Methanosarcina barkeri-D8 Raw sequence reads
Application of current can stimulate biomass removal and methane production in anaerobic digesters where Methanosarcina are frequently found. Therefore, the impact of current on methanogenesis by M. barkeri was examined. Cells were grown in reactors with methanol and cathodes poised at different potentials (-0.6 V and -1.0 V vs. Ag/AgCl). CH4/CO2 ratios (4.9:1 and 5.6:1) and CO2 conversion efficiencies (24% and 43%) for the -0.6V and -1.0V reactors were higher than the non-current control reactor (3.46:1 and 7%). Cathodic H2 provided an additional source of electrons in the -1.0V reactor, however, no electron mediators were detected in the -0.6V reactor. Cells were tightly attached to the -0.6V cathode, suggesting that M. barkeri obtained additional electrons directly from the -0.6V cathode. Transcriptomics revealed that genes for methylotrophic methanogenesis, CO2 reduction, carbon fixation, and intracellular hydrogen cycling were more highly expressed in current-exposed cells than the non-current control. In particular, transcripts for Vht and Frh hydrogenase genes were > 3.4 times more abundant in cells grown with poised cathodes. These results show that M. barkeri uses similar pathways for electron uptake in the presence of current, whether electrons are being acquired directly from the cathode surface or indirectly from cathodic H2.