Abstract
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.
Highlights
The second largest sink for atmospheric methane (CH4 ) is atmospheric methane oxidizingbacteria
While the size of M. gorgona MG08 cells do not change when growing with air as its energy and carbon source, compared to higher CH4 concentrations, we acknowledge section above
While the size of M. gorgona MG08 cells do not change when growing with air as its energy and carbon source, compared to higher CH4 concentrations, we acknowledge thatthe thecontent, content,density densityand andthus thusdry dryweight weightofofthe thecells cellsgrowing growingininairairmay maydiffer differfrom from that thatofofM.M.gorgona gorgona
Summary
From the atmosphere annually [1]. The most common hypothesis for explaining how these bacteria can sustain life by oxidizing atmospheric CH4 is the “high affinity” model, in which a special form of particulate CH4 monooxygenase allows atmMOB to oxidize the low atmospheric CH4 concentrations at a high rate [2]. AtmMOB were expected to either utilize alternative energy sources or have high affinities for CH4 [3]. The recently described USCα atmMOB species Methylocapsa gorgona MG08 has the highest specific affinity (Vmax(app) /Km(app) ) for CH4 of all tested MOB at 195 × 10−12 L·cell−1 ·h−1. This translates into a cell-specific CH4 oxidation rate of only 10 × 10−18 mol CH4 cell−1 h−1 at atmospheric CH4 concentration [4], seemingly too low to support cellular maintenance [6]. We have studied how the atmospheric CH4 oxidizer M. gorgona MG08, in pure culture, harvests energy from the atmosphere for growth
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