Role of Vht hydrogenase in electron uptake by Methanosarcina barkeri from a cathode

Electrical currents can enhance biomass removal and methane production in anaerobic digesters, particularly where Methanosarcina species like Methanosarcina barkeri are active. To explore how M. barkeri acquires electrons from cathodes, M. barkeri was inoculated into methanol-fed reactors with applied cathodic potentials that either generated hydrogen (−1.0 V vs. Ag/AgCl) or did not (−0.6 V). Transcriptomic analysis revealed increased expression of genes tied to carbon metabolism and intracellular hydrogen cycling in −0.6 V cells. Transcripts for Vht and Frh hydrogenase genes were also more abundant in −0.6 V cells, and flux balance analysis confirmed Vht hydrogenases' importance in electron uptake. A mutant lacking vhtGAC genes showed delayed growth in reactors with −0.6 V cathodes but compensated by upregulating Fpo dehydrogenase genes. These findings shed light on how M. barkeri facilitates direct electron uptake (direct electron transfer [DET]) from cathodes and should help improve methane production in bioelectrochemical systems.