Acetate Production from Anaerobic Oxidation of Methane via Intracellular Storage Compounds

There is great interest in microbial conversion of methane, an abundant resource, into valuable liquid chemicals. While aerobic bioconversion of methane to liquid chemicals has been reported, studies of anaerobic methane bioconversion to liquid chemicals are rare. Here we show that a microbial culture dominated by Candidatus 'Methanoperedens nitroreducens', an anaerobic methanotrophic archaeon, anaerobically oxidizes methane to produce acetate, indirectly via reaction intermediate(s), when nitrate or nitrite is supplied as an electron acceptor under a rate-limiting condition. Isotopic labeling tests showed that acetate was produced from certain intracellular storage compounds that originated from methane. Fluorescence in situ hybridization and Nile red staining demonstrated that polyhydroxyalkanoate in M. nitroreducens was likely one of the intracellular storage compounds for acetate production, along with glycogen. Acetate is a common substrate for the production of more valuable chemicals. The microbial conversion discovered in this study potentially enables a new approach to the use of methane as a feedstock for the chemical market.