Aerobic H2respiration enhances metabolic flexibility of methanotrophic bacteria

Methanotrophic bacteria are important soil biofilters for the climate-active gas methane. The prevailing opinion is that these bacteria exclusively metabolise single-carbon, and in limited instances, short-chain hydrocarbons for growth. This specialist lifestyle juxtaposes metabolic flexibility, a key strategy for environmental adaptation of microorganisms. Here we show that a methanotrophic bacterium from the phylum Verrucomicrobia oxidises hydrogen gas (H 2 ) during growth and persistence. Methylacidiphilum sp. RTK17.1 expresses a membrane-bound hydrogenase to aerobically respire molecular H 2 at environmentally significant concentrations. While H 2 oxidation did not support growth as the sole electron source, it significantly enhanced mixotrophic growth yields under both oxygen-replete and oxygen-limiting conditions and was sustained in non-growing cultures starved for methane. We propose that H 2 is consumed by this bacterium for mixotrophic growth and persistence in a manner similar to other non-methanotrophic soil microorganisms. We have identified genes encoding oxygen-tolerant uptake hydrogenases in all publicly-available methanotroph genomes, suggesting that H 2 oxidation serves a general strategy for methanotrophs to remain energised in chemically-limited environments.