Identification of the biomethanation pathways during biological CO2 fixation with exogenous H2 addition

Power-to-gas allows conversion of surplus electricity to methane when CO 2 is available, which becomes an important technology for carbon capture, utilization and sequestration, as well as for increasing the flexibility of electricity production from renewable energy resources such as wind and solar energy. H 2 /CO 2 biomethanation is a potentially promising alternative to the conversion of H 2 /CO 2 to methane without limitation of variable hydrogen production. To identify mixed culture-based metabolic pathways of H 2 /CO 2 under the mesophilic (35 °C) and thermophilic (55 °C) conditions, two specific inhibitors, 2-bromoethane sulfonate (BES) and vancomycin were employed in this experimental study. The combination of hydrogenotrophic and homoacetogenesis-acetoclastic methanogenesis makes up the pathway for the mesophilic cultivated microbial consortia. 16S rRNA gene analysis indicates that abundant Bacteria , Methanobacterium and Methanosaeta play important role in the conversion. Further analysis shows close collaboration between microorganisms by the formation of microbial clustering and the production of humic acids. The detailed metabolic mechanisms further confirm a diverse biomethanation network under the mesophilic condition. While under the thermophilic condition, the H 2 /CO 2 biomethanation is fully dominated by the direct hydrogenotrophic methanogenesis mainly with Methanothermobacter , which is straightforward but more efficient. • H 2 /CO 2 biomethanation network is diversified at 35 °C. • H 2 /CO 2 biomethanation is dominated by hydrogenotrophic methanogenesis at 55 °C. • Temperature changes the species and spatial distribution of Bacteria and Archaea . • The differences of the interspecific collaboration change biomethanation pathways.