海岸带生物学与生物资源保护实验室知识库

[Xiao, Leilei

Methane is a major greenhouse gas responsible of global warming and renewable energy, but the precise contribution of biomethane from microbial decomposition is vague because microbial mechanisms are not fully understood. CO2 reduction and direct acetate dismutation are two main pathways for biomethane production, accounting for similar to 1/3 and 2/3 of produced methane in terrestrial ecosystems, respectively. A classical process explaining methane production involves CO2 reduction by direct interspecies electron transfer (DIET). Herein, we hypothesized that methane could also be produced by direct acetate dismutation by syntrophy between electron-donating Shewanella oneidensis MR-1 and electron-accepting methanogens. We tested the effect of two conducing carbon materials, granular activated carbon and carbon nanotubes, on methane production. The electrical activity was monitored with a microbial fuel cell. We used CH3F, C-13 labelling, thermodynamics, DNA analysis and modelling to elucidate the mechanism. Results show that the rate of methane production increased by 29.0% using S. oneidensis MR-1, and by 36.2-40.7% using S. oneidensis MR-1 and conducing materials. C-13 labelling shows that about 94% of methane is produced by acetate dismutation. Findings further show that acetate dismutation is enhanced by exoelectrogenic activity, thus suggesting that electrons from S. oneidensis MR-1 are used to convert methyl groups into methane. Overall our results disclose DIET-acetate dismutation as an alternative mechanism of biomethane production, which is highly stimulated by carbon-based conducive materials. These findings are of significance for further understanding methanogenic progresses with the involvement of electroactive microorganisms in natural environments and artificial anaerobic systems.