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

Hydrogen gas (H) is produced by H-producing microbes in the gut during polysaccharide fermentation. Gut microbiome also includes H-consuming microbes utilizing H for metabolism: methanogens producing methane, CH, and sulfate-reducing bacteria producing hydrogen sulfide, HS. HS is not measured in the evaluation of gaseous byproducts of microbial fermentation. We hypothesize that the availability of measured H depends on both hydrogen producers and hydrogen consumers by measuring H in vitro and in vivo. In the in vitro study, groups were Bacteroides thetaiotaomicron (B. theta, H producers), Desulfovibrio vulgaris (D. vulgaris, H consumers), and D. vulgaris + B. theta combined. Gas samples were collected at 2 h and 24 h after incubation and assayed for H, CH, and HS. 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 at 60 min. In the in vitro experiment, H 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); HS 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 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 to HS, leading to measured hydrogen levels that are dependent on the actions of both H producers and H consumers.