抄録
In deep aquifers associated with accretionary prisms, significant methane (CH4) is produced by a subterranean microbial community that includes methanogenic archaea and anaerobic bacteria. Here, we developed a microbial methanation system for producing CH4 from molecular hydrogen (H2) and carbon dioxide (CO2) using a subterranean microbial community derived from a deep aquifer. An isolated strain belonging to hydrogenotrophic methanogens was also used as a control. The microbial community and the strain were added to liquid culture media, respectively. Then, the cultures were amended with H2/CO2 gas, and anaerobically incubated in serum bottles. The results showed that continuous and stable CH4 production occurred in both cultures. In order to evaluate the effect of molecular oxygen (O2) mixed into the cultures, we also attempted culture experiments in which air was artificially added to serum bottles along with H2/CO2. The results showed that addition of air to the culture using the strain of hydrogenotrophic methanogens inhibited CH4 production. On the other hand, in the cultures using the subterranean microbial community containing hydrogenotrophic methanogens, CH4 production was observed even when 5% air was added. These results suggest that bacteria in a subterranean microbial community, e.g., facultative anaerobic bacteria, efficiently consume O2 and play a role in maintaining an anaerobic condition in the culture system. Further, the reducing agent (Na2S・9H2O) reduces O2 in the cultures, and SO42− is generated. Then, it is possible that the sulfate-reducing bacteria included in the subterranean microbial community reduce the SO42− and thereby regenerate the reducing agent. Our study demonstrates the effectiveness of a subterranean microbial community containing a bacterial community, as well as hydrogenotrophic methanogens, in constructing a microbial methanation system.