Intermediates Production in Methane Oxidation Coupled with Denitrification: Current Status, Challenges, and Future Opportunities

Climate warming is a hot environmental issue of global concern. As one of the major methane sinks, the process of methane oxidation coupled with denitrification (MOD) reduces the environmental impact brought by the greenhouse effect and water eutrophication. In addition, as an energy substance, methane can also improve its economic value by transforming into other liquid chemicals. Previous studies on the mechanism of the process have mainly focused on the extracellular electron transfer between species. However, in recent years, the production of intermediates influenced by different factors, and the existence of a large number of acid-producing bacteria and methanogens under anaerobic conditions, has led some researchers to pursue research into a new mechanism of the process. Moreover, the discovery of CO₂ as a potential electron acceptor in products is certainly exciting, being a big opportunity under the ‘carbon neutral’ policy. This review looks back at the development of the MOD process and describes its functional microorganism and mechanism in detail when summarizing the types of microorganisms and intermediates at different oxygen levels, and introduces some traditional and novel biotechnologies, such as metagenomics, meta-transcriptomics, and meta-proteomics, etc., to help explore the novel mechanism of the process of MOD mediated by intermediates.