Fe0-dependent carbon dioxide reduction to methane via diverse electron transfer pathway in methanogenic community
Tianyu Gao, Lichao Xia, Hanmin Zhang, Ahmed Tawfik, Fangang Meng
Abstract
In natural and engineered environments, iron biocorrosion is an energy reservoir for growth of methanogens. However, how archaea accept electrons from metallic iron remains enigmatic. Here, we report that a Methanothrix-dominated methanogenic community from anaerobic granular sludge can reduce carbon dioxide (CO2) to methane (CH4) via electron uptake from zero-valent iron (ZVI). Through the batch experiments, a maximum CH4 yield of 40.8 ± 0.6 μeequiv/day and an electron recovery from ZVI oxidation to CH4 generation of 69.7% ± 6.1% are observed. Metagenome analysis and inhibition experiments indicate that electrons released by corrosive bacteria are utilized by Methanothrix for accomplishing CO2-to-CH4 conversion via potential intracellular and extracellular electron transfer. The results of activity tests of four electron donors (i.e., ZVI, stainless steel, H2, and acetate) suggest that the ZVI-dependent methanogenesis dominate the overall CH4 generation compared with hydrogenotrophic and acetoclastic methanogenesis, which provides a new insight into autotrophic metabolism of methanogens.