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Methane-dependent complete denitrification primarily involves nitrate reduction to nitrite by ANME-2d archaea and nitrite reduction to dinitrogen by Methylomirabilis bacteria. ' Candidatus Methylomirabilis sinica' integrates the divisional labor. Physiological traits of this bacterium potentially enable the simultaneous reduction of N 2 O and CH 4 emissions. This forum article explores these traits and possible microbial mechanisms for co-reduction, providing guidance for greenhouse gas management strategies. [ABSTRACT FROM AUTHOR]

Methane-dependent denitrification links the global nitrogen and methane cycles. Since its initial discovery in 2006, this process has been understood to involve a division of labor between an archaeal group and a bacterial group, which sequentially perform nitrate and nitrite reduction, respectively. Yao et al. have now revised this paradigm by identifying a Methylomirabilis bacterium capable of performing methane-dependent complete denitrification on its own. [ABSTRACT FROM AUTHOR]

The atmospheric concentration of the potent greenhouse gases methane and nitrous oxide (N 2 O) has increased drastically during the last century. Methylomirabilis bacteria can play an important role in controlling the emission of these two gases from natural ecosystems, by oxidizing methane to CO 2 and reducing nitrite to N 2 without producing N 2 O. These bacteria have an anaerobic metabolism, but are proposed to possess an oxygen-dependent pathway for methane activation. Methylomirabilis bacteria reduce nitrite to NO, and are proposed to dismutate NO into O 2 and N 2 by a putative NO dismutase (NO-D). The O 2 produced in the cell can then be used to activate methane by a particulate methane monooxygenase. So far, the metabolic model of Methylomirabilis bacteria was based mainly on (meta)genomics and physiological experiments. Here we applied a complexome profiling approach to determine which of the proposed enzymes are actually expressed in Methylomirabilis lanthanidiphila. To validate the proposed metabolic model, we focused on enzymes involved in respiration, as well as nitrogen and carbon transformation. All complexes suggested to be involved in nitrite-dependent methane oxidation, were identified in M. lanthanidiphila , including the putative NO-D. Furthermore, several complexes involved in nitrate reduction/nitrite oxidation and NO reduction were detected, which likely play a role in detoxification and redox homeostasis. In conclusion, complexome profiling validated the expression and composition of enzymes hypothesized to be involved in the energy, methane and nitrogen metabolism of M. lanthanidiphila , thereby further corroborating their unique metabolism involved in the environmentally relevant process of nitrite-dependent methane oxidation. Unlabelled Image • Methylomirabilis bacteria perform nitrite-dependent anaerobic methane oxidation. • Strikingly they possess the oxygen-dependent methane oxidation pathway. • They are proposed to produce intracellular oxygen by putative nitric oxide dismutase. • Proteomics-based complexome profiling validated the proposed metabolic model. • Apparent redundancies in nitrogen cycling proteins to maintain redox balance were detected. [ABSTRACT FROM AUTHOR]

The reject water of anaerobic digestors still contains high levels of methane and ammonium that need to be treated before these effluents can be discharged to surface waters. Simultaneous anaerobic methane and ammonium oxidation performed by nitrate/nitrite-dependent anaerobic methane-oxidizing(N-damo) microorganisms and anaerobic ammonium-oxidizing(anammox) bacteria is considered a potential solution to this challenge. Here, a stable coculture of N-damo archaea, N-damo bacteria, and anammox bacteria was obtained in a sequencing batch reactor fed with methane, ammonium, and nitrite. Nitrite and ammonium removal rates of up to 455 mg N-NO2− L−1 day−1 and 228 mg N-NH4+ L−1 were reached. All nitrate produced by anammox bacteria (57 mg N-NO3− L−1 day−1) was consumed, leading to a nitrogen removal efficiency of 97.5%. In the nitrite and ammonium limited state, N-damo and anammox bacteria each constituted about 30–40% of the culture and were separated as granules and flocs in later stages of the reactor operation. The N-damo archaea increased up to 20% and mainly resided in the granular biomass with their N-damo bacterial counterparts. About 70% of the nitrite in the reactor was removed via the anammox process, and batch assays confirmed that anammox activity in the reactor was close to its maximal potential activity. In contrast, activity of N-damo bacteria was much higher in batch, indicating that these bacteria were performing suboptimally in the sequencing batch reactor, and would probably be outcompeted by anammox bacteria if ammonium was supplied in excess. Together these results indicate that the combination of N-damo and anammox can be implemented for the removal of methane at the expense of nitrite and nitrate in future wastewater treatment systems. [ABSTRACT FROM AUTHOR]

Nitrite-dependent methane-oxidizing bacteria couple the reduction of nitrite to the oxidation of methane via a unique oxygen-producing pathway. This process is carried out by genus Methylomirabilis bacteria that belong to the NC10 phylum. Contrary to other known anaerobic methane oxidizers, they do not employ the reverse methanogenesis pathway for methane activation, but a canonical particulate methane monooxygenase similar to those used by aerobic methanotrophs. Methylomirabilis-like bacteria are detected in many natural and manmade ecosystems, but their physiology is not well understood. Here, using continuous cultivation techniques, batch activity assays, and state of the art membrane-inlet mass spectrometry, we determined growth rate, doubling time, and methane and nitrite affinities of the nitrite-dependent methane-oxidizing bacterium 'Candidatus Methylomirabilis lanthanidiphila'. Our results provide insight into understanding the interactions of these microorganisms with methanotrophs, and other nitrite-reducing microorganisms such as anaerobic ammonium oxidizing bacteria. Furthermore, our data can be used in modelling studies as well as wastewater treatment plant design. [ABSTRACT FROM AUTHOR]