Anaerobic dihydrogen consumption of nutrient-limited aquifer sediment microbial communities examined by stable isotope analysis.

The biogeochemical consequences of dihydrogen (H₂) underground storage in porous aquifers are poorly understood. Here, the effects of nutrient limitations on anaerobic H₂ oxidation of an aquifer microbial community in sediment microcosms were determined in order to evaluate possible responses to high H₂ partial pressures. Hydrogen isotope analyses of H₂ yielded isotope depletion in all biotic setups indicating microbial H₂ consumption. Carbon isotope analyses of carbon dioxide (CO₂) showed isotope enrichment in all H₂-supplemented biotic setups indicating H₂-dependent consumption of CO₂ by methanogens or homoacetogens. Homoacetogenesis was indicated by the detection of acetate and formate. Consumption of CO₂ and H₂ varied along the differently nutrient-amended setups, as did the onset of methane production. Plotting carbon against hydrogen isotope signatures of CH₄ indicated that CH₄ was produced hydrogenotrophically and fermentatively. The putative hydrogenotrophic Methanobacterium sp. was the dominant methanogen. Most abundant phylotypes belonged to typical ferric iron reducers, indicating that besides CO₂, Fe(III) was an important electron acceptor. In summary, our study provides evidence for the adaptability of subsurface microbial communities under different nutrient-deficient conditions to elevated H₂ partial pressures.