Hydrogen Availability Is Dependent on the Actions of Both Hydrogen-Producing and Hydrogen-Consuming Microbes

Hydrogen gas (H 2 ) is produced by H 2 -producing microbes in the gut during polysaccharide fermentation. Gut microbiome also includes H 2 -consuming microbes utilizing H 2 for metabolism: methanogens producing methane, CH 4 , and sulfate-reducing bacteria producing hydrogen sulfide, H 2 S. H 2 S is not measured in the evaluation of gaseous byproducts of microbial fermentation. We hypothesize that the availability of measured H 2 depends on both hydrogen producers and hydrogen consumers by measuring H 2 in vitro and in vivo. In the in vitro study, groups were Bacteroides thetaiotaomicron ( B. theta , H 2 producers), Desulfovibrio vulgaris ( D. vulgaris , H 2 consumers), and D. vulgaris + B. theta combined. Gas samples were collected at 2 h and 24 h after incubation and assayed for H 2 , CH 4 , and H 2 S. In the in vivo study Sprague–Dawley rats were gavaged with suspended bacteria in four groups: B. theta , D. vulgaris , combined, and control. Gas was analyzed for H 2 at 60 min. In the in vitro experiment, H 2 concentration was higher in the combined group (188 ± 93.3 ppm) compared with D. vulgaris (27.17 ± 9.6 ppm) and B. theta groups (34.2 ± 29.8 ppm; P < 0.05); H 2 S concentration was statistically higher in the combined group (10.32 ± 1.5 ppm) compared with B. theta (0.19 ± 0.03 ppm) and D. vulgaris group (3.46 ± 0.28 ppm; P < 0.05). In the in vivo study, H 2 concentrations were significantly higher in the B. theta group (44.3 ± 6.0 ppm) compared with control (31.8 ± 4.3) and the combined group (34.2 ± 8.7, P < 0.05). This study shows that sulfate-reducing bacteria could convert available H 2 to H 2 S, leading to measured hydrogen levels that are dependent on the actions of both H 2 producers and H 2 consumers.