Light-driven carbon dioxide reduction to methane by Methanosarcina barkeri-CdS biohybrid

Semi-artificial photosynthesis has emerged as a promising approach to convert carbon dioxide to value-added chemicals. Herein, direct CO2-to-CH4 conversion was realized by an innovative biohybrid consisting of semiconductor nanoparticles and non-phototrophic methanogens. The interaction between a model methanogen Methanosarcina barkeri and photoactive CdS nanoparticles achieved a CH4 production rate of 0.19 μmol/h with a quantum efficiency of 0.34%, comparable to that of plants or algae. The M. barkeri-CdS biohybrid exhibited a higher electrical conductivity than M. barkeri only and generated photocurrent in response to irradiation. The simultaneous increase of mcrA gene copies by 151.4% illustrated the robustness of this M. barkeri-CdS biohybrid. Membrane-bound proteins were found to play a key role in the photoelectron transfer. The CO2-to-CH4 conversion was possibly conducted with photoelectrons from the e−-h+ separation via the H2ases-mediated and cytochromes-mediated pathways. The findings encourage further exploration of the solar-driven self-replicating biocatalytic system to achieve CO2-to-CH4 conversion.