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

The biogeochemical consequences of dihydrogen (H-2) underground storage in porous aquifers are poorly understood. Here, the effects of nutrient limitations on anaerobic H(2 )oxidation of an aquifer microbial community in sediment microcosms were determined in order to evaluate possible responses to high H-2 partial pressures. Hydrogen isotope analyses of H-2 yielded isotope depletion in all biotic setups indicating microbial H-2 consumption. Carbon isotope analyses of carbon dioxide (CO2) showed isotope enrichment in all H-2-supplemented biotic setups indicating H-2-dependent consumption of CO2 by methanogens or homoacetogens. Homoacetogenesis was indicated by the detection of acetate and formate. Consumption of CO2 and H-2 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 H-2 partial pressures.