Methylotropicum kingii" showing aerobic methanotrophy was discovered thus suggesting methanotrophy to be present in the four bacterial phyla. In some cases, aerobic methane oxidation can take place in anoxic environments. "Candidatus Methylomirabilis oxyfera" belongs to the phylum NC10 bacteria, and can catalyze nitrite reduction through an "intra-aerobic" pathway, in which internally produced oxygen is used to oxidise methane. In clear water lakes, methanotrophs can live in the anoxic water column, but receive oxygen from photosynthetic organisms, which they then directly consume to oxidize methane. No aerobic methanotrophic archaea are known. Anaerobic Under anoxic conditions, methanotrophs use different electron acceptors for methane oxidation. This can happen in anoxic habitats such as marine or lake sediments, oxygen minimum zones, anoxic water columns, rice paddies and soils. Some specific methanotrophs can reduce nitrate, nitrite, iron, sulfate, or manganese ions and couple that to methane oxidation without syntrophic partner. Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing archaea and sulfate-reducing bacteria. This type of anaerobic oxidation of methane (AOM) mainly occurs in anoxic marine sediments. The exact mechanism is still a topic of debate but the most widely accepted theory is that the archaea use the reversed methanogenesis pathway to produce carbon dioxide and another, unknown intermediate, which is then used by the sulfate-reducing bacteria to gain energy from the reduction of sulfate to hydrogen sulfide and water. The anaerobic methanotrophs are not related to the known aerobic methanotrophs; the closest cultured relatives to the anaerobic methanotrophs are the methanogens in the order Methanosarcinales. Special species Methylococcus capsulatus is used to produce animal feed from natural gas. In 2010 a new bacterium Candidatus Methylomirabilis oxyfera from the phylum NC10 was identified that can couple the anaerobic oxidation of methane to nitrite reduction without the need for a syntrophic partner. Based on studies of Ettwig et al., it is believed that M. oxyfera oxidizes methane anaerobically by utilizing oxygen produced internally from the dismutation of nitric oxide into nitrogen and oxygen gas. Taxonomy Many methanotrophic cultures have been isolated and formally characterized over the past 5 decades, starting with the classical study of Whittenbury (Whittenbury et al., 1970). Currently, 18 genera of cultivated aerobic methanotrophic Gammaproteobacteria and 5 genera of Alphaproteobacteria are known, represented by approx. 60 different species. Methane oxidation Methanotrophs oxidize methane by first initiating reduction of an oxygen atom to H2O2 and transformation of