Regulation of the methanogenesis pathways by hydrogen at transcriptomic level in time

The biomethane formation from 4 H 2 + CO 2 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 H 2 , using metagenomic, pan-genomic, and transcriptomic approaches. Methanogenesis in the autotrophic methanogen M. fervens could be easily “switched off” and “switched on” by H 2 /CO 2 within about an hour. In contrast, the heterotrophic methanogen M. thermophilum was practically insensitive to the addition of the H 2 /CO 2 trigger although this methanogen also converted H 2 /CO 2 to CH 4 . From practical points of view, the regulatory function of H 2 /CO 2 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, H 2 /CO 2 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 H 2 /CO 2 in bio-CH 4 formation. • H 2 /CO 2 can also activate metabolic routes, which are apparently unrelated to methanogenesis. • Sustainable conversion of the fluctuating renewable electricity to bio-CH 4 is an option.