A new pathway for nitrite-driven anaerobic methane oxidation by oxygenic bacteria has been discovered. This pathway, involving the bacterium 'Candidatus Methylomirabilis oxyfera', allows methane to be oxidized in the absence of oxygen, using nitrite as an electron acceptor. The genome of this bacterium was sequenced and analyzed, revealing that it encodes the aerobic pathway for methane oxidation, but lacks genes for dinitrogen production. Instead, it converts two nitric oxide molecules into dinitrogen and oxygen, which are used to oxidize methane. This discovery expands our understanding of hydrocarbon degradation under anoxic conditions and explains the biochemical mechanism of a poorly understood freshwater methane sink. The findings suggest that oxygen may have been available to microbial metabolism before the evolution of oxygenic photosynthesis. The study also highlights the importance of nitrogen oxides in early Earth's geochemical cycles and provides insights into the evolution of metabolic pathways. The bacterium, which is a member of the NC10 phylum, is capable of anaerobic growth and produces oxygen for aerobic methane oxidation. The study provides a detailed analysis of the genome, transcriptome, and proteome of this bacterium, revealing its unique metabolic capabilities and potential ecological significance. The research has important implications for understanding the role of microbial communities in the global carbon and nitrogen cycles.A new pathway for nitrite-driven anaerobic methane oxidation by oxygenic bacteria has been discovered. This pathway, involving the bacterium 'Candidatus Methylomirabilis oxyfera', allows methane to be oxidized in the absence of oxygen, using nitrite as an electron acceptor. The genome of this bacterium was sequenced and analyzed, revealing that it encodes the aerobic pathway for methane oxidation, but lacks genes for dinitrogen production. Instead, it converts two nitric oxide molecules into dinitrogen and oxygen, which are used to oxidize methane. This discovery expands our understanding of hydrocarbon degradation under anoxic conditions and explains the biochemical mechanism of a poorly understood freshwater methane sink. The findings suggest that oxygen may have been available to microbial metabolism before the evolution of oxygenic photosynthesis. The study also highlights the importance of nitrogen oxides in early Earth's geochemical cycles and provides insights into the evolution of metabolic pathways. The bacterium, which is a member of the NC10 phylum, is capable of anaerobic growth and produces oxygen for aerobic methane oxidation. The study provides a detailed analysis of the genome, transcriptome, and proteome of this bacterium, revealing its unique metabolic capabilities and potential ecological significance. The research has important implications for understanding the role of microbial communities in the global carbon and nitrogen cycles.