The second largest sink for atmospheric methane (CH4) is atmospheric methane oxidizing-bacteria (atmMOB). How atmMOB are able to sustain life on the low CH4 concentrations in air is unknown. Here, we show that during growth, with air as its only source for energy and carbon, the recently isolated atmospheric methane-oxidizer Methylocapsa gorgona MG08 (USCα) oxidizes three atmospheric energy sources: CH4, carbon monoxide (CO), and hydrogen (H2) to support growth. The cell-specific CH4 oxidation rate of M. gorgona MG08 was estimated at ~0.7 × 10-18 mol cell-1 h-1, which, together with the oxidation of CO and H2, supplies 0.38 kJ Cmol-1 h-1 during growth in air. This is seven times lower than previously assumed necessary to support bacterial maintenance. We conclude that atmospheric methane-oxidation is supported by a metabolic flexibility that enables the simultaneous harvest of CH4, H2 and CO from air, but the key characteristic of atmospheric CH4 oxidizing bacteria might be very low energy requirements.
Keywords: atmospheric trace gases; carbon monoxide; energy; growth; hydrogen; methane.