Abstract
Nitrite-dependent anaerobic methane oxidation (n-damo), which couples the anaerobic oxidation of methane to denitrification, is a recently discovered process mediated by “Candidatus Methylomirabilis oxyfera.” M. oxyfera is affiliated with the “NC10” phylum, a phylum having no members in pure culture. Based on the isotopic labeling experiments, it is hypothesized that M. oxyfera has an unusual intra-aerobic pathway for the production of oxygen via the dismutation of nitric oxide into dinitrogen gas and oxygen. In addition, the bacterial species has a unique ultrastructure that is distinct from that of other previously described microorganisms. M. oxyfera-like sequences have been recovered from different natural habitats, suggesting that the n-damo process potentially contributes to global carbon and nitrogen cycles. The n-damo process is a process that can reduce the greenhouse effect, as methane is more effective in heat-trapping than carbon dioxide. The n-damo process, which uses methane instead of organic matter to drive denitrification, is also an economical nitrogen removal process because methane is a relatively inexpensive electron donor. This mini-review summarizes the peculiar microbiology of M. oxyfera and discusses the potential ecological importance and engineering application of the n-damo process.
Highlights
Methane (CH4) is an important greenhouse gas, which has, so far, contributed an estimated 20% to global warming (Knittel and Boetius, 2009)
Several peculiar properties of the n-damo process have been discovered that make anaerobic methane oxidation (AMO) of particular interest to those interested in microbiology, ecology, and environmental engineering: (i) the discovery of a new species (“Candidatus Methylomirabilis oxyfera”) linking the carbon and nitrogen cycles (Ettwig et al, 2010; Wu et al, 2011a), (ii) the potential contribution of the n-damo process to reduction of global warming via oxidization of methane to carbon dioxide (CO2), and (iii) the potential application of n-damo for nitrogen removal from wastewater by using methane instead of organic matter as an electron donor to drive denitrification. This mini-review summarizes the microbiology of the n-damo process, including the phylogenetic affiliations, physiological and ultrastructural properties of M. oxyfera, and the molecular mechanisms of its intra-aerobic metabolism
Despite the fact that M. oxyfera has the ability to use O2 for methane oxidation, the addition of either 2 or 8% O2 was found to have an overall detrimental effect on this bacterial species (Luesken et al, 2012). These results suggest that M. oxyfera cannot use external O2 to oxidize methane and its O2 production and consumption is a tightly controlled process
Summary
Methane (CH4) is an important greenhouse gas, which has, so far, contributed an estimated 20% to global warming (Knittel and Boetius, 2009). In 2006, a new AMO process, nitrite-dependent anaerobic methane oxidation (n-damo), which couples AMO to denitrification, was discovered in an enrichment culture (Raghoebarsing et al, 2006). This mini-review discusses the potential ecological importance of the n-damo process in natural ecosystems and the application of the process for wastewater nitrogen removal.
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