Widespread soil bacterium that oxidizes atmospheric methane

The global atmospheric level of methane (CH(4)), 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(4) from the atmosphere, but so far, bacteria that can grow on atmospheric CH(4) 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(4) [1.86 parts per million volume (p.p.m.v.)]. This organism, named Methylocapsa gorgona, is globally distributed in soils and closely related to uncultured members of the upland soil cluster α. CH(4) oxidation experiments and (13)C-single cell isotope analyses demonstrated that it oxidizes atmospheric CH(4) aerobically and assimilates carbon from both CH(4) and CO(2). Its estimated specific affinity for CH(4) (a(0)(s)) is the highest for any cultivated methanotroph. However, growth on ambient air was also confirmed for Methylocapsa acidiphila and Methylocapsa aurea, close relatives with a lower specific affinity for CH(4), suggesting that the ability to utilize atmospheric CH(4) for growth is more widespread than previously believed. The closed genome of M. gorgona MG08 encodes a single particulate methane monooxygenase, the serine cycle for assimilation of carbon from CH(4) and CO(2), and CO(2) 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(4) 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.).