In vitro modulating gut microbiota by altering hydrogenotrophic activities
Hydrogen metabolism plays a central role in microbial fermentation. However, how hydrogenotrophic microbes impact microbiota composition and metabolites in gut ecosystems remains largely unknown. Hence, this study investigates the impact of altering two of the key hydrogenotrophic activities, namely methanogenesis and sulphate reduction, on human gut microbiota composition and metabolite production. Faecal slurries from three methane excretors (MEs) and three non-methane excretors (NMEs) were inoculated into basal medium with  1% (w/v) pectin or a carbohydrate mixture (pectin, potato starch , inulin, xylan and arabinogalactan; 0.2% each) as substrates. Methanogenesis was inhibited by adding 2-bromoethanesulfonate (BES)  was added to inhibit methane production in MEs, or stimulated by adding and Methanobrevibacter smithii was added to stimulate methane production in NMEs. Sodium sulphate was added to stimulate Ssulphate reduction was stimulated by adding sodium sulphate in both MEs and NMEs. Based on analysis of prokaryotic 16S rRNA gene amplicon sequence data and metabolites, Results in this study revealed that microbial richness and composition, propionate and methane production significantly differed between MEs and NMEs. Lower hydrogen concentrations were observed in MEs compared to NMEs in the incubations with pectin, but not  in the incubations with the carbohydrate mixture. Remarkably, sulphate was not consumed in either ME or NME incubations. Adding M. smithii to the NME inocula resulted in its persistence in the community and methane production during incubations. The addition of 2-bromoethanesulfonateBES inhibited methane production in the ME incubations, accompanied with a lower relative abundance of methanogens when pectin was used as substrate. However, altering methanogenesis did not significantly change overall microbiota composition and metabolite production in MEs and NMEs. These findings suggest that methanogens can occupy a niche in a microbiota that originally lacks methanogens, but that modulating methanogenesis has a minor effect on overall microbiota composition and activity.