Selective microbial electrosynthesis of methane by a pure culture of a marine lithoautotrophic archaeon

• A lithoautotrophic archaeon selectively produces methane at − 0.4 V vs. SHE.
• Methane production by strain IM1 proceeds with a coulomb efficiency of 80%.
• CO2 reduction by strain IM1 features a low overpotential of only − 0.16 V vs. SHE.
• Below − 0.4 V vs. SHE selectivity changes and H2 is evolved in a second pathway.
• Strain IM 1 shows great promise for bioelectrical conversion of renewable energy.

Reduction of carbon dioxide to methane by microorganisms attached to electrodes is a promising process in terms of renewable energy storage strategies. However the efficient and specific electrosynthesis of methane by methanogenic archaea on cathodes needs fundamental investigations of the electron transfer mechanisms at the microbe–electrode interface without the addition of artificial electron mediators. Using well-defined electrochemical techniques directly coupled to gas chromatography and surface analysis by scanning electron microscopy, it is shown that a pure culture of the marine lithoautotrophic Methanobacterium-like archaeon strain IM1 is capable to utilize electrons from graphite cathodes for a highly selective production of methane, without hydrogen serving as a cathode-generated electron carrier. Microbial electrosynthesis of methane with cultures of strain IM1 is achieved at a set potential of − 0.4 V vs. SHE and is characterized by a coulomb efficiency of 80%, with rates reaching 350 nmol d− 1 cm− 2 after 23 days of incubation. Moreover, potential step measurements reveal a biologically catalyzed hydrogen production at potentials more positive than abiotic hydrogen evolution on graphite, indicating that an excessive supply of electrons to strain IM1 results in proton reduction rather than in a further increase of methane production.

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