, validate previous findings of cysteine as a primary driver of H2S production. Finally, the inclusion of samples from two patients with UC allowed for the illustration of the potential of this approach to identify functional differences in specific disease states.