Microbial resource management for ex situ biomethanation of hydrogen at alkaline pH

Biomethanation is a promising solution to convert H2 produced by surplus electricity and CO2 to methane by exploiting the metabolic potential of hydrogenotrophic methanogens. In ex situ biomethanation with mixed cultures, homoacetogens and methanogens compete for H2/CO2. We enriched a hydrogenotrophic microbiota to investigate these competing reactions at alkaline pH and applied the concept of microbial resource management. Microbial community structure and dynamics of bacteria and methanogenic archaea were evaluated through 16S rRNA and mcrA amplicon sequencing, respectively. Hydrogenotrophic methanogens and homoacetogens were enriched as acetate was concomitantly produced with CH4. The predominating methanogens belonged to the genera Methanobacterium and Methanoculleus. The bacterial community was dominated by Lutispora. The methanogenic community was stable, whereas the bacterial community was more dynamic. Our results suggest that microbial resource management for ex situ biomethanation can be achieved by adapting the media composition, the reducing agent and the stirring intensity to selectively produce CH4 from H2/CO2.