Nitrite-dependent Anaerobic Methane Oxidation Process Research Articles

Depth-specific distribution and significance of nitrite-dependent anaerobic methane oxidation process in tidal flow constructed wetlands used for treating river water.

Tidal flow constructed wetlands (TF CWs) have been considered an effective approach to treat contaminated river water, as well as a significant role in global matter cycles, especially for carbon and nitrogen. Notably, it has been thought that methane oxidation was completely catalyzed by the aerobic process, ignoring the anaerobic methane oxidation, such as the nitrite-dependent anaerobic methane oxidation (n-damo) process. In our current work, therefore, we used molecular and stable isotopes to investigate the biodiversity, quantity and potential rate of n-damo bacteria in the TF CWs located in the Xisha Wetland Park in the Yangtze River estuary, China. The results revealed that n-damo process was active in the collected soil cores, with a decreasing trend along water depths and rates ranging from 8.48 to 23.45nmol CO2 g-1 dry soil d-1. The n-damo bacterial contributions to CH4 oxidation and N2 production in TF CWs reached 9.49-26.26% and 20.73-47.11%, respectively, suggesting that n-damo bacteria was an important nitrogen and methane sink in the TF CWs, but had been previously overlooked. The copy numbers of total bacterial 16S rRNA and pmoA genes were 1.84-11.21×109 and 0.59-2.72×106 copies g-1 ds, respectively, as the higher abundance was found in the soil at lower water levels during tidal submergence. Diverse n-damo bacterial 16S rRNA gene sequences belonged to group B, C and D were measured, and it was found that group B and C were the most frequently measured n-damo clusters in the TF CWs. In addition, nitrite was the key factor regulating the n-damo bacterial distribution in the TF CWs. This study would broaden our horizons and help us better understand the nitrogen and methane cycles in tidal ecosystems.

Achieving high nitrogen removal efficiency by optimizing nitrite-dependent anaerobic methane oxidation process with growth factors

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a newly discovered bioprocess which uses methane as electron donor to reduce nitrite into dinitrogen. It is a promising clean bioprocess for denitrification in wastewater treatment. However, the low reaction rate and slow growth rate of N-DAMO bacteria within NC10 phylum limit the application of the process. In this study, we chose vitamin, heme, nucleobase and betaine to investigate their short- and long-term effects on N-DAMO bacteria. The concentrations of the growth factors of medium were improved according to the short-term experiments. The results were subsequently verified via long-term inoculations and were applied in a magnetically stirred gas lift reactor (MSGLR). The results indicated that nucleobase and betaine (5.0 and 200 μg L−1, respectively) significantly stimulated the N-DAMO activity, whereas vitamin and heme had no significant effects in the tested concentration ranges. During the long-term incubation, N-DAMO bacteria continuously increased and finally achieved a relative abundance of 14.4% on day 300. Notably, larger aggregates of N-DAMO bacteria were observed at the end of the long-term incubation. And the nitrogen removal rate of the MSGLR increased to 70 mg N L−1 day−1, with the total nitrogen removal efficiency over 99.0%. However, the addition of betaine introduced methyl into the reactors and this made methylotrophs account a considerable part of the bacterial community, which limited the enrichment degree of N-DAMO bacteria. This work will contribute to the engineering application and enrichment of N-DAMO bacteria.

Rapid Start-up of a Nitrite-Dependent Methane Anaerobic Oxidation Reaction Under Static Pressure Conditions

The present study explores the effect of static pressure on the rapid start-up of a nitrite-dependent anaerobic methane oxidation (N-DAMO) process in lab-scale sequencing batch reactors (SBR). A mixture of anaerobic sludge and deep paddy soil with a volume ratio of 1:1 was used as inoculum and the influent of the nitrite (NO2--N) concentration was gradually increased to avoid a toxicity shock. The variation of the NO2--N removal performance and corresponding microbial characteristics were analyzed to evaluate the development of the N-DAMO process. After 120 days of operation, significant N-DAMO phenomena were observed in both the control SBR (R1) with normal pressure and pressurized SBR (R2) with a static pressure of 0.3 MPa. The NO2--N removal rate (measured by NO2--N) of R2 (36.90 mg·(L·d)-1) was 24% higher than that of R1, while the average NO2--N removal rate in the first 4 h of the batch cycle in R2 (0.10 mmol·(L·h)-1) was 186% higher than that of R1. The mean sludge size of R2 was~2-fold larger than that of R1. Sludge in R2 also has a bigger specific surface area, which improves the mass transfer rate of methane and the N-DAMO performance. The specific activity of N-DAMO (measured by N/VSS) reached 0.29 mg·(g·h)-1 in the study period, which is approximately 2 times higher than that of R1. Moreover, the abundance of N-DAMO functional microbes Candidatus Methylomirabilish oxyfera (M. oxyfera) in R2 was 10-fold higher than that of R1. These results indicate that static pressure effectively accelerates the start-up of the N-DAMO process.

The Occurrence of Putative Nitric Oxide Dismutase (Nod) in an Alpine Wetland with a New Dominant Subcluster and the Potential Ability for a Methane Sink.

Recently, a new oxygenic pathway has been proposed based on the disproportionation of NO with putative NO dismutase (Nod). In addition to a new process in nitrogen cycling, this process provides ecological advantages for the degradation of substrates in anaerobic conditions, which is of great significance for wastewater treatment. However, the Nod distribution in aquatic environments is rarely investigated. In this study, we obtained the nod genes with an abundance of 2.38 ± 0.96 × 105 copies per gram of dry soil from the Zoige wetland and aligned the molecular characteristics in the corresponding Nod sequences. These Nod sequences were not only found existing in NC10 bacteria, but were also found forming some other clusters with Nod sequences from a WWTP reactor or contaminated aquifers. Moreover, a new subcluster in the aquifer-similar cluster was even dominant in the Zoige wetland and was named the Z-aquifer subcluster. Additionally, soils from the Zoige wetland showed a high potential rate (10.97 ± 1.42 nmol of CO2 per gram of dry soil per day) for nitrite-dependent anaerobic methane oxidation (N-DAMO) with low abundance of NC10 bacteria, which may suggest a potential activity of Nod in other clusters when considering the dominance of the Z-aquifer subcluster Nod. In conclusion, we verified the occurrence of Nod in an alpine wetland for the first time and found a new subcluster to be dominant in the Zoige wetland. Moreover, this new subcluster of Nod may even be active in the N-DAMO process in this alpine wetland, which needs further study to confirm.

Spatial and temporal distribution of nitrite-dependent anaerobic methane-oxidizing bacteria in an intertidal zone of the East China Sea.

Nitrite-dependent anaerobic methane oxidation (N-DAMO), which couples anaerobic methane oxidation and nitrite reduction, is a recently discovered bioprocess coupling microbial nitrogen and carbon cycles. The discovery of this microbial process challenges the traditional knowledge of global methane sinks and nitrogen losses. In this study, the abundance and activity of N-DAMO bacteria were investigated and their contributions to methane sink and nitrogen loss were estimated in different seasons and different partitions of an intertidal zone of the East China Sea. The results showed that N-DAMO bacteria were extensively and continuously present in the intertidal zone, with the number of cells ranging from 5.5×104 to 2.8×105 copyg-1 soil and the potential activity ranging from 0.52 to 5.7nmol CO2g-1 soilday-1, contributing 5.0-36.6% of nitrite- and sulfate-dependent anaerobic methane oxidation in the intertidal zone. The N-DAMO activity and its contribution to the methane consumption were highest in the spring and in the low intertidal zone. These findings showed that the N-DAMO process is an important methane and nitrogen sink in the intertidal zone and varies with the seasons and the partitions of the intertidal zone.

Reduction of greenhouse gases emissions during anoxic wastewater treatment by strengthening nitrite-dependent anaerobic methane oxidation process

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered process performed by NC10 phylum, which plays an important role in greenhouse gases (GHG) reduction. In this study, co-existence of n-damo bacteria and methanogens was successfully achieved by using upflow anaerobic sludge blanket (UASB) reactor. Reactor with inorganic carbon source (CO2/H2) showed the highest abundance of n-damo bacteria and the highest n-damo potential activity, resulted in its highest nitrogen removal rate. Significant reduction in GHG was obtained after introduction of n-damo process, especially for N2O. Furthermore, GHG emissions decreased with the increase of n-damo bacteria abundance. Community structure analysis found carbon source could influence the diversity of n-damo bacteria indirectly. And phylogenetic analysis showed that all the obtained sequences were assigned to group B, mainly due to in situ production and consumption of CH4.

Anaerobic methane oxidation coupled to nitrite reduction can be a potential methane sink in coastal environments.

In the current study, we investigated nitrite-dependent anaerobic methane oxidation (N-DAMO) as a potential methane sink in the Hangzhou Bay and the adjacent Zhoushan sea area. The potential activity of the N-DAMO process was primarily observed in Hangzhou Bay by means of (13)C-labeling experiments, whereas very low or no potential N-DAMO activity could be detected in the Zhoushan sea area. The measured potential N-DAMO rates ranged from 0.2 to 1.3nmol (13)CO2g(-1) (dry sediment)day(-1), and the N-DAMO potentially contributed 2.0-9.4% to the total microbial methane oxidation in the examined sediments. This indicated that the N-DAMO process may be an alternative pathway in the coastal methane cycle. Phylogenetic analyses confirmed the presence of Candidatus Methylomirabilis oxyfera-like bacteria in all the examined sediments, while the group A members (the dominant bacteria responsible for N-DAMO) were found mainly in Hangzhou Bay. Quantitative PCR showed that the 16S rRNA gene abundance of Candidatus M. oxyfera-like bacteria varied from 5.4×10(6) to 5.0×10(7) copiesg(-1) (dry sediment), with a higher abundance observed in Hangzhou Bay. In addition, the overlying water NO3 (-) concentration and salinity were identified as the most important factors influencing the abundance and potential activity of Candidatus M. oxyfera-like bacteria in the examined sediments. This study showed the evidence of N-DAMO in coastal environments and indicated the importance of N-DAMO as a potential methane sink in coastal environments.

Improvement of mineral nutrient concentrations and pH control for the nitrite-dependent anaerobic methane oxidation process

Abstract A novel biological nitrogen removal process can be developed based on the newly discovered nitrite-dependent anaerobic methane oxidation (n-damo) process. In this work, the short- and long-term effects of mineral nutrients on the n-damo process were investigated by single-factor and orthogonal experiments, respectively. The pH buffering capacities of different media were determined by acid–base titration. KHCO3 and KH2PO4 greatly influenced the activity of n-damo bacteria and the pH changes of the media. An improved n-damo medium was proposed, containing 0.3 g L−1 CaCl2, 0.2 g L−1 MgSO4, 0.3 g L−1 KH2PO4 and 0.2 g L−1 KHCO3. Moreover, the presence of 1% of CO2 in gas could maintain the pH near neutral in the improved medium, which was first estimated in theory and then verified in practice. Finally, these results were applied in an n-damo reactor. The nitrogen removal rate was slightly increased (from 10.0 ± 1.2 to 10.8 ± 1.4 mg N L−1 d−1), and the pH was quite stable after the improvement (daily changes from 0.58 ± 0.05 to 0.11 ± 0.02).

Nitrite-dependent anaerobic methane-oxidising bacteria: unique microorganisms with special properties.

Microbial mediated nitrite-dependent anaerobic methane oxidation (N-DAMO), which couples the oxidation of methane to nitrite reduction, is a recently discovered process. The discovery of N-DAMO process makes great contributions to complete the biogeochemical cycles of carbon and nitrogen, and to develop novel economic biotechnology for simultaneous carbon and nitrogen removal. This process is catalysed by the unique bacterium "Candidatus Methylomirabilis oxyfera" (M. oxyfera), which belongs to the candidate phylum NC10, a phylum having no members in pure culture. In recent years, some microbiological properties of M. oxyfera have been unravelled. The most prominent examples are the discoveries of the special ultrastructure (star-like) of the cell shape and the unique chemical composition (10MeC16:1Δ7) of M. oxyfera that have not been found in other bacteria yet. More importantly, a new intra-aerobic pathway was discovered in M. oxyfera. It seems that M. oxyfera produces oxygen intracellularly by the conversion of two nitric oxide molecules to dinitrogen gas and oxygen, and the produced oxygen is then used for methane oxidation and normal respiration. The current paper is a systematic review in the microbiological properties of M. oxyfera, especially for its special properties.

Distribution and environmental significance of nitrite-dependent anaerobic methane-oxidising bacteria in natural ecosystems.

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a recently discovered process that is performed by "Candidatus Methylomirabilis oxyfera" (M. oxyfera). This process constitutes a unique association between the two major global elements essential to life, carbon and nitrogen, and may act as an important and overlooked sink of the greenhouse gas methane. In recent years, more and more studies have reported the distribution of M. oxyfera-like bacteria and the occurrence of N-DAMO process in different natural ecosystems, including freshwater lakes, rivers, wetlands and marine ecosystems. Previous studies have estimated that a total of 2%-6% of current worldwide methane flux in wetlands could be consumed via the N-DAMO process. These findings indicate that N-DAMO is indeed a previously overlooked methane sink in natural ecosystems. Given the worldwide increase in anthropogenic nitrogen pollution, the N-DAMO process as a methane sink in reducing global warming could become more important in the future. The present mini-review summarises the current knowledge of the ecological distribution of M. oxyfera-like bacteria and the potential importance of the N-DAMO process in reducing methane emissions in various natural ecosystems. The potential influence of environmental factors on the N-DAMO process is also discussed.

Microbiology, ecology, and application of the nitrite-dependent anaerobic methane oxidation process

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.