Early response of methanogenic archaea to H2 as evaluated by metagenomics and metatranscriptomics

The early response of the mixed mesophilic microbial community to H2 gas injection was investigated with the goal of uncovering the first responses of the microbial community in the CH4 formation and CO2 mitigation Power to Gas process. The overall microbial composition changes following a 10 min H2 injection by excessive bubbling H2 through the reactor was investigated via whole-genome DNA sequencing and transcriptome analysis of the rRNA depleted mRNA population via cDNA sequencing. Two hours after the H2 treatment the overall composition and taxonomic abundance did not change appreciably indicating that this time period was too short to display differences in the proliferation of the members of the microbial community. There was, however, a substantial increase in the expression of genes related to hydrogenotrophic methanogenesis of certain groups of Archaea. Surprisingly, H2 injection also altered the metabolism of a number of microbes belonging to the kingdom Bacteria. The importance of syntrophic cross-kingdom interactions in H2 metabolism and the related effects on the related Power-to-Gas process are discussed. Mixed communities are recommended for the large scale Power-to-Gas process rather than single hydrogenotrophic methanogen strains.