| Summary: | The second largest sink for atmospheric methane (CH<sub>4</sub>) is atmospheric methane oxidizing-bacteria (atmMOB). How atmMOB are able to sustain life on the low CH<sub>4</sub> 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 <i>Methylocapsa gorgona</i> MG08 (USCα) oxidizes three atmospheric energy sources: CH<sub>4</sub>, carbon monoxide (CO), and hydrogen (H<sub>2</sub>) to support growth. The cell-specific CH<sub>4</sub> oxidation rate of <i>M. gorgona</i> MG08 was estimated at ~0.7 × 10<sup>−18</sup> mol cell<sup>−1</sup> h<sup>−1</sup>, which, together with the oxidation of CO and H<sub>2</sub>, supplies 0.38 kJ Cmol<sup>−1</sup> h<sup>−1</sup> 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 CH<sub>4</sub>, H<sub>2</sub> and CO from air, but the key characteristic of atmospheric CH<sub>4</sub> oxidizing bacteria might be very low energy requirements.
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