Abstract
The biomethane formation from 4 H2 + CO2 by pure cultures of two methanogens, Methanocaldococcus fervens and Methanobacterium thermophilum, has been studied. The goal of the study was to understand the regulation of the enzymatic steps associated with biomethane biosynthesis by H2, using metagenomic, pan-genomic, and transcriptomic approaches. Methanogenesis in the autotrophic methanogen M. fervens could be easily "switched off" and "switched on" by H2/CO2 within about an hour. In contrast, the heterotrophic methanogen M. thermophilum was practically insensitive to the addition of the H2/CO2 trigger although this methanogen also converted H2/CO2 to CH4. From practical points of view, the regulatory function of H2/CO2 suggests that in the power-to-gas (P2G) renewable excess electricity conversion and storage systems, the composition of the biomethane-generating methanogenic community is essential for sustainable operation. In addition to managing the specific hydrogenotrophic methanogenesis biochemistry, H2/CO2 affected several, apparently unrelated, metabolic pathways. The redox-regulated overall biochemistry and symbiotic relationships in the methanogenic communities should be explored in order to make the P2G technology more efficient. KEY POINTS : • Hydrogenotrophic methanogens may respond distinctly to H2/CO2 in bio-CH4 formation. • H2/CO2 can also activate metabolic routes, which are apparently unrelated to methanogenesis. • Sustainable conversion of the fluctuating renewable electricity to bio-CH4 is an option.