Key Physiology of a Nitrite-Dependent Methane-Oxidizing Enrichment Culture

Nitrite-dependent methane-oxidizing bacteria couple the reduction of nitrite to the oxidation of methane via a unique oxygen-producing pathway. This process is carried out by members of the genus Methylomirabilis that belong to the NC10 phylum. Contrary to other known anaerobic methane oxidizers, they do not employ the reverse methanogenesis pathway for methane activation but instead a canonical particulate methane monooxygenase similar to those used by aerobic methanotrophs. Methylomirabilis-like bacteria are detected in many natural and manmade ecosystems, but their physiology is not well understood. Here, using continuous cultivation techniques, batch activity assays, and state-of-the-art membrane-inlet mass spectrometry, we determined growth rate, doubling time, and methane and nitrite affinities of the nitrite-dependent methane-oxidizing bacterium Candidatus Methylomirabilis lanthanidiphila. Our results provide insight into understanding the interactions of these microorganisms with methanotrophs and other nitrite-reducing microorganisms, such as anaerobic ammonium-oxidizing bacteria. Furthermore, our data can be used in modeling studies as well as wastewater treatment plant design. IMPORTANCE Methane is an important greenhouse gas with a radiative forcing 28 times that of carbon dioxide over a 100-year time scale. The emission of methane to the atmosphere is controlled by aerobic and anaerobic methanotrophs, which are microorganisms that are able to oxidize methane to conserve energy. While aerobic methanotrophs have been studied for over a century, knowledge on the physiological characteristics of anaerobic methanotrophs is scarce. Here, we describe kinetic properties of Candidatus Methylomirabilis lanthanidiphila, a nitrite-dependent methane-oxidizing microorganism, which is ecologically important and can be applied in wastewater treatment.