Active pathways of anaerobic methane oxidation across contrasting riverbeds

Effects of drainage and long-term tillage on greenhouse gas fluxes in a natural wetland: insights from microbial mechanisms

BACKGROUND

The conversion of natural wetlands to agricultural land through drainage contributes to 62% of the global wetland loss. Such conversion significantly alters greenhouse gas (GHG) fluxes, yet the underlying mechanisms of GHG fluxes resulting from drainage and long-term tillage practices remain highly uncertain. In this study, we measured GHG fluxes of a natural reed wetland (referred to as "Wetland") and a drained wetland that used as farmland (referred to as "Dryland").

RESULTS

The results demonstrated that annual cumulative N2O and CO2 fluxes in Dryland were 282.77% and 53.79% higher than those in Wetland, respectively. However, CH4 annual cumulative fluxes decreased from 12,669.45 ± 564.69 kg·ha- 1 to 8,238.40 ± 207.72 kg·ha- 1 in Dryland compared to Wetland. The global warming potential (GWP) showed no significant difference between Dryland and Wetland, with comparable average rates of 427.50 ± 48.83 and 422.21 ± 73.59 mg·CO2-eq·m- 2·h- 1, respectively. Metagenomic analysis showed a decrease in the abundance of acetoclastic methanogens and their functional genes responsible for CH4 production. Functional genes related to CH4 oxidation (pmoA) and gene related to N2O reduction (nosZ) exhibited a substantial sensitivity to variations in TOC concentration (p < 0.05). Candidatus Methylomirabilis, belonging to the NC10 phylum, was identified as the dominant methanotroph and accounted for 49.26% of the methanotrophs. Its relative abundance was significantly higher in Dryland than in Wetland, as the nitrogenous fertilizer applied in Dryland acted as an electron acceptor, with the nearby Wetland produced CH4 serving as an electron donor. This suggests that Dryland may act as a CH4 sink, despite the significant enhancement in CO2 and N2O fluxes.

CONCLUSIONS

In conclusion, this study provides insights into the influence of drainage and long-term tillage on GHG fluxes in wetlands and their contribution to global warming.

Denitrifying anaerobic methane oxidation activity and microbial mechanisms in Riparian zone soils of the Yulin River, a tributary of the Three Gorges Reservoir

Riparian zones are recognized as major sources of greenhouse gas emissions, particularly methane (CH4). Denitrifying anaerobic methane oxidation (DAMO) has garnered growing attention due to its significant contribution to mitigating CH4 emissions in wetland environments. Nonetheless, the specific role and microbial mechanisms of DAMO in controlling CH4 release within riparian zones are still not well comprehended. This study employed isotopic labeling experiments to measure the nitrate-dependent anaerobic methane oxidation (NaDAMO) and nitrite-dependent anaerobic methane oxidation (NiDAMO) potential of soil samples from riparian zones that were collected during different hydrological cycles. Moreover, soil physicochemical properties, DAMO activity, and microbial abundance were integrated to analyze the key factors and mechanisms influencing DAMO in riparian zone soils. The isotope tracer results showed that NaDAMO activities (1.41-11.93 nmol 13CO2 g-1day-1) were significantly higher than NiDAMO activities (0.66-9.19 nmol 13CO2 g-1day-1) in the riparian zone (p < 0.05). NiDAMO activities were more strongly influenced by hydrological variations compared to NaDAMO activities, exhibiting higher levels during the discharge period (2.78-9.19 nmol 13CO2 g-1day-1) compared to the impoundment period (0.66-4.10 nmol 13CO2 g-1day-1). The qPCR analysis showed that the gene copies of NaDAMO archaeal mcrA (107 copies g-1) were approximately ten times greater than those of NiDAMO bacterial pmoA (106 copies g-1) in the majority of the sampling sites. Correlation analyses revealed that NiDAMO activity was influenced by soil pH (p < 0.05), while NaDAMO microbes were influenced by temperature, organic carbon, and ammonia nitrogen concentrations (p < 0.05). In summary, this research explored how hydrological changes in the riparian zone influence DAMO activities and their underlying mechanisms, providing a theoretical basis for mitigating CH4 emissions in riparian zones of reservoir regions.

Tidal-driven N2O emission is a stronger resister than CH4 to offset annual carbon sequestration in mangrove ecosystems

The mangrove ecosystems store a significant amount of "blue carbon" to mitigate global climate change, but also serve as hotspots for greenhouse gases (GHGs: CO2, CH4 and N2O) production. The CH4 and N2O emissions offset mangrove carbon benefits, however, the extent of this effect remains inadequately quantified. By applying the 36 h time-series observations and mapping cruises, here we investigated the spatial and temporal distribution of GHGs and their fluxes in Dongzhaigang (DZG) bay, the largest mangrove ecosystem in China, at tidal and monthly scales. The spatiotemporal variation of GHGs were mainly controlled by tidal-forced water mixing, outgassing and multiple biogeochemical processes. Tidal-driven porewater outwelling and sediment resuspension largely explained the excess addition of dissolved GHGs in tidal creeks. These lateral export combined with river input contribute significantly to surrounding water emission. Salinity controls CH4 emission in river-tidal creek-bay continuum, with concentration decreased by ∼100-fold from freshwater to seawater sites. N2O concentration was controlled by substrate supply for both nitrification and denitrification. Overall, the GHGs emissions in tidal creeks equal to 669-39,000 (7521 ± 6401) g CO2-eq/m2/yr (CO2 contributed ∼88-91 %) to atmosphere. In particular, CH4 and N2O contribute 8-366 (124 ± 78) g CO2-eq/m2/yr and 59-2260 (712 ± 525) g CO2-eq/m2/yr, together offsetting 8.7 ± 2.1 % of annual mangrove carbon sequestration, with a larger contribution from N2O (7.4 %). Our findings highlight the importance of simultaneous quantification of non-CO2 GHGs to accurately assess blue carbon capacity.

Response of denitrifying anaerobic methane oxidation processes in freshwater and marine sediments to polyvinyl chloride microplastics

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in mitigating methane (CH4) in natural environments. The increasing presence of microplastics (MPs) in these environments due to human activities is a growing concern. However, the impact of MPs on n-DAMO microorganisms and their role in greenhouse gas regulation, particularly CH4 reduction, remains unclear. This study investigates the effects of polyvinyl chloride (PVC) MPs on n-DAMO activity and the associated microbial communities in freshwater and marine sediments at varying concentrations of (R0/M0-no addition, R1/M1-0.5 %, R2/M2-2%). The results showed that the presence of MPs significantly increased the n-DAMO rate (2.89-3.58 nmol 13CO2 g-1 d-1) compared to the control groups (R0: 1.29 nmol 13CO2 g-1 d-1, M0: 0.11 nmol 13CO2 g-1 d-1), with marine sediments showing a more pronounced response. Additionally, the proportional contribution of nitrate-DAMO processes increased following MP exposure. The presence of PVC MPs also altered the microbial diversity of n-DAMO. Upon the addition of MPs, the microbial community composition of n-DAMO in marine sediments changed more significantly. This study provides the first evidence of a positive impact of PVC MPs on n-DAMO processes, suggesting that the presence of PVC MPs in sediments could potentially contribute to the reduction of CH4 emissions.

Vertical distribution of Candidatus Methylomirabilis and Methanoperedens in agricultural soils

Candidatus Methylomirabilis-related bacteria conduct anaerobic oxidation of methane (AOM) coupling with NO2- reduction, and Candidatus Methanoperedens-related archaea perform AOM coupling with reduction of diverse electron acceptors, including NO3-, Fe (III), Mn (IV) and SO42-. Application of nitrogen fertilization favors the growth of these methanotrophs in agricultural fields. Here, we explored the vertical variations in community structure and abundance of the two groups of methanotrophs in a nitrogen-rich vegetable field via using illumina MiSeq sequencing and quantitative PCR. The retrieved Methylomirabilis-related sequences had 91.12%-97.32% identity to the genomes of known Methylomirabilis species, and Methanoperedens-related sequences showed 85.49%-97.48% identity to the genomes of known Methanoperedens species which are capable of conducting AOM coupling with reduction of NO3- or Fe (III). The Methanoperedens-related archaeal diversity was significantly higher than Methylomirabilis-related bacteria, with totally 74 and 16 operational taxonomic units, respectively. In contrast, no significant difference in abundance between the bacteria (9.19 × 103-3.83 × 105 copies g-1 dry soil) and the archaea (1.55 × 104-3.24 × 105 copies g-1 dry soil) was observed. Furthermore, the abundance of both groups of methanotrophs exhibited a strong vertical variation, which peaked at 30-40 and 20-30 cm layers, respectively. Soil water content and pH were the key factors influencing Methylomirabilis-related bacterial diversity and abundance, respectively. For the Methanoperedens-related archaea, both soil pH and ammonium content contributed significantly to the changes of these archaeal diversity and abundance. Overall, we provide the first insights into the vertical distribution and regulation of Methylomirabilis-related bacteria and Methanoperedens-related archaea in vegetable soils. KEY POINTS: • The archaeal diversity was significantly higher than bacterial. • There was no significant difference in the abundance between bacteria and archaea. • The abundance of bacteria and archaea peaked at 30-40 and 20-30 cm, respectively.

Role and environmental regulation of iron-driven anaerobic methane oxidation in riverine sediment

Iron is an abundant element in the environment and acts as a thermodynamically favorable electron acceptor driving the anaerobic oxidation of methane (AOM). Presently, the role and environmental regulation of iron-driven AOM in rivers, an important source of methane emission, are nearly unknown. Here, we provided direct evidence for iron-driven AOM activity in sediment of a mountainous river (Wuxijiang River, China) through 13C-labeled isotopic experiment. The potential rate of iron-driven AOM ranged between 0.40 and 1.84 nmol 13CO2 g (sediment) d-1, which contributed 36% on average to total AOM activity when combined the potential nitrate- and nitrite-driven AOM rates measured previously. There were significant variations in iron-driven AOM rates among different reaches (upper, middle, and lower) and between seasons (summer and winter). Sediment temperature, pH, and nitrate content were closely associated with the dynamic of AOM activity. Our results indicate that iron-driven AOM has great potential for reducing methane emissions from riverine ecosystems, and suggest the necessity of taking both spatial and temporal scales into account to evaluate the quantitative role of this AOM process.

Methane oxidation driven by multiple electron acceptors in the water level fluctuation zone of the Three Gorges Reservoir area, China

Water level fluctuations in China's Three Gorges Reservoir (TGR) area are typical of many reservoirs and significantly impact water level fluctuation zones (WLFZ), including upstream rivers. Understanding methane oxidation in the TGR-WLFZ is crucial for evaluating the impact of large-scale reservoir construction on global climate change. In this study, we investigated methane oxidation rates in the TGR-WLFZ, focusing on periods of drying and flooding. The highest methane oxidation rates were observed during the drying period, ranging from 35.69 to 56.32 nmol/(g soil)/d, while the lowest rates were recorded during the flooding period, at 11.58 to 11.98 nmol/(g soil)/d, in lab-scale simulated columns. Using 13CH4 labeling experiments, we measured CH4 oxidation potentials for aerobic methane oxidation (AMO) using oxygen and anaerobic oxidation of methane (AOM) using nitrite, nitrate, sulfate, ferric iron, and manganese oxide as electron acceptors at varying concentrations. AMO was the dominant process across all experiments, with potentials ranging from 145.71 to 180.77 nmol 13CO2/(g soil)/d. For AOM, metal-dependent oxidation, particularly with Fe (III) and Mn(IV), was predominant (12.64-17.59 and 3.91-12.69 nmol 13CO2/(g soil)/d, respectively), followed by nitrite and nitrate-dependent pathways (1.49-9.10 nmol 13CO2/(g soil)/d). Sulfate-dependent AOM was limited (1.33-3.27 nmol 13CO2/(g soil)/d). Metagenomic analysis identified key microorganisms responsible for AMO, such as unclassified_f_Methylobacteriaeae and Methylobacterium sp., and for AOM are Ca. Methylomirabilis oxyfera, Ca. Methanoperedens nitroreducens and Ca. Methylomirabilis sp. Complete functional genes and enzymes for the methane oxidation and reverse methanogenesis pathways were obtained in each hydrological period, with the highest content during the drying period and the lowest during flooding. Our study shows that reservoirs, traditionally considered significant sources of methane, may also act as methane sinks. This finding raises new questions: How do different methane oxidation pathways respond to water level fluctuations in reservoirs, and are some pathways more resilient to changes in hydrological conditions?

The Effects of Model Insoluble Copper Compounds in a Sedimentary Environment on Denitrifying Anaerobic Methane Oxidation (DAMO) Enrichment

The contribution of denitrifying anaerobic methane oxidation (DAMO) as a methane sink across different habitats, especially those affected by anthropogenic activities, remains unclear. Mining and industrial and domestic use of metals/metal-containing compounds can all cause metal contamination in freshwater ecosystems. Precipitation of metal ions often limits their toxicity to local microorganisms, yet microbial activity may also cause the redissolution of various precipitates. In contrast to most other studies that apply soluble metal compounds, this study investigated the responses of enriched DAMO culture to model insoluble copper compounds, malachite and covellite, in simulated sedimentary environments. Copper ≤ 0.22 µm from covellite appeared to cause immediate inhibition in 10 h. Long-term tests (54 days) showed that apparent methane consumption was less impacted by various levels of malachite and covellite than soluble copper. However, the medium-/high-level malachite and covellite caused a 46.6-77.4% decline in denitrification and also induced significant death of the representative DAMO microorganisms. Some enriched species, such as Methylobacter tundripaludum, may have conducted DAMO or they may have oxidized methane aerobically using oxygen released by DAMO bacteria. Quantitative polymerase chain reaction analysis suggests that Candidatus Methanoperedens spp. were less affected by covellite as compared to malachite while Candidatus Methylomirabilis spp. responded similarly to the two compounds. Under the stress induced by copper, DAMO archaea, Planctomycetes spp. or Phenylobacterium spp. synthesized PHA/PHB-like compounds, rendering incomplete methane oxidation. Overall, the findings suggest that while DAMO activity may persist in ecosystems previously exposed to copper pollution, long-term methane abatement capability may be impaired due to a shift of the microbial community or the inhibition of representative DAMO microorganisms.

Methane Production Is More Sensitive to Temperature Increase than Aerobic and Anaerobic Methane Oxidation in Chinese Paddy Soils

Methane emissions from paddy fields can increase under future warming scenarios. Nevertheless, a comprehensive comparison of the temperature sensitivity of methane-related microbial processes remains elusive. Here, we revealed that the temperature sensitivity of methane production (activation energy (Ea) = 0.94 eV; 95% confidence interval (CI), 0.78-1.10 eV) and aerobic (Ea = 0.49 eV; 95% CI, 0.34-0.65 eV) and anaerobic (Ea = 0.46 eV; 95% CI, 0.30-0.62 eV) methane oxidation exhibited notable spatial heterogeneity across 12 Chinese paddy fields spanning 35° longitude and 18° latitude. In addition, the Ea values of aerobic and anaerobic methane oxidation were significantly positively and negatively correlated to the latitude, respectively, while there was no significant correlation between the Ea of methane production and the latitude. Overall, there were no soil factors that had a significant effect on the Ea of methane production. The Ea of aerobic methane oxidation was primarily influenced by the contents of ammonium and clay, whereas the Ea of anaerobic methane oxidation was mainly influenced by the conductivity. Despite the variation, the overall temperature sensitivity of methane production was significantly higher than that of oxidation at a continental scale; therefore, an increase in the emission of methane from paddy fields will be predicted under future warming. Taken together, our study revealed the characteristics of temperature sensitivity of methane production and aerobic and anaerobic methane oxidation simultaneously in Chinese paddy fields, highlighting the potential roles of soil factors in influencing temperature sensitivity.

Anaerobic oxidation of methane driven by different electron acceptors: A review

Methane, the most significant reduced form of carbon on Earth, acts as a crucial fuel and greenhouse gas. Globally, microbial methane sinks encompass both aerobic oxidation of methane (AeOM), conducted by oxygen-utilizing methanotrophs, and anaerobic oxidation of methane (AOM), performed by anaerobic methanotrophs employing various alternative electron acceptors. These electron acceptors involved in AOM include sulfate, nitrate/nitrite, humic substances, and diverse metal oxides. The known anaerobic methanotrophic pathways comprise the internal aerobic oxidation pathway found in NC10 bacteria and the reverse methanogenesis pathway utilized by anaerobic methanotrophic archaea (ANME). Diverse anaerobic methanotrophs can perform AOM independently or in cooperation with symbiotic partners through several extracellular electron transfer (EET) pathways. AOM has been documented in various environments, including seafloor methane seepages, coastal wetlands, freshwater lakes, soils, and even extreme environments like hydrothermal vents. The environmental activities of AOM processes, driven by different electron acceptors, primarily depend on the energy yields, availability of electron acceptors, and environmental adaptability of methanotrophs. It has been suggested that different electron acceptors driving AOM may occur across a wider range of habitats than previously recognized. Additionally, it is proposed that methanotrophs have evolved flexible metabolic strategies to adapt to complex environmental conditions. This review primarily focuses on AOM, driven by different electron acceptors, discussing the associated reaction mechanisms and the habitats where these processes are active. Furthermore, it emphasizes the pivotal role of AOM in mitigating methane emissions.

Active role of iron-dependent AOM in paddy fields under different long-term fertilizer management schemes

Iron-dependent anaerobic oxidation of methane (iron-AOM) has recently been reported to occur in paddy soils, but its actual role and regulation remain unclear. Here, we confirmed the occurrence of iron-AOM at different layers of paddy soils (0-10 cm, 10-20 cm, and 30-40 cm) across tillering, elongation, flowering, and ripening periods under three long-term fertilizer management schemes (CK-unamended, CF-chemical fertilizer, and CFS-chemical fertilizer with straw). The iron-AOM activity contributed 41 % to total AOM, which was greater than that of nitrite- (32 %) and nitrate-AOM (27 %). The iron-AOM activity varied significantly with soil layers, growth periods and fertilizer types, with layer being the most important variable. Soil moisture content and organic carbon content were most significant influencing factors on the AOM activity, and a Candidatus Methanoperedens ferrireducens-like lineage potentially catalyzed iron-AOM. Our results suggest that iron-AOM has an important potential for mitigating methane emissions from rice paddies.

Intermittent aeration mitigating carbon emission from landfills with gas-water joint regulation

Landfill is a significant source of atmospheric CH4 and CO2 emissions. In this study, four landfill reactor systems were constructed to investigate the effects of different ventilation methods, including continuous aeration (20 h d-1) and intermittent aeration (continuous aeration for 4 h d-1 and 2 h of aeration every 12 h, twice a day), on properties of landfilled waste and emissions of CH4 and CO2, in comparison to a traditional landfill. Compared with continuous aeration, intermittent aeration could reduce the potential global warming effect of the CH4 and CO2 emissions, especially multiple intermittent aeration. The CH4 and CO2 emissions could be predicted by the multiple linear regression model based on the contents of carbon, sulfur and/or pH during landfill stabilization. Both intermittent and continuous aeration could enhance the methane oxidation activity of landfilled waste. The aerobic methane oxidation activity of landfilled waste reached the maximums of 50.77-73.78 μg g-1 h-1 after aeration for 5 or 15 d, which was higher than the anaerobic methane oxidation activity (0.45-1.27 μg g-1 h-1). CO2 was the predominant form of organic carbon loss in the bioreactor landfills. Candidatus Methylomirabilis, Methylobacter, Methylomonas and Crenothrix were the main methane-oxidating microorganisms (MOM) in the landfills. Total, NO2--N, pH and Fe3+ were the main environmental variables influencing the MOM community, among which NO2--N and pH had the significant impact on the MOM community. Partial least squares path modelling indicated that aeration modes mainly influenced the emissions of CH4 and CO2 by affecting the degradation of landfilled waste, environmental variables and microbial activities. The results would be helpful for designing aeration systems to reduce the emissions of CH4 and CO2, and the cost during landfill stabilization.

Microplastics promote methane emission in estuarine and coastal wetlands

Increasing microplastic (MP) pollution poses significant threats to estuarine and coastal ecosystems. However, the effects of MPs on the emission of methane (CH4), a potent greenhouse gas, within these ecosystems and the underlying regulatory mechanisms have not been elucidated. Here, a combination of 13C stable isotope-based method and molecular techniques was applied to investigate how conventional petroleum-based MPs [polyethylene (PE) and polyvinyl chloride (PVC)] and biodegradable MPs [polylactic acid (PLA) and polyadipate/butylene terephthalate (PBAT)] regulate CH4 production and consumption and thus affect CH4 emission dynamics in estuarine and coastal wetlands. Results indicated that both conventional and biodegradable MPs enhanced the emission of CH4 (P < 0.05), with the promoting effect being more significant for biodegradable MPs. However, the mechanisms by which conventional and biodegradable MPs promote CH4 emissions were different. Specifically, conventional MPs stimulated the emission of CH4 by inhibiting the processes of CH4 consumption, but had no significant effect on CH4 production rate. Nevertheless, biodegradable MPs promoted CH4 emissions via accelerating the activities the methanogens while inhibiting the oxidation of CH4, thus resulting in a higher degree of promoting effect on CH4 emissions than conventional MPs. Consistently, quantitative PCR further revealed a significant increase in the abundance of methyl-coenzyme M reductase gene (mcrA) of methanogens under the exposure of biodegradable MPs (P < 0.05), but not conventional MPs. Furthermore, the relative abundance of most genes involved in CH4 oxidation exhibited varying degrees of reduction after exposure to all types of MPs, based on metagenomics data. This study reveals the effects of MPs on CH4 emissions in estuarine and coastal ecosystems and their underlying mechanisms, highlighting that the emerging biodegradable MPs exhibited a greater impact than conventional MPs on promoting CH4 emissions in these globally important ecosystems, thereby accelerating global climate change.

Methanomethylovorans are the dominant dimethylsulfide-degrading methanogens in gravel and sandy river sediment microcosms

BACKGROUND

Rivers and streams are important components of the global carbon cycle and methane budget. However, our understanding of the microbial diversity and the metabolic pathways underpinning methylotrophic methane production in river sediments is limited. Dimethylsulfide is an important methylated compound, found in freshwater sediments. Yet, the magnitude of DMS-dependent methanogenesis nor the methanogens carrying out this process in river sediments have been explored before. This study addressed this knowledge gap in DMS-dependent methanogenesis in gravel and sandy river sediments.

RESULTS

Significant methane production via DMS degradation was found in all sediment  microcosms. Sandy, less permeable river sediments had higher methane yields (83 and 92%) than gravel, permeable sediments (40 and 48%). There was no significant difference between the methanogen diversity in DMS-amended gravel and sandy sediment microcosms, which Methanomethylovorans dominated. Metagenomics data analysis also showed the dominance of Methanomethylovorans and Methanosarcina. DMS-specific methyltransferase genes (mts) were found in very low relative abundances whilst the methanol-, trimethylamine- and dimethylamine-specific methyltransferase genes (mtaA, mttB and mtbB) had the highest relative abundances, suggesting their involvement in DMS-dependent methanogenesis.

CONCLUSIONS

This is the first study demonstrating a significant potential for DMS-dependent methanogenesis in river sediments with contrasting geologies. Methanomethylovorans were the dominant methylotrophic methanogen in all river sediment microcosms. Methyltransferases specific to methylotrophic substrates other than DMS are likely key enzymes in DMS-dependent methanogenesis, highlighting their versatility and importance in the methane cycle in freshwater sediments, which would warrant further study.

Simultaneous methane mitigation and nitrogen removal by denitrifying anaerobic methane oxidation in lake sediments

Methane (CH4) is a potent greenhouse gas, with lake ecosystems significantly contributing to its global emissions. Denitrifying anaerobic methane oxidation (DAMO) process, mediated by NC10 bacteria and ANME-2d archaea, links global carbon and nitrogen cycles. However, their potential roles in mitigating methane emissions and removing nitrogen from lake ecosystems remain unclear. This study explored the spatial variations in activities of nitrite- and nitrate-DAMO and their functional microbes in Changdanghu Lake sediments (Jiangsu Province, China). The results showed that although the average abundance of ANME-2d archaea (5.0 × 106 copies g-1) was significantly higher than that of NC10 bacteria (2.1 × 106 copies g-1), the average potential rates of nitrite-DAMO (4.59 nmol 13CO2 g-1 d-1) and nitrate-DAMO (5.01 nmol 13CO2 g-1 d-1) showed no significant difference across all sampling sites. It is estimated that nitrite- and nitrate-DAMO consumed approximately 6.46 and 7.05 mg CH4 m-2 d-1, respectively, which accordingly achieved 15.07-24.95 mg m-2 d-1 nitrogen removal from the studied lake sediments. Statistical analyses found that nitrite- and nitrate-DAMO activities were both significantly related to sediment nitrate contents and ANME-2d archaeal abundance. In addition, NC10 bacterial and ANME-2d archaeal community compositions showed significant correlations with sediment organic carbon content and water depth. Overall, this study underscores the dual roles of nitrite- and nitrate-DAMO processes in CH4 mitigation and nitrogen elimination and their key environmental impact factors (sediment organic carbon and inorganic nitrogen contents, and water depth) in shallow lake, enhancing the understanding of carbon and nitrogen cycles in freshwater aquatic ecosystems.

Anaerobic oxidation of methane in landfill and adjacent groundwater environments: Occurrence, mechanisms, and potential applications

Landfills remain the predominant means of solid waste management worldwide. Widespread distribution and significant stockpiles of waste in landfills make them a significant source of methane emissions, exacerbating climate change. Anaerobic oxidation of methane (AOM) has been shown to play a critical role in mitigating methane emissions on a global scale. The rich methane and electron acceptor environment in landfills provide the necessary reaction conditions for AOM, making it a potentially low-cost and effective strategy for reducing methane emissions in landfills. However, compared to other anaerobic habitats, research on AOM in landfill environments is scarce, and there is a lack of analysis on the potential application of AOM in different zones of landfills. Therefore, this review summarizes the existing knowledge on AOM and its occurrence in landfills, analyzes the possibility of AOM occurrence in different zones of landfills, discusses its potential applications, and explores the challenges and future research directions for AOM in landfill management. The identification of research gaps and future directions outlined in this review encourages further investigation and advancement in the field of AOM, paving the way for more effective waste stabilization, greenhouse gas reduction, and pollutant mitigation strategies in landfills.

Nitrite-dependent anaerobic methane oxidation (N-DAMO) in global aquatic environments: A review

The vast majority of processes in the carbon and nitrogen cycles are driven by microorganisms. The nitrite-dependent anaerobic oxidation of methane (N-DAMO) process links carbon and nitrogen cycles, offering a novel approach for the simultaneous reduction of methane emissions and nitrite pollution. However, there is currently no comprehensive summary of the current status of the N-DAMO process in natural aquatic environments. Therefore, our study aims to fill this knowledge gap by conducting a comprehensive review of the global research trends in N-DAMO processes in various aquatic environments (excluding artificial bioreactors). Our review mainly focused on molecular identification, global study sites, and their interactions with other elemental cycling processes. Furthermore, we performed a data integration analysis to unveil the effects of key environmental factors on the abundance of N-DAMO bacteria and the rate of N-DAMO process. By combining the findings from the literature review and data integration analysis, we proposed future research perspectives on N-DAMO processes in global aquatic environments. Our overarching goal is to advance the understanding of the N-DAMO process and its role in synergistically reducing carbon emissions and removing nitrogen. By doing so, we aim to make a significant contribution to the timely achievement of China's carbon peak and carbon neutrality targets.

The function and keystone microbiota in typical habitats under the influence of anthropogenic activities in Baiyangdian Lake

Microbe is an essential driver in regulating the biochemical cycles of carbon, nitrogen, and sulfur. In freshwater lake, microbial communities and functions are influenced by multiple factors, especially anthropogenic activities. Baiyangdian Lake consisted of various habitats, and was frequently interfered with human activities. In this study, 16 S rRNA sequencing and metagenomic sequencing were performed to characterize the microbial communities, determine keystone taxa and reveal dominated metabolic functions in typical habitats in Baiyangdian Lake. The results showed that the diversity of microbial community was significantly higher in sediment compared with corresponding water sample. Microbial community showed strong spatial heterogeneity in sediment, and temporal heterogeneity in water. As for different habitats, significantly higher alpha diversity was observed in ecotone, where the interference of human activities was relatively weak. The shared OTUs were distinguished from the keystone taxa, which indicated the uniqueness of microbiota in different ecological habitat. Moreover, the interactions of microbial in ecological restoration area (abandoned fish pond) were relatively simple, suggesting that this ecosystem was relatively fragile compared with others. Based on the metagenomic sequencing, we recognized that the canal, open water, and abandoned fish pond were beneficial for methanogenic and the ecotone might be a hot zone for the oxidation of methane. Notably, most of the microbes that participated in these predominant metabolisms were unclassified, which indicated the hug potential for exploring functional microorganisms in Baiyangdian Lake. This study provided a comprehensive understanding of the ecology characteristics of microbiota in habitats undergoing various human interference in Baiyangdian Lake.

High methane ebullition throughout one year in a regulated central European stream

Ebullition transports large amounts of the potent greenhouse gas methane (CH4 ) from aquatic sediments to the atmosphere. River beds are a main source of biogenic CH4 , but emission estimates and the relative contribution of ebullition as a transport pathway are poorly constrained. This study meets a need for more direct measurements with a whole-year data set on CH4 ebullition from a small stream in southern Germany. Four gas traps were installed in a cross section in a river bend, representing different bed substrates between undercut and slip-off slope. For a comparison, diffusive fluxes were estimated from concentration gradients in the sediment and from measurements of dissolved CH4 in the surface water. The data revealed highest activity with gas fluxes above 1000 ml m- 2  d- 1 in the center of the stream, sustained ebullition during winter, and a larger contribution of ebullitive compared to diffusive CH4 fluxes. Increased gas fluxes from the center of the river may be connected to greater exchange with the surface water, thus increased carbon and nutrient supply, and a higher sediment permeability for gas bubbles. By using stable isotope fractionation, we estimated that 12-44% of the CH4 transported diffusively was oxidized. Predictors like temperature, air pressure drop, discharge, or precipitation could not or only poorly explain temporal variations of ebullitive CH4 fluxes.

Humic substances as electron acceptor for anaerobic oxidation of methane (AOM) and electron shuttle in Mn (IV)-dependent AOM

Anaerobic methanotrophic archaea (ANME) belonging to the family Methanoperedenaceae are crucial for the global carbon cycle and different biogeochemical processes, owing to their metabolic versatility to couple anaerobic oxidation of methane (AOM) with different electron acceptors. A universal feature of Methanoperedenaceae is the abundant genes encoded in their genomes associated with extracellular electron transfer (EET) pathways. Candidatus. 'Methanoperedens manganicus', an archaeon belonging to the family Methanoperedenaceae, was recently enriched in a bioreactor performing AOM coupled with Mn (IV) reduction. Using this EET-capable ANME, we tested the hypothesis in this study that ANME can catalyse the humic-dependent AOM for growth. A two-year incubation showed that AOM activity can be sustained by Ca. 'M. manganicus' consortium in a bioreactor fed only with humic acids and methane. An isotopic mass balance batch test confirmed that the observed AOM was coupled to the reduction of humic acids. The increase of relative abundance of Ca. 'M. manganicus', and the total archaea population in the microbial community suggested that Ca. 'M. manganicus' can grow on methane and humic acids. The observation of humic-dependent AOM led to a subsequent hypothesis that humic acids could be used as the electron shuttle to mediate the EET in dissimilatory Mn (IV) reduction by Ca. 'M. manganicus'. We tested this hypothesis by adding humic acids to a Ca. 'M. manganicus' dominated-culture, which showed that the AOM rate was doubled by the addition of humic acids. X-ray photoelectron spectroscopy (XPS) showed that quinone moieties were consumed when humic acids worked as electron acceptors while remaining stable when functioning as a shuttle for electron transfer. The results of our study suggest that humic acids may serve as electron shuttles to allow ANME to access more electron acceptors through long-range EET.

Equal importance of humic acids and nitrate in driving anaerobic oxidation of methane in paddy soils

Methane (CH4) is both generated and consumed in paddy soils, where anaerobic oxidation of methane (AOM) serves as a crucial process for mitigating CH4 emissions. Although the participation of humic acids (HA) and nitrate in AOM has been recognized, their relative roles and significance in paddy soils remain insufficiently investigated. In this study, we explored the potential activity of AOM driven by HA and nitrate, as well as the composition of archaeal communities in paddy soils across different rice growth periods and fertilization treatments. AOM activity ranged from 0.81 to 1.33 and 1.26 to 2.38 nmol of 13CO2 g-1 (dry soil) day-1 with HA and nitrate, respectively. No significant differences (p < 0.05) were observed between the AOM activity driven by HA and nitrate across the three fertilization treatments. According to AOM activity, the annual consumption of CH4 was estimated at approximately 0.49 ± 0.06 and 0.83 ± 0.19 Tg for AOM processes driven by HA and nitrate in Chinese paddy soils. Nitrate-driven AOM activity exhibited a positive (p < 0.05) correlation with the abundance of the ANME-2d mcrA gene but a negative (p < 0.05) correlation with the content of dissolved organic carbon. Intriguingly, HA-driven AOM activity was only correlated positively with the nitrate-driven AOM activity. Soil water content, soil organic carbon, nitrate and nitrite contents were significantly correlated with the relative abundance of methanogenic and methanotrophic archaea. These results identified the potential importance of HA and nitrate in driving AOM processes within paddy soils, providing a comprehensive understanding of the complex microbial processes regulating greenhouse gas emissions from paddy soils.

Role of n-DAMO in Mitigating Methane Emissions from Intertidal Wetlands Is Regulated by Saltmarsh Vegetations

Coastal wetlands are hotspots for methane (CH4) production, reducing their potential for global warming mitigation. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in bridging carbon and nitrogen cycles, contributing significantly to CH4 consumption. However, the role of n-DAMO in reducing CH4 emissions in coastal wetlands is poorly understood. Here, the ecological functions of the n-DAMO process in different saltmarsh vegetation habitats as well as bare mudflats were quantified, and the underlying microbial mechanisms were explored. Results showed that n-DAMO rates were significantly higher in vegetated habitats (Scirpus mariqueter and Spartina alterniflora) than those in bare mudflats (P < 0.05), leading to an enhanced contribution to CH4 consumption. Compared with other habitats, the contribution of n-DAMO to the total anaerobic CH4 oxidation was significantly lower in the Phragmites australis wetland (15.0%), where the anaerobic CH4 oxidation was primarily driven by ferric iron (Fe3+). Genetic and statistical analyses suggested that the different roles of n-DAMO in various saltmarsh wetlands may be related to divergent n-DAMO microbial communities as well as environmental parameters such as sediment pH and total organic carbon. This study provides an important scientific basis for a more accurate estimation of the role of coastal wetlands in mitigating climate change.

Anaerobic methanotrophy is stimulated by graphene oxide in a brackish urban canal sediment

Anthropogenic activities are influencing aquatic environments through increased chemical pollution and thus are greatly affecting the biogeochemical cycling of elements. This has increased greenhouse gas emissions, particularly methane, from lakes, wetlands, and canals. Most of the methane produced in anoxic sediments is converted into carbon dioxide by methanotrophs before it reaches the atmosphere. Anaerobic oxidation of methane requires an electron acceptor such as sulphate, nitrate, or metal oxides. Here, we explore the anaerobic methanotrophy in sediments of three urban canals in Amsterdam, covering a gradient from freshwater to brackish conditions. Biogeochemical analysis showed the presence of a shallow sulphate-methane transition zone in sediments of the most brackish canal, suggesting that sulphate could be a relevant electron acceptor for anaerobic methanotrophy in this setting. However, sediment incubations amended with sulphate or iron oxides (ferrihydrite) did not lead to detectable rates of methanotrophy. Despite the presence of known nitrate-dependent anaerobic methanotrophs (Methanoperedenaceae), no nitrate-driven methanotrophy was observed in any of the investigated sediments either. Interestingly, graphene oxide stimulated anaerobic methanotrophy in incubations of brackish canal sediment, possibly catalysed by anaerobic methanotrophs of the ANME-2a/b clade. We propose that natural organic matter serving as electron acceptor drives anaerobic methanotrophy in brackish sediments.

Evidence for Nitrous Oxide Emissions by Nitrite-Dependent Anaerobic Methane Oxidizing Bacteria

Nitrite-dependent anaerobic methane oxidizing (n-DAMO) bacteria generally convert nitrite to dinitrogen and bypass the nitrous oxide (N2O) formation step. However, N2O is often detected in n-DAMO bacteria dominated cultures and it remains an open question as to the microbial origin of N2O in these enrichments. Using a stable nitrite consuming microbial community enriched for n-DAMO bacteria, we demonstrated that N2O production was coupled to methane oxidation and the higher initial nitrite concentrations led to increased quantities of N2O being formed. Moreover, continuous exposure of the enrichment culture to about 5 mg of N L-1 nitrite resulted in constant N2O being produced (12.5% of nitrite was reduced to N2O). Metatranscriptomic analyses revealed that nitrite reductase (nirS) and nitric oxide reductase (norZ) transcripts from n-DAMO bacteria increased in response to nitrite exposure. No other bacteria significantly expressed nor genes under these conditions, suggesting n-DAMO bacteria are responsible for N2O being produced. In a 35-day bioreactor experiment, N2O produced by the n-DAMO bacteria accumulated when nitrite was in excess; this was found to be up to 3.2% of the nitrogen that resulted from nitrite removal. Together, these results suggested that excess nitrite is an important driver of N2O production by n-DAMO bacteria. To this end, proper monitoring and control of nitrite levels in wastewater treatment plants would be effective strategies for mitigating N2O emissions to the atmosphere.

Methanotrophic potential of Dutch canal wall biofilms is driven by Methylomonadaceae

Global urbanization of waterways over the past millennium has influenced microbial communities in these aquatic ecosystems. Increased nutrient inputs have turned most urban waters into net sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4). Here, canal walls of five Dutch cities were studied for their biofilm CH4 oxidation potential, alongside field observations of water chemistry, and CO2 and CH4 emissions. Three cities showed canal wall biofilms with relatively high biological CH4 oxidation potential up to 0.48 mmol gDW-1 d-1, whereas the other two cities showed no oxidation potential. Salinity was identified as the main driver of biofilm bacterial community composition. Crenothrix and Methyloglobulus methanotrophs were observed in CH4-oxidizing biofilms. We show that microbial oxidation in canal biofilms is widespread and is likely driven by the same taxa found across cities with distinctly different canal water chemistry. The oxidation potential of the biofilms was not correlated with the amount of CH4 emitted but was related to the presence or absence of methanotrophs in the biofilms. This was controlled by whether there was enough CH4 present to sustain a methanotrophic community. These results demonstrate that canal wall biofilms can directly contribute to the mitigation of greenhouse gases from urban canals.

Iron oxides act as an alternative electron acceptor for aerobic methanotrophs in anoxic lake sediments

Conventional aerobic CH₄-oxidizing bacteria (MOB) are frequently detected in anoxic environments, but their survival strategy and ecological contribution are still enigmatic. Here we explore the role of MOB in enrichment cultures under O₂ gradients and an iron-rich lake sediment in situ by combining microbiological and geochemical techniques. We found that enriched MOB consortium used ferric oxides as alternative electron acceptors for oxidizing CH₄ with the help of riboflavin when O₂ was unavailable. Within the MOB consortium, MOB transformed CH₄ to low molecular weight organic matter such as acetate for consortium bacteria as a carbon source, while the latter secrete riboflavin to facilitate extracellular electron transfer (EET). Iron reduction coupled to CH₄ oxidation mediated by the MOB consortium was also demonstrated in situ, reducing 40.3% of the CH₄ emission in the studied lake sediment. Our study indicates how MOBs survive under anoxia and expands the knowledge of this previously overlooked CH₄ sink in iron-rich sediments.

Spatio-temporal variations of activity of nitrate-driven anaerobic oxidation of methane and community structure of Candidatus Methanoperedens-like archaea in sediment of Wuxijiang river

Nitrate-driven anaerobic oxidation of methane (AOM), catalyzing by Candidatus Methanoperedens-like archaea, is a new addition in the global CH₄ cycle. This AOM process acts as a novel pathway for CH₄ emission reduction in freshwater aquatic ecosystems; however, its quantitative importance and regulatory factors in riverine ecosystems are nearly unknown. Here, we examined the spatio-temporal changes of the communities of Methanoperedens-like archaea and nitrate-driven AOM activity in sediment of Wuxijiang River, a mountainous river in China. These archaeal community composition varied significantly among reaches (upper, middle, and lower reaches) and between seasons (winter and summer), but their mcrA gene diversity showed no significant spatial or temporal variations. The copy numbers of Methanoperedens-like archaeal mcrA genes were 1.32 × 10⁵-2.47 × 10⁷ copies g^-1 (dry weight), and the activity of nitrate-driven AOM was 0.25-1.73 nmol CH₄ g^-1 (dry weight) d^-1, which could potentially reduce 10.3% of CH₄ emissions from rivers. Significant spatio-temporal variations of mcrA gene abundance and nitrate-driven AOM activity were found. Both the gene abundance and activity increased significantly from upper to lower reaches in both seasons, and were significantly higher in sediment collected in summer than in winter. In addition, the variations of Methanoperedens-like archaeal communities and nitrate-driven AOM activity were largely impacted by the sediment temperature, NH₄⁺ and organic carbon contents. Taken together, both time and space scales need to be considered for better evaluating the quantitative importance of nitrate-driven AOM in reducing CH₄ emissions from riverine ecosystems.

Water level of inland saline wetlands with implications for CO2 and CH4 fluxes during the autumn freeze-thaw period in Northeast China

Zhalong wetland is the largest inland saline wetland in Asia and susceptible to imbalance and frequent flooding during the freeze-thaw period. Changes in water level and temperature can alter the rate of greenhouse gas release from wetlands and have the potential to alter Earth's carbon budget. However, there are few reports on how water level, temperature, and their interactions affect greenhouse gas flux in inland saline wetland during the freeze-thaw period. This study revealed the characteristics of CO₂ and CH₄ fluxes in Zhalong saline wetlands at different water levels during the autumn freeze-thaw period and clarifies the response of CO₂ and CH₄ fluxes to water levels. The significance analysis of cumulative CO₂ fluxes at different water levels showed that water levels did not have a significant effect on cumulative CO₂ release fluxes from wetlands. Water levels, temperature, soil moisture content, soil nitrate, and ammonium nitrogen content and organic carbon content could explain 24.5-98.9% of CO₂ and CH₄ flux variation. There were significant differences in the average and cumulative CH₄ fluxes at different water levels. The higher the water levels, the higher the CH₄ fluxes. In short, water level had a significant effect on wetland methane fluxes, but not on carbon dioxide fluxes.

Role and regulation of anaerobic methane oxidation catalyzed by NC10 bacteria and ANME-2d archaea in various ecosystems

Freshwater wetlands, paddy fields, inland aquatic ecosystems and coastal wetlands are recognized as important sources of atmospheric methane (CH₄). Currently, increasing evidence shows the potential importance of the anaerobic oxidation of methane (AOM) mediated by NC10 bacteria and a novel cluster of anaerobic methanotrophic archaea (ANME)-ANME-2d in mitigating CH₄ emissions from different ecosystems. To better understand the role of NC10 bacteria and ANME-2d archaea in CH₄ emission reduction, the current review systematically summarizes different AOM processes and the functional microorganisms involved in freshwater wetlands, paddy fields, inland aquatic ecosystems and coastal wetlands. NC10 bacteria are widely present in these ecosystems, and the nitrite-dependent AOM is identified as an important CH₄ sink and induces nitrogen loss. Nitrite- and nitrate-dependent AOM co-occur in the environment, and they are mainly affected by soil/sediment inorganic nitrogen and organic carbon contents. Furthermore, salinity is another key factor regulating the two AOM processes in coastal wetlands. In addition, ANME-2d archaea have the great potential to couple AOM to the reduction of iron (III), manganese (IV), sulfate, and even humics in different ecosystems. However, the study on the environmental distribution of ANME-2d archaea and their role in CH₄ mitigation in environments is insufficient. In this study, we propose several directions for future research on the different AOM processes and respective functional microorganisms.

Detection and Quantification of Candidatus Methanoperedens-Like Archaea in Freshwater Wetland Soils

Candidatus Methanoperedens-like archaea, which can use multiple electron acceptors (nitrate, iron, manganese, and sulfate) for anaerobic methane oxidation, could play an important role in reducing methane emissions from freshwater wetlands. Currently, very little is known about the distribution and community composition of Methanoperedens-like archaea in freshwater wetlands, particularly based on their alpha subunit of methyl-coenzyme M reductase (mcrA) genes. Here, the community composition, diversity, and abundance of Methanoperedens-like archaea were investigated in a freshwater wetland through high-throughput sequencing and quantitative PCR on their mcrA genes. A large number of Methanoperedens-like mcrA gene sequences (119,250) were recovered, and a total of 31 operational taxonomic units (OTUs) were generated based on 95% sequence similarity cut-off. The majority of Methanoperedens-like sequences can be grouped into three distinct clusters that were closely associated with the known Methanoperedens species which can couple anaerobic methane oxidation to nitrate or iron reduction. The community composition of Methanoperedens-like archaea differed significantly among different sampling sites, and their mcrA gene abundance was 1.49 × 10⁶ ~ 4.62 × 10⁶ copies g^-1 dry soil in the examined wetland. In addition, the community composition of Methanoperedens-like archaea was significantly affected by the soil water content, and the archaeal abundance was significantly positively correlated with the water content. Our results suggest that the mcrA gene is a good biomarker for detection and quantification of Methanoperedens-like archaea, and provide new insights into the distribution and environmental regulation of these archaea in freshwater wetlands.

Effects of periodic drying-wetting on microbial dynamics and activity of nitrite/nitrate-dependent anaerobic methane oxidizers in intertidal wetland sediments

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays an important role in methane (CH₄) consumption in intertidal wetlands. However, little is known about the responses of n-DAMO in intertidal wetlands to periodic drying-wetting caused by tidal cycling. Here, comparative experiments (waterlogged, desiccated, reflooded) with the Yangtze estuarine intertidal sediments were performed to examine the effects of periodic tidal changes on n-DAMO microbial communities, abundances, and potential activities. Functional gene sequencing indicated the coexistence of n-DAMO bacteria and archaea in the tide-fluctuating environments and generally higher biodiversity under reflooded conditions than consecutive inundation or emersion. The n-DAMO microbial abundance and associated activity varied significantly during alternative exposure and inundation, with higher abundance and activity under the waterlogged than desiccated conditions. Reflooding of intertidal wetlands might intensify n-DAMO activities, indicating the resilience of n-DAMO microbial metabolisms to the wetting-drying events. Structural equation modeling and correlation analysis showed that n-DAMO activity was highly related to n-DAMO microbial abundance and substrate availability under inundation, whereas salt accumulation in sediment was the primary factor restraining n-DAMO activity under the desiccation. Overall, this study reveals tidal-induced shifts of n-DAMO activity and associated contribution to mitigating CH₄, which may help accurately project CH₄ emission from intertidal wetlands under different tidal scenarios.

Soil nitrogen substances and denitrifying communities regulate the anaerobic oxidation of methane in wetlands of Yellow River Delta, China

Anaerobic oxidation of methane (AOM) in wetland soils is widely recognized as a key sink for the greenhouse gas methane (CH₄). The occurrence of this reaction is influenced by several factors, but the exact process and related mechanism of this reaction remain unclear, due to the complex interactions between multiple influencing factors in nature. Therefore, we investigated how environmental and microbial factors affect AOM in wetlands using laboratory incubation methods combined with molecular biology techniques. The results showed that wetland AOM was associated with a variety of environmental factors and microbial factors. The environmental factors include such as vegetation, depth, hydrogen ion concentration (pH), oxidation-reduction potential (ORP), electrical conductivity (EC), total nitrogen (TN), nitrate (NO₃^-), sulfate (SO₄^2-), and nitrous oxide (N₂O) flux, among them, soil N substances (TN, NO₃^-, N₂O) have essential regulatory roles in the AOM process, while NO₃^- and N₂O may be the key electron acceptors driving the AOM process under the coexistence of multiple electron acceptors. Moreover, denitrification communities (narG, nirS, nirK, nosZI, nosZII) and anaerobic methanotrophic (ANME-2d) were identified as important functional microorganisms affecting the AOM process, which is largely regulated by the former. In the environmental context of growing global anthropogenic N inputs to wetlands, these findings imply that N cycle-mediated AOM processes are a more important CH₄ sink for controlling global climate change. This studying contributes to the knowledge and prediction of wetland CH₄ biogeochemical cycling and provides a microbial ecology viewpoint on the AOM response to global environmental change.

Spatial variations of activity and community structure of nitrite-dependent anaerobic methanotrophs in river sediment

Rivers are an important site for methane emissions and reactive nitrogen removal. The process of nitrite-dependent anaerobic methane oxidation (n-damo) links the global carbon cycle and the nitrogen cycle, but its role in methane mitigation and nitrogen removal in rivers is poorly known. In the present study, we investigated the activity, abundance, and community composition of n-damo bacteria in sediment of the upper, middle, and lower reaches of Wuxijiang River (Zhejiang Province, China). The ¹³CH₄ stable isotope experiments showed that the methane oxidation activity of n-damo was 0.11-1.88 nmol CO₂ g^-1 (dry sediment) d^-1, and the activity measured from the middle reaches was significantly higher than that from the remaining regions. It was estimated that 3.27 g CH₄ m^-2 year^-1 and 8.72 g N m^-2 year^-1 could be consumed via n-damo. Quantitative PCR confirmed the presence of n-damo bacteria, and their 16S rRNA gene abundance varied between 5.45 × 10⁵ and 5.86 × 10⁶ copies g^-1 dry sediment. Similarly, the abundance of n-damo bacteria was significantly higher in the middle reaches. High-throughput sequencing showed a high n-damo bacterial diversity, with totally 152 operational taxonomic units being detected at 97 % sequence similarity cut-off. In addition, the n-damo bacterial community composition also varied spatially. The inorganic nitrogen (NH₄⁺, NO₂^-, NO₃^-) level was found to be the key environmental factor controlling the n-damo activity and bacterial community composition. Overall, our results showed the spatial variations and environmental regulation of the activity and community structure of n-damo bacteria in river sediment, which expanded our understanding of the quantitative importance of n-damo in both methane oxidation and reactive nitrogen removal in riverine systems.

Characterization of anaerobic oxidation of methane and microbial community in landfills with aeration

Landfills are the third largest source of anthropogenic CH₄ emissions. Anaerobic oxidation of methane (AOM) activity and communities of methane-oxidizing bacteria were investigated in three informal landfills in this study, namely, BJ, CH and SZ landfills, among which BJ and CH represent traditional anaerobic landfills, while the SZ landfill was subjected to aeration to accelerate waste stabilization. The AOM rates of the investigated landfilled wastes ranged from 3.66 to 23.91 nmol g^-1 h^-1. Among the three landfills, the AOM rate was highest in the SZ-1-Top sample, which was closest to the aeration pipe. Among the possible electron acceptors for AOM, including NO₃^-, NO₂^-, SO₄^2- and Fe³⁺, the NO₂^--N content was the only variable that was positively correlated with the AOM rate. Compared with α-Proteobacteria methanotrophs, γ-Proteobacteria methanotrophs were more abundant in the landfilled waste, especially Methylobacter, which was detected in nearly all samples. Members of the family Methylomirabilaceae, including Candidatus Methylomirabilis, were also detected in the SZ-1 and SZ-2-Bot samples. The relative abundance of the main methanotrophs in the families Methylomonadaceae, Methylococcaceae, Rokubacteriales and Methylomirabilaceae, the genus Methylocystis and the phylum NC10 were all positive correlations with the contents of NO₂^--N in the landfilled waste samples. Additionally, significantly positive correlations were observed between the AOM rates and the relative abundance of the main methanotrophs except for the family Methylococcaceae. This indicated that aeration could enhance the conversion of nitrogen compounds in the landfilled waste, in which the high contents of NO₂^--N could stimulate the growth of methanotrophs and increase AOM rate. These findings are helpful for understanding the mechanisms of CH₄ oxidation in landfills and for taking effective measures to mitigate CH₄ emissions from landfills.

Potential role of nitrite-dependent anaerobic methane oxidation in methane consumption and nitrogen removal in Chinese paddy fields

Nitrite-dependent anaerobic methane oxidation (n-damo), catalyzed by bacteria closely related to Candidatus Methylomirabilis oxyfera, links the global carbon and nitrogen cycles. Currently, the contribution of n-damo in controlling methane emissions and nitrogen removal, and the key regulatory factors of this process in Chinese paddy fields are poorly known. Here, soil samples from 20 paddy fields located in different climate zones across China were collected to examine the n-damo activity and bacterial communities. The n-damo activity and bacterial abundance varied from 1.05 to 5.97 nmol CH₄ g^-1 (dry soil) d^-1 and 2.59 × 10⁵ to 2.50 × 10⁷ copies g^-1 dry soil, respectively. Based on the n-damo activity, it was estimated that approximately 0.91 Tg CH₄ and 2.17 Tg N could be consumed annually via n-damo in Chinese paddy soils. The spatial variations in n-damo activity and community structure of n-damo bacteria were significantly (p < 0.05) affected by the soil ammonium content, labile organic carbon content and pH. Furthermore, significant differences in n-damo activity, bacterial abundance and community composition were observed among different climate zones. The n-damo activity was found to be positively correlated with the mean annual air temperature. Taken together, our results demonstrated the potential importance of n-damo in both methane consumption and nitrogen removal in Chinese paddy soils, and this process was regulated by local soil and climatic factors.

Quinolone antibiotics enhance denitrifying anaerobic methane oxidation in Wetland sediments: Counterintuitive results

Denitrifying anaerobic methane oxidation (DAMO) plays an important role in the element cycle of wetlands. In recent years, the content of antibiotics in wetlands has gradually increased due to human activities. However, the impact of antibiotics on the ecological function of DAMO remains unclear. Here we studied the influence of three high-content quinolone antibiotics (QNs) on DAMO in the sediments of the Baiyangdian Wetland. The results show that QNs can significantly promote the potential DAMO rates. Moreover, the enhancement of potential DAMO rates is positively correlated with the dosage of QNs. This promotion effect of QNs on nitrate-DAMO can be attributed to the hormesis phenomenon or their inhibition of substrate competitors. As antibacterial agents, QNs inhibit nitrite-DAMO conducted by bacteria, but greatly promote nitrate-DAMO conducted by archaea. These results suggest that the short-term effect of QNs on DAMO in wetlands is promotion rather than inhibition.

Response of potential activity, abundance and community composition of nitrite-dependent anaerobic methanotrophs to long-term fertilization in paddy soils

The process of nitrite-dependent anaerobic methane oxidation (n-damo) catalysed by Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria is a novel pathway in regulating methane (CH₄ ) emissions from paddy fields. Nitrogen fertilization is essential to improve rice yields and soil fertility; however, its effect on the n-damo process is largely unknown. Here, the potential n-damo activity, abundance and community composition of M. oxyfera-like bacteria were investigated in paddy fields under three long-term (32 years) fertilization treatments, i.e. unfertilized control (CK), chemical fertilization (NPK) and straw incorporation with chemical fertilization (SNPK). Relative to the CK, both NPK and SNPK treatments significantly (p < 0.05) increased the potential n-damo activity (88%-110%) and the abundance (52%-105%) of M. oxyfera-like bacteria. The variation of soil organic carbon (OrgC) content and inorganic nitrogen content caused by the input of chemical fertilizers and straw returning were identified as the key factors affecting the potential n-damo activity and the abundance of M. oxyfera-like bacteria. However, the community composition and diversity of M. oxyfera-like bacteria did not change significantly by the input of fertilizers. Overall, our results provide the first evidence that long-term fertilization greatly stimulates the n-damo process, indicating its active role in controlling CH₄ emissions from paddy fields.

Response of the Anaerobic Methanotrophic Archaeon Candidatus "Methanoperedens nitroreducens" to the Long-Term Ferrihydrite Amendment

Anaerobic methanotrophic (ANME) archaea can drive anaerobic oxidation of methane (AOM) using solid iron or manganese oxides as the electron acceptors, hypothetically via direct extracellular electron transfer (EET). This study investigated the response of Candidatus "Methanoperedens nitroreducens TS" (type strain), an ANME archaeon previously characterized to perform nitrate-dependent AOM, to an Fe(III)-amended condition over a prolonged period. Simultaneous consumption of methane and production of dissolved Fe(II) were observed for more than 500 days in the presence of Ca. "M. nitroreducens TS," indicating that this archaeon can carry out Fe(III)-dependent AOM for a long period. Ca. "M. nitroreducens TS" possesses multiple multiheme c-type cytochromes (MHCs), suggesting that it may have the capability to reduce Fe(III) via EET. Intriguingly, most of these MHCs are orthologous to those identified in Candidatus "Methanoperedens ferrireducens," an Fe(III)-reducing ANME archaeon. In contrast, the population of Ca. "M. nitroreducens TS" declined and was eventually replaced by Ca. "M. ferrireducens," implying niche differentiation between these two ANME archaea in the environment.

NO3- is an important driver of nitrite-dependent anaerobic methane oxidation bacteria and CH4 fluxes in the reservoir riparian zone

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is an important biological process that combines microbial nitrogen and carbon cycling and is mainly carried out by nitrite-dependent anaerobic methane-oxidizing bacteria. The discovery of this microbial process has changed the conventional view of methane oxidation and nitrogen loss. In this study, the abundance, diversity, and community structure of N-DAMO bacteria were investigated based on high-throughput sequencing and fluorescence quantitative PCR measurements. We examined environmental factors driving the variations of CH₄ fluxes and N-DAMO bacterial using correlation analysis and redundancy analysis. We found low CH₄ fluxes and abundant N-DAMO bacteria in the riparian zone. After decomposing the effects of single variables and exploring them, NO₃^- was the only significant factor that significantly correlated with the abundance and richness of the N-DAMO community and gas fluxes (p < 0.05). Under the influence of three different land use types, the increase in NO₃^- (grassland vs. woodland and sparse woods, + 132.81% and + 106.25%) caused structural changes in the composition of the N-DAMO bacterial community, increasing its abundance (- 9.58% and + 21.19%), thus promoting the oxidation of CH₄ and reduced CH₄ emissions (+ 4.78% and + 35.63%) from the riparian zone. Appropriate NO₃^- input helps maintain the existing low methane emission fluxes in the riparian zone of the reservoir.

Shotgun Metagenomics of Deep Forest Soil Layers Show Evidence of Altered Microbial Genetic Potential for Biogeochemical Cycling

Soil microorganisms such as Bacteria and Archaea play important roles in the biogeochemical cycling of soil nutrients, because they act as decomposers or are mutualistic or antagonistic symbionts, thereby influencing plant growth and health. In the present study, we investigated the vertical distribution of soil metagenomes to a depth of 1.5 m in Swiss forests of European beech and oak species on calcareous bedrock. We explored the functional genetic potential of soil microorganisms with the aim to disentangle the effects of tree genus and soil depth on the genetic repertoire, and to gain insight into the microbial C and N cycling. The relative abundance of reads assigned to taxa at the domain level indicated a 5-10 times greater abundance of Archaea in the deep soil, while Bacteria showed no change with soil depth. In the deep soil there was an overrepresentation of genes for carbohydrate-active enzymes, which are involved in the catalyzation of the transfer of oligosaccharides, as well as in the binding of carbohydrates such as chitin or cellulose. In addition, N-cycling genes (NCyc) involved in the degradation and synthesis of N compounds, in nitrification and denitrification, and in nitrate reduction were overrepresented in the deep soil. Consequently, our results indicate that N-transformation in the deep soil is affected by soil depth and that N is used not only for assimilation but also for energy conservation, thus indicating conditions of low oxygen in the deep soil. Using shotgun metagenomics, our study provides initial findings on soil microorganisms and their functional genetic potential, and how this may change depending on soil properties, which shift with increasing soil depth. Thus, our data provide novel, deeper insight into the "dark matter" of the soil.

Microbial dynamics and activity of denitrifying anaerobic methane oxidizers in China's estuarine and coastal wetlands

Estuarine and coastal wetlands, which act as large sources of methane (CH₄) and undergo substantial loading of anthropogenic nitrogen (N), provide ideal conditions for denitrifying anaerobic methane oxidation (DAMO) to occur. Yet the microbial mechanisms governing DAMO and the main driving factors in estuarine and coastal ecosystems remain unclear. This study investigated the spatiotemporal distribution and associated activity of DAMO microorganisms along a wide swath of China's coastline (latitudinal range: 22-41°N) using molecular assays and isotope tracing techniques. We uncovered significant spatial and seasonal variation in DAMO bacterial community structure, whereas DAMO archaeal community structure exhibited no seasonal differences. The abundance of DAMO bacterial pmoA gene (2.2 × 10⁵-1.0 × 10⁷ copies g^-1) was almost one order of magnitude higher than that of DAMO archaeal mcrA gene (8.7 × 10⁴ -1.8 × 10⁶ copies g^-1). A significant positive correlation between pmoA and mcrA gene abundances (p < 0.01) was observed, indicating that DAMO bacteria and archaea may cooperate closely and thus complete nitrate elimination. Potential DAMO rates, in the range of 0.09-23.4 nmol ¹³CO₂ g^-1 day^-1 for nitrite-DAMO and 0.03-43.7 nmol ¹³CO₂ g^-1 day^-1 for nitrate-DAMO, tended to be greater in the relatively warmer low-latitudes. Potential DAMO rates were weakly positively correlated with gene abundances, suggesting that DAMO microbial activity could not be predicted directly by gene abundance alone. The heterogeneous variability of DAMO was shaped by interactions among key environmental characteristics (sediment texture, N availability, TOC, Fe³⁺, salinity of water, and temperature). On a broader continental scale, potential N removal rates of 0.1-11.2 g N m^-2 yr^-1 were estimated via nitrite-DAMO activity in China's coastal wetlands. Overall, our results highlight the widespread distribution of DAMO microbes and their potential role in eliminating excess N inputs and reducing CH₄ emissions in estuarine and coastal ecosystems, which could help mitigate global warming.

Hydrological properties predict the composition of microbial communities cycling methane and nitrogen in rivers

Sediment microbial communities drive the biogeochemical cycles that make rivers globally important sources and sinks of carbon (C) and nitrogen (N). The structure of these communities is strongly determined by the local physico-chemical environment. However, we currently lack an understanding of the factors that determine microbial community structures at the catchment scale. Here, we show that the contribution of groundwater to total river flow (quantified as base flow index; BFI) predicts the structure and diversity of the different microbial functional groups that cycle N and C across nine UK rivers, spanning a geological BFI gradient from 0.23 (clay sediment) to 0.95 (chalk gravel sediment). Furthermore, the GC-content (percentage of guanine-cytosine bases in a DNA sequence) and codon-usage bias of ammonia monooxygenase DNA sequences, and the hydrophobicity and net-charge of the corresponding amino acid sequences, were all strongly correlated with BFI, likely reflecting physiological adaptations to different riverbed sediment structure along the BFI gradient. Our results offer an opportunity to overcome the "paradox of scales" that has seen microbial ecologists focus on small- rather than large-scale environmental variables, enabling us to scale-up our understanding of microbial biogeochemistry to the catchment and beyond.

Metabolic flexibility of aerobic methanotrophs under anoxic conditions in Arctic lake sediments

Methane (CH₄) emissions from Arctic lakes are a large and growing source of greenhouse gas to the atmosphere with critical implications for global climate. Because Arctic lakes are ice covered for much of the year, understanding the metabolic flexibility of methanotrophs under anoxic conditions would aid in characterizing the mechanisms responsible for limiting CH₄ emissions from high-latitude regions. Using sediments from an active CH₄ seep in Lake Qalluuraq, Alaska, we conducted DNA-based stable isotope probing (SIP) in anoxic mesocosms and found that aerobic Gammaproteobacterial methanotrophs dominated in assimilating CH₄. Aerobic methanotrophs were also detected down to 70 cm deep in sediments at the seep site, where anoxic conditions persist. Metagenomic analyses of the heavy DNA from ¹³CH₄-SIP incubations showed that these aerobic methanotrophs had the capacity to generate intermediates such as methanol, formaldehyde, and formate from CH₄ oxidation and to oxidize formaldehyde in the tetrahydromethanopterin (H₄MPT)-dependent pathway under anoxic conditions. The high levels of Fe present in sediments, combined with Fe and CH₄ profiles in the persistent CH₄ seep site, suggested that oxidation of CH₄, or, more specifically, its intermediates such as methanol and formaldehyde might be coupled to iron reduction. Aerobic methanotrophs also possessed genes associated with nitrogen and hydrogen metabolism, which might provide potentially alternative energy conservation options under anoxic conditions. These results expand the known metabolic spectrum of aerobic methanotrophs under anoxic conditions and necessitate the re-assessment of the mechanisms underlying CH₄ oxidation in the Arctic, especially under lakes that experience extended O₂ limitations during ice cover.

Response of nitrite-dependent anaerobic methanotrophs to elevated atmospheric CO2 concentration in paddy fields

Nitrite-dependent anaerobic methane oxidation (n-damo) catalyzed by Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria is a new pathway for the regulation of methane emissions from paddy fields. Elevated atmospheric CO₂ concentrations (e[CO₂]) can indirectly affect the structure and function of microbial communities. However, the response of M. oxyfera-like bacteria to e[CO₂] is currently unknown. Here, we investigated the effect of e[CO₂] (ambient CO₂ + 200 ppm) on community composition, abundance, and activity of M. oxyfera-like bacteria at different depths (0-5, 5-10, and 10-20 cm) in paddy fields across multiple rice growth stages (tillering, jointing, and flowering). High-throughput sequencing showed that e[CO₂] had no significant effect on the community composition of M. oxyfera-like bacteria. However, quantitative PCR suggested that the 16S rRNA gene abundance of M. oxyfera-like bacteria increased significantly in soil under e[CO₂], particularly at the tillering stage. Furthermore, ¹³CH₄ tracer experiments showed potential n-damo activity of 0.31-8.91 nmol CO₂ g^-1 (dry soil) d^-1. E[CO₂] significantly stimulated n-damo activity, especially at the jointing and flowering stages. The n-damo activity and abundance of M. oxyfera-like bacteria increased by an average of 90.9% and 50.0%, respectively, under e[CO₂]. Correlation analysis showed that the increase in soil dissolved organic carbon content caused by e[CO₂] had significant effects on the activity and abundance of M. oxyfera-like bacteria. Overall, this study provides the first evidence for a positive response of M. oxyfera-like bacteria to e[CO₂], which may help reduce methane emissions from paddy fields under future climate change conditions.

Amsterdam urban canals contain novel niches for methane-cycling microorganisms

Urbanised environments have been identified as hotspots of anthropogenic methane emissions. Especially urban aquatic ecosystems are increasingly recognised as important sources of methane. However, the microbiology behind these emissions remains unexplored. Here, we applied microcosm incubations and molecular analyses to investigate the methane‐cycling community of the Amsterdam canal system in the Netherlands. The sediment methanogenic communities were dominated by Methanoregulaceae and Methanosaetaceae, with co‐occurring methanotrophic Methanoperedenaceae and Methylomirabilaceae indicating the potential for anaerobic methane oxidation. Methane was readily produced after substrate amendment, suggesting an active but substrate‐limited methanogenic community. Bacterial 16S rRNA gene amplicon sequencing of the sediment revealed a high relative abundance of Thermodesulfovibrionia. Canal wall biofilms showed the highest initial methanotrophic potential under oxic conditions compared to the sediment. During prolonged incubations the maximum methanotrophic rate increased to 8.08 mmol g_DW⁻¹ d⁻¹ that was concomitant with an enrichment of Methylomonadaceae bacteria. Metagenomic analysis of the canal wall biofilm lead to the recovery of a single methanotroph metagenome‐assembled genome. Taxonomic analysis showed that this methanotroph belongs to the genus Methyloglobulus. Our results underline the importance of previously unidentified and specialised environmental niches at the nexus of the natural and human‐impacted carbon cycle.

Anaerobic oxidation of methane mediated by microbial extracellular respiration

Anaerobic oxidation of methane (AOM) can be microbially mediated by the reduction of different terminal electron acceptors. AOM coupled to reduction of sulfate, manganese/iron oxides, humic substances, selenate, arsenic and other artificial extracellular electron acceptors are recognized as processes associated with microbial extracellular respiration. In these processes, methane-oxidizing archaea transfer electrons to external electron acceptors or to interdependent microbial species, which are mechanistically dependent on versatile extracellular electron transfer (EET) pathways. This review compiles recent progress in the research of electromicrobiology of AOM based on the catalogue of different electron acceptors. Naturally distributed and artificially constructed EET-mediated AOM is summarized, with the discussion of their environmental importance and application potentials. The diversity of responsible microorganisms involved in EET-mediated AOM is discussed with both methane-oxidizing archaea and their putative bacterial partners. More importantly, the review highlights progress and deficiencies in our understanding of EET pathways in EET-mediated AOM, raising open research questions for future research.

The anaerobic oxidation of methane in paddy soil by ferric iron and nitrate, and the microbial communities involved

The anaerobic oxidation of methane (AOM) mediated by microorganisms is a key process in the reduction of methane emissions, and AOM-coupled electron acceptors have been shown to regulate methane emissions into the atmosphere in marine systems. Paddy fields are a significant source of methane and account for 20% of global methane emissions, but the effect of electron acceptors on the methane emission process in flooded paddy fields has been poorly characterized. This study aimed to determine whether the electron acceptors ferric iron and nitrate, and biochar, acting as an electron shuttle, can regulate the AOM process in paddy soil, with or without interaction between biochar and these two electron acceptors. We also aimed to characterize which microorganisms are actively involved. Here, we added ¹³C-labeled CH₄ (¹³CH₄) into anaerobic microcosms to evaluate the role of electron acceptors by measuring the methane oxidation rate and the enrichment of ¹³C-labeled CO₂ (¹³CO₂). We then combined DNA-stable isotope probing with amplicon sequencing to study the active microorganisms. We found for the first time that, in addition to nitrate, ferric iron can also effectively promote AOM in paddy soil. However, there was no significant effect of biochar. Ferric iron-dependent AOM was mainly carried out by iron-reducing bacteria (Geobacter, Ammoniphilus and Clostridium), and nitrate-dependent AOM was mainly by nitrate-reducing bacteria (Rhodanobacter, Paenibacillus and Planococcus). Our results demonstrate that the AOM process, regulated by the electron acceptors ferric iron and nitrate, can alleviate methane emission from paddy soil. The potentially active microorganisms related to electron acceptor reduction may be crucial for this methane sink and deserve further research.

Microbial transformation of biogenic and abiogenic Fe minerals followed by in-situ incubations in an As-contaminated vs. non-contaminated aquifer

Fe(III) minerals play a crucial role for arsenic (As) mobility in aquifers as they usually represent the main As-bearing phases. Microbial reductive dissolution of As-bearing Fe(III) minerals is responsible for the release of As and the resulting groundwater contamination in many sites worldwide. So far, in most studies mainly abiogenic iron minerals have been considered. Yet, biogenic minerals that possess different properties to their abiogenic counterparts are also present in the environment. In some environments they dominate the iron mineral inventory but so far, it is unclear what this means for the As mobility. We, therefore, performed an in-situ aquifer Fe(III) minerals exposure experiment i) to evaluate how different biogenic and abiogenic Fe(III) minerals are transformed in a strongly reducing, As-contaminated aquifer (25 m) compared to As-free moderately reducing aquifer (32 m) and ii) to assess which microbial taxa are involved in these Fe(III) minerals transformations. We found that higher numbers of bacteria and archaea were associated with the minerals incubated in the As-contaminated compared to the non-contaminated aquifer and that all Fe(III) minerals were mainly colonized by Fe(III)-reducing bacteria, with Geobacter being the most abundant taxon. Additionally, fermenting microorganisms were abundant on minerals incubated in the As-contaminated aquifer, while methanotrophs were identified on the minerals incubated in the As-free moderately reducing aquifer, implying involvement of these microorganisms in Fe(III) reduction. We observed that biogenic Fe(III) minerals generally tend to become more reduced and when incubated in the As-contaminated aquifer sorbed more As than the abiogenic ones. Most of abiogenic and biogenic Fe(III) minerals were transformed into magnetite while biogenic more crystalline mixed phases were not subjected to visible transformation. This in-situ Fe(III) minerals incubation approach shows that biogenic minerals are more prone to be colonized by (Fe(III)-reducing) microorganisms and bind more As, although ultimately produce similar minerals during Fe(III) reduction.

Methanotrophs: Discoveries, Environmental Relevance, and a Perspective on Current and Future Applications

Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, co-existence, interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.