Widespread soil bacterium that oxidizes atmospheric methane

<jats:p> The global atmospheric level of methane (CH <jats:sub>4</jats:sub> ), the second most important greenhouse gas, is currently increasing by ∼10 million tons per year. Microbial oxidation in unsaturated soils is the only known biological process that removes CH <jats:sub>4</jats:sub> from the atmosphere, but so far, bacteria that can grow on atmospheric CH <jats:sub>4</jats:sub> have eluded all cultivation efforts. In this study, we have isolated a pure culture of a bacterium, strain MG08 that grows on air at atmospheric concentrations of CH <jats:sub>4</jats:sub> [1.86 parts per million volume (p.p.m.v.)]. This organism, named <jats:italic>Methylocapsa gorgona</jats:italic> , is globally distributed in soils and closely related to uncultured members of the upland soil cluster α. CH <jats:sub>4</jats:sub> oxidation experiments and <jats:sup>13</jats:sup> C-single cell isotope analyses demonstrated that it oxidizes atmospheric CH <jats:sub>4</jats:sub> aerobically and assimilates carbon from both CH <jats:sub>4</jats:sub> and CO <jats:sub>2</jats:sub> . Its estimated specific affinity for CH <jats:sub>4</jats:sub> (a <jats:sup>0</jats:sup> <jats:sub>s</jats:sub> ) is the highest for any cultivated methanotroph. However, growth on ambient air was also confirmed for <jats:italic>Methylocapsa acidiphila</jats:italic> and <jats:italic>Methylocapsa aurea</jats:italic> , close relatives with a lower specific affinity for CH <jats:sub>4</jats:sub> , suggesting that the ability to utilize atmospheric CH <jats:sub>4</jats:sub> for growth is more widespread than previously believed. The closed genome of <jats:italic>M. gorgona</jats:italic> MG08 encodes a single particulate methane monooxygenase, the serine cycle for assimilation of carbon from CH <jats:sub>4</jats:sub> and CO <jats:sub>2</jats:sub> , and CO <jats:sub>2</jats:sub> fixation via the recently postulated reductive glycine pathway. It also fixes dinitrogen and expresses the genes for a high-affinity hydrogenase and carbon monoxide dehydrogenase, suggesting that atmospheric CH <jats:sub>4</jats:sub> oxidizers harvest additional energy from oxidation of the atmospheric trace gases carbon monoxide (0.2 p.p.m.v.) and hydrogen (0.5 p.p.m.v.). </jats:p>