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.).