Biological methane production coupled with sulfur oxidation in a microbial electrosynthesis system without organic substrates

Akiyoshi Ohashi , Ha T.T. Dinh , Hiromi Kambara , Shuji Matsushita , Yoshiteru Aoi , Tomonori Kindaichi , Noriatsu Ozaki


Received May 05, 2021,Revised , Accepted July 27, 2021, Available online January 11, 2022

Volume 34,2022,Pages 68-78

Methane is produced in a microbial electrosynthesis system (MES) without organic substrates. However, a relatively high applied voltage is required for the bioelectrical reactions. In this study, we demonstrated that electrotrophic methane production at the biocathode was achieved even at a very low voltage of 0.1 V in an MES, in which abiotic HS oxidized to SO42− at the anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H2 was produced by syntrophic bacteria, such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea, and Aminicenantales, with the direct acceptance of electrons at the biocathode. Subsequently, most of the produced H2 was converted to acetate by homoacetogens, such as Clostridium and Spirochaeta 2. In conclusion, the majority of the methane was indirectly produced by a large population of acetoclastic methanogens, namely Methanosaeta, via acetate. Further, hydrogenotrophic methanogens, including Methanobacterium and Methanolinea, produced methane via H2.

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