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Seasonal floodplains in the Amazon basin are important sources of methane (CH4), while upland forests are known for their sink capacity. Climate change effects, including shifts in rainfall patterns and rising temperatures, may alter the functionality of soil microbial communities, leading to uncertain changes in CH4 cycling dynamics. To investigate the microbial feedback under climate change scenarios, we performed a microcosm experiment using soils from two floodplains (i.e., Amazonas and Tapajós rivers) and one upland forest. We employed a two-factorial experimental design comprising flooding (with non-flooded control) and temperature (at 27 °C and 30 °C, representing a 3 °C increase) as variables. We assessed prokaryotic community dynamics over 30 days using 16S rRNA gene sequencing and qPCR. These data were integrated with chemical properties, CH4 fluxes, and isotopic values and signatures. In the floodplains, temperature changes did not significantly affect the overall microbial composition and CH4 fluxes. CH4 emissions and uptake in response to flooding and non-flooding conditions, respectively, were observed in the floodplain soils. By contrast, in the upland forest, the higher temperature caused a sink-to-source shift under flooding conditions and reduced CH4 sink capability under dry conditions. The upland soil microbial communities also changed in response to increased temperature, with a higher percentage of specialist microbes observed. Floodplains showed higher total and relative abundances of methanogenic and methanotrophic microbes compared to forest soils. Isotopic data from some flooded samples from the Amazonas river floodplain indicated CH4 oxidation metabolism. This floodplain also showed a high relative abundance of aerobic and anaerobic CH4 oxidizing Bacteria and Archaea. Taken together, our data indicate that CH4 cycle dynamics and microbial communities in Amazonian floodplain and upland forest soils may respond differently to climate change effects. We also highlight the potential role of CH4 oxidation pathways in mitigating CH4 emissions in Amazonian floodplains.

Methane is a powerful greenhouse gas, more potent than carbon dioxide, and emitted from a variety of natural sources including wetlands, permafrost, mammalian guts and termites. As increases in global temperatures continue to break records, quantifying the magnitudes of key methane sources has never been more pertinent. Over the last 40 years, the contribution of termites to the global methane budget has been subject to much debate. The most recent estimates of termite emissions range between 9 and 15 Tg CH4 year-1, approximately 4% of emissions from natural sources (excluding wetlands). However, we argue that the current approach for estimating termite contributions to the global methane budget is flawed. Key parameters, namely termite methane emissions from soil, deadwood, living tree stems, epigeal mounds and arboreal nests, are largely ignored in global estimates. This omission occurs because data are lacking and research objectives, crucially, neglect variation in termite ecology. Furthermore, inconsistencies in data collection methods prohibit the pooling of data required to compute global estimates. Here, we summarise the advances made over the last 40 years and illustrate how different aspects of termite ecology can influence the termite contribution to global methane emissions. Additionally, we highlight technological advances that may help researchers investigate termite methane emissions on a larger scale. Finally, we consider dynamic feedback mechanisms of climate warming and land-use change on termite methane emissions. We conclude that ultimately the global contribution of termites to atmospheric methane remains unknown and thus present an alternative framework for estimating their emissions. To significantly improve estimates, we outline outstanding questions to guide future research efforts.

Clumped isotopes of methane (CH 4), specifically Δ 13 CH 3 D and Δ 12 CH 2 D 2 , provide additional information to constrain its sources and sink processes. These isotopes complement interpretations of CH 4 provenance based on bulk isotopes. However, interpreting the origin of CH 4 using isotopes becomes challenging when the isotopic signature is altered by post-generation processes. In this study, we measured, for the first time, the bulk and clumped isotopic composition of sub-glacial CH 4 samples. These samples were collected from the air-filled headspace of the glacier portal (ice cave) at the edge of the Isunnguata Sermia glacier (ISG), located at the western margin of the Greenland ice sheet (GrIS). Our goal was to identify the processes underlying the sub-glacial production and potential processing of CH 4. The Δ 13 CH 3 D and Δ 12 CH 2 D 2 values of the samples measured in this study are 3.7 ± 0.3‰ and 39.7 ± 2.0‰, respectively (95% confidence interval). The Δ 12 CH 2 D 2 values are close to those of atmospheric CH 4. The elevated Δ 12 CH 2 D 2 values can be attributed to the alteration of the source's isotope signal by aerobic oxidation. This conclusion is supported by previous studies at this site, which reported the presence of methanotrophic bacteria and dissolved oxygen close to saturation in the meltwater. Our results confirm that the correlation between Δ 13 CH 3 D and Δ 12 CH 2 D 2 is a useful tool for deciphering oxidation pathways. Our results support the inference that aerobic CH 4 oxidation can strongly modify the Δ 12 CH 2 D 2 isotope signal, which must be considered when determining the source signatures of environmental samples. [ABSTRACT FROM AUTHOR]

Recent studies have unveiled the deep sea as a rich biosphere, populated by species descended from shallow-water ancestors post-mass extinctions. Research on genomic evolution and microbial symbiosis has shed light on how these species thrive in extreme deep-sea conditions. However, early adaptation stages, particularly the roles of conserved genes and symbiotic microbes, remain inadequately understood. This study examined transcriptomic and microbiome changes in shallow-water mussels Mytilus galloprovincialis exposed to deep-sea conditions at the Site-F cold seep in the South China Sea. Results reveal complex gene expression adjustments in stress response, immune defense, homeostasis, and energy metabolism pathways during adaptation. After 10 days of deep-sea exposure, shallow-water mussels and their microbial communities closely resembled those of native deep-sea mussels, demonstrating host and microbiome convergence in response to adaptive shifts. Notably, methanotrophic bacteria, key symbionts in native deep-sea mussels, emerged as a dominant group in the exposed mussels. Host genes involved in immune recognition and endocytosis correlated significantly with the abundance of these bacteria. Overall, our analyses provide insights into adaptive transcriptional regulation and microbiome dynamics of mussels in deep-sea environments, highlighting the roles of conserved genes and microbial community shifts in adapting to extreme environments. In situ exposure of shallow-water mussels to deep-sea conditions induced changes in their transcriptome and microbiome, with profiles gradually aligning with those of native deep-sea mussels, highlighting the conserved interplay between evolutionary adaptations and rapid adjustments. [ABSTRACT FROM AUTHOR]

The root-associated type II methanotrophs significantly contribute to CH4 oxidation-dependent N2 fixation. However, it is unclear whether type I methanotrophs are involved in CH4 oxidation and N2 fixation, especially in natural wetlands. So far, limited attention has given to root-associated active microorganisms. Here, metatranscriptomic analysis of root-associated microbes has been proposed to reveal the aerobic methanotrophs contributing to CH4 and nitrogen cycles in the roots of Phragmites australis grown in a natural wetland. Results showed Methylocystaceae (type II methanotrophs) and Methylococcaceae (type I methanotrophs) as major taxa (relative abundance, 14%) at transcription level. However, based on 16S rRNA gene sequencing, contribution of these taxa was < 1% at DNA level. Genes encoding methane monooxygenase (enzyme responsible for the first step of CH4 oxidation) were detected in Methylomonas (pmoCBA) and Methylosinus (mmoXYZCB). Furthermore, genes related to methanol dehydrogenase, formaldehyde dehydrogenase, and formate dehydrogenase were also detected in Methyosinus and Methylomonas, while mcrA gene was observed in Methanospirillum and Methanofollis. Moreover, nitrogenase structural genes, such as nifHDK, were found in Methylosinus (Methylocystaceae) and Methylomonas (Methylococcaceae). Minor nitrogenase genes were detected in Cyanothece, Lyngbya, Pelobacter and Smithella of Cyanobacteriaceae family. In addition, N2 fixing activity of P. australis was determined by analyzing the natural abundance of δ15N from June to August. The N2 fixing activity of P. australis increased in presence of CH4 in root system under 15N-N2 feeding. Metatranscriptomic analysis revealed that not only type II methanotrophs, but also type I methanotrophs oxidize CH4 and fix N2. [ABSTRACT FROM AUTHOR]

• Biofilter maintains optimal conditions for methane bacteria and oxidation. • Capillary barrier affects the design and function of the biofilter. • Proper acclimatization of MOL is paramount to ensure maximum efficiency. The City of Montreal has committed to achieve carbon neutrality by 2050. To meet this commitment, the city has adopted the Climate Plan 2020–2030, which includes the treatment of landfill gas (LFG). Within this framework, this research aimed to investigate the efficiency of a biofilter designed to treat high volumes of low-concentration LFG collected from lateral trenches at the Complexe Environnemental de Saint-Michel (CESM) in Montreal. The methane oxidation layer (MOL) of this biofilter, employed a material composed of 50% compost and 50% wood chips. Over a 54-week monitoring period, the system effectively maintained temperature conditions favorable to bacterial activity and methane oxidation. To assess the accuracy of predicting the hydraulic behavior of a methane oxidation biosystem (MOB) using numerical modeling, the biofilter was designed and constructed with specific features. In particular, the pore voids at the interface between the MOL and the gas distribution layer (GDL) were intentionally blocked along the downstream quarter of the biofilter length. This design ensures that water reaches the occlusion point due to the capillary barrier effect. Moisture content values remained within the expected range for most of the monitoring phase but increased with time. Despite this issue, the biofilter achieved an average efficiency higher than 95%. The findings underscore the capability of biosystems to manage substantial volumes of lean LFG, but also highlight the importance of acclimatizing the compost before exposure to maximum landfill load. [ABSTRACT FROM AUTHOR]

Despite covering <5% of Earth's terrestrial area, peatlands are crucial for global carbon storage and are hot spots of methane cycling. This study examined the dynamics of aerobic and anaerobic methane oxidation in two undisturbed peatlands: a fen and a spruce swamp forest. Using microcosm incubations, we investigated the effect of ammonium addition, at a level similar to current N pollution processes, on aerobic methane oxidation. Our findings revealed higher methane consumption rates in fen compared to swamp peat, but no effect of ammonium amendment on methane consumption was found. Members of Methylocystis and Methylocella were the predominant methanotrophs in both peatlands. Furthermore, we explored the role of ferric iron and sulfate as electron acceptors for the anaerobic oxidation of methane (AOM). AOM occurred without the addition of an external electron acceptor in the fen, but not in the swamp peat. AOM was stimulated by sulfate and ferric iron addition in the swamp peat and inhibited by ferric iron in the fen. Our findings suggest that aerobic methane oxidizers are not N-limited in these peatlands and that there is an intrinsic potential for AOM in these environments, partially facilitated by ferric iron and sulfate acting as electron acceptors. [ABSTRACT FROM AUTHOR]

Paddy fields are the main agricultural source of greenhouse gas methane (CH4) emissions. To enhance rice yield, various fertilization practices have been employed in rice paddies. However, the key microbial and abiotic factors driving CH4 emissions under different fertilization practices in paddy fields remain largely uncharted. This study conducted field experiments in a traditional double-cropping rice area in South China, utilizing five different fertilization practices to investigate the key factors influencing CH4 emissions. High-throughput sequencing and PICRUSt2 functional prediction were employed to investigate the contributions of soil physicochemical properties, CH4-metabolizing microorganisms (methanogens and methanotrophs), and key genes (mcrA and pmoA) on CH4 emissions. The results showed that CH4 emission fluxes exhibited seasonal variations, with consistent patterns of change observed across all treatments for both early- and late-season rice. Compared to the no-fertilization (NF) treatment, cumulative CH4 emissions were lower in early-season rice with green manure (GM) and straw returning (SR) treatments, as well as in late-season rice with GM treatment, while rice yields were maintained at higher levels. High-throughput sequencing analysis revealed that potential methanogens were primarily distributed among four orders: Methanobacteriales, Methanocellales, Methanomicrobiales, and Methanosarcinales. Furthermore, there was a significant positive correlation between the relative abundance of the CH4-related key gene mcrA and these microorganisms. Functional analysis indicated that these potential methanogens primarily produce methane through the acetoclastic and hydrogenotrophic pathways. Aerobic CH4-oxidizing bacteria, predominantly from the genus Methylocystis, were detected in all the treatments, while the CH4 anaerobic-oxidizing archaea ANME-1b was only detected in chemical fertilization (CF) and cow manure (CM) treatments. Our random forest analysis revealed that the relative abundance of two methanogens (Methanocellales and Methanosarcinales) and two environmental factors (pH and DOC) had significant impacts on the cumulative CH4 emissions. The variance decomposition analysis highlighted the CH4-metabolizing microorganisms explained 50% of the variance in the cumulative CH4 emissions, suggesting that they are the key microbial factors driving CH4 emissions. These findings provide guidance for the development of rational measures to reduce CH4 emissions in paddy fields. [ABSTRACT FROM AUTHOR]

Anaerobic ammonia oxidation (anammox) process is regarded as an efficient and cost-effective technology for nitrogen removal. Anammox bacteria typically coexist with other microorganisms, which highlights the necessity to optimize the system, improve the pollutant removal efficiency and maintain the system stability. This review mainly focused on the interaction effects of anammox bacteria with other functional bacteria, such as aerobic ammonia-oxidizing bacteria, sulphur-oxidizing bacteria, sulphate-reducing ammonia oxidation bacteria, denitrifying bacteria, denitrifying anaerobic methane oxidation microorganisms, denitrifying phosphate-accumulating organisms. This review provided support for the emerging insights that the synergistic effects of various functional bacteria related to nitrogen, phosphorus, sulphur, and carbon within the anammox system could be a promising direction for the development of wastewater treatment technologies. By considering the interplay and cooperation of these microorganisms, wastewater treatment systems could potentially achieve more comprehensive and efficient removal of multiple pollutants. Continued in-depth research and understanding of these interactions would be instrumental in exploring innovative and integrated solutions, ultimately aiming for a more effective and holistic approach to wastewater treatment. [ABSTRACT FROM AUTHOR]

The cultivation of microorganisms is important as it provides us an opportunity to explore the characteristics that can be used for a variety of applications. Methanotrophs oxidize methane and are one of the most challenging organisms to culture. In 2018, we cultured one of the largest methanotrophs within the gammaproteobacterial group (Type Ia), a novel genus and species, Methylocucumis oryzae, with large peculiar, elongated oval (cucumber-shaped) cells (~ 3–6 µm length × 1.5 µm breadth). We have described three strains of Methylocucumis oryzae (abbreviated as Mcu or Mcu oryzae) isolated from two flooded rice fields and recently from a stone quarry in Pune, all three locations are in Maharashtra state, Western India. Mcu is a mesophile and prefers lower temperatures for growth in the range 20–28 °C and does not grow above 37 °C. No other species of Methylocucumis have been reported from any other country and Mcu oryzae appears to be phylogenetically unique after 6 years of its initial report. Though the culture has certain challenges to grow on a larger scale due to its slow growth rate, it might have significant potential in methane mitigation, plant growth promotion, carotenoid production, etc. awaiting more detailed studies on this rare organism. Further optimization experiments to grow Mcu in large quantities might help us in developing environmental and biotechnological applications. [ABSTRACT FROM AUTHOR]

The genus Methylomarinum accommodates aerobic motile non-pigmented methanotrophic bacteria, which were isolated from marine habitats and require NaCl for growth. Until recently, this genus contained a single species, M. vadi. Here, we describe a novel Methylomarinum representative, strain Ch1-1T, obtained from the sediments of the River Chernavka at its confluence with the hypersaline Lake Elton, Russia. Strain Ch1-1T was represented by gram-negative, pink-pigmented, motile rods or ovoids, which multiplied by binary fission and possessed the particulate methane monooxygenase (pMMO). These bacteria grew on methane within the temperature range of 5–42°C (optimum at 30–35°C) and at рH 6.3–7.5 (optimum at 6.5–6.8). Growth on methanol was inconsistent. NaCl was required for growth, which was observed in liquid media only within a NaCl concentration range of 0.5–10% (w/v). Best growth was recorded at a NaCl concentration of 3.5–4.0% (w/v). The 16S rRNA gene sequence of strain Ch1-1T displayed 97.09–97.24% similarity to the corresponding gene fragments of described representatives of M. vadi. The genome of strain Ch1-1T was 4.8 Mb in size and contained 3 rRNA operons and about 4400 protein-coding genes, including the gene cluster pmoCAB coding for pMMO, a complete set of genes for the function of the ribulose monophosphate pathway as well as genes necessary for ectoine and sucrose biosynthesis. The DNA G+C content was 50.7 mol %. The average nucleotide identity determined for genomes of strain Ch1-1T and M. vadi IT-4T was 78.8%. Based on the number of genotypic and phenotypic differences, we propose to classify this isolate as representing a novel species of the genus Methylomarinum, M. roseum sp. nov. strain Ch1-1T (=VKM B-3852T = UQM 41855T) is the type strain of the newly proposed species. [ABSTRACT FROM AUTHOR]

Oxidation of methane by soil microorganisms is an important mechanism controlling the content of this potent greenhouse gas in the atmosphere. Agricultural soils operate under stressful conditions, and ammonium (N-fertilization) and drying (global warming) may have a significant impact on methane oxidation. In order to investigate how soil methanotrophs respond to drying–rewetting (DW), ammonium addition (100 mg/g) (A), and their combined action (MS), agricultural soil microcosms were incubated over the three months and methane oxidation was measured before and after perturbations, while community composition was monitoring using 16S rRNA gene sequencing. A significant decline in the methane-oxidation activity after perturbations was found, with subsequent restoration, and the combined treatment was more effective than the sum of individual treatments, indicating a synergistic effect. After rewetting, the structure of the bacterial community returned to pre-dry-down levels, but the application of ammonia and combined action lead to irreversible changes in the structure of soil methanotrophic communities. Methanotroph Methylomicrobium were significantly reduced under disturbances, while there was a significant increase in the representation of Methylobacter accompanied by the facultative methylotroph Methylovorus. We concluded that methanotrophic communities in agricultural soil demonstrated flexibility, and even when the abundance of dominant populations drops, ecosystem functions can recover. [ABSTRACT FROM AUTHOR]

The seepage of gaseous compounds from underground reservoirs towards the surface causes abnormalities in the population of microbial communities that consume light hydrocarbons on the surface of the reservoir. This microbial population can serve as indicators for determining the location of gas reservoirs prior to drilling operations. In this study, the simulation of methane gas leakage in the sediments of the Persian Gulf was conducted using a laboratory model. The objective of this simulation was to identify the microbial population consuming methane within the sediments of the Persian Gulf, aiding in the exploration of gas reserves. Continuous injection of methane gas into the system was performed for a period of 3 months to enrich the microbial consortia consuming methane. Subsequently, the microbial population was identified using next-generation sequencing (NGS) analysis. The results indicated that, based on the 16S rRNA sequencing dataset, aerobic methanotrophs, including genera Methylobacter , Methylomarinum , Methylomicrobium, Methylomonas , and Methylophage , were the dominant microbial group on the surface of the sediments. Additionally, anaerobic methane oxidation archaea in sediments were performed by ANME-2 and ANME-3 clades. The findings demonstrate that these microbial communities are capable of coexistence and thrive in long-term exposure to methane in the sediments of the Persian Gulf. Identifying this microbial pattern, alongside other geophysical and geological data, can increase the success rate of gas reservoir exploration. [ABSTRACT FROM AUTHOR]

Introduction: Organic wastes are composted to increase their plant nutritional value, but little is known about how this might alter the bacterial and archaeal community structure and their genes. Methods: Cow manure was collected from three local small-scale farmers and composted under controlled conditions, while the bacterial and archaeal communities were determined using shotgun metagenomics at the onset and after 74 days of composting. Results: The bacterial, archaeal, methanogen, methanotrophs, methylotroph, and nitrifying community structures and their genes were affected by composting for 74 days, but the original composition of these communities determined the changes. Most of these archaeal and bacterial groups showed considerable variation after composting and between the cow manures. However, the differences in the relative abundance of their genes were much smaller compared to those of the archaeal or bacterial groups. Discussion: It was found that composting of different cow manures did not result in similar bacterial or archaeal communities, and the changes that were found after 74 days were defined by the original populations. However, more research is necessary to determine if other composting conditions will give the same results. [ABSTRACT FROM AUTHOR]

Wetland systems are known methane (CH4) sources. However, flooded rice fields are periodically drained. The paddy soils can absorb atmospheric CH4 during the dry seasons due to high-affinity methane-oxidizing bacteria (methanotroph). Atmospheric CH4 uptake can be induced during the low-affinity oxidation of high-concentration CH4 in paddy soils. Multiple interacting factors control atmospheric CH4 uptake in soil ecosystems. Broader biogeographical data are required to refine our understanding of the biotic and abiotic factors related to atmospheric CH4 uptake in paddy soils. Thus, here, we aimed to assess the high-affinity CH4 oxidation activity and explored the community composition of active atmospheric methanotrophs in nine geographically distinct Chinese paddy soils. Our findings demonstrated that high-affinity oxidation of 1.86 parts per million by volume (ppmv) CH4 was quickly induced after 10,000 ppmv high-concentration CH4 consumption by conventional methanotrophs. The ratios of 16S rRNA to rRNA genes (rDNA) for type II methanotrophs were higher than those for type I methanotrophs in all acid-neutral soils (excluding the alkaline soil) with high-affinity CH4 oxidation activity. Both the 16S rRNA:rDNA ratios of type II methanotrophs and the abundance of 13C-labeled type II methanotrophs positively correlated with high-affinity CH4 oxidation activity. Soil abiotic factors can regulate methanotrophic community composition and atmospheric CH4 uptake in paddy soils. High-affinity methane oxidation activity, as well as the abundance of type II methanotroph, negatively correlated with soil pH, while they positively correlated with soil nutrient availability (soil organic carbon, total nitrogen, and ammonium-nitrogen). Our results indicate the importance of type II methanotrophs and abiotic factors in atmospheric CH4 uptake in paddy soils. Our findings offer a broader biogeographical perspective on atmospheric CH4 uptake in paddy soils. This provides evidence that periodically drained paddy fields can serve as the dry-season CH4 sink. This study is anticipated to help in determining and devising greenhouse gas mitigation strategies through effective farm management in paddy fields. [ABSTRACT FROM AUTHOR]

Trivalent iron (Fe3+) could participate in methane (CH4) oxidation as an electron acceptor under anaerobic conditions, but the kinetic process remains unknown in landfills, and the understanding of metabolic pathway of Fe3+-dependent anaerobic methane oxidation (Fe-DAMO) is still limited. In this study, the dual-substrate (CH4-Fe3+) kinetic model of CH4 oxidation is obtained with Vmax (7.35 ± 0.4184)μmol/(kg d), half-saturation constant K m , CH 4 (16.6699 ± 2.3940)ppmv, and K m , Fe 3 + (0.00107 ± 0.0002g/g). Microbial community analysis shows that Methanobacteriales and Clostridia are dominant microorganisms of Fe-DAMO. PICRUSt analysis confirms that the metabolic pathway of AMO is the reverse CH4 production pathway. The results provide a new perspective for CH4 biodegradation in landfills and offer a better understanding of Fe-DAMO process. [ABSTRACT FROM AUTHOR]

Biotechnology continues to drive innovation in the production of pharmaceuticals, biofuels, and other valuable compounds, leveraging the power of microbial systems for enhanced yield and sustainability. Genome-scale metabolic (GSM) modeling has become an essential approach in this field, which enables a guide for targeting genetic modifications and the optimization of metabolic pathways for various industrial applications. While single-species GSM models have traditionally been employed to optimize strains like Escherichia coli and Lactococcus lactis, the integration of these models into community-based approaches is gaining momentum. Herein, we present a pipeline for community metabolic modeling with a user-friendly GUI, applying it to analyze interactions between Methylococcus capsulatus, a biotechnologically important methanotroph, and Escherichia coli W3110 under oxygen- and nitrogen-limited conditions. We constructed models with unmodified and homoserine-producing E. coli strains using the pipeline implemented in the original BioUML platform. The E. coli strain primarily utilized acetate from M. capsulatus under oxygen limitation. However, homoserine produced by E. coli significantly reduced acetate secretion and the community growth rate. This homoserine was taken up by M. capsulatus, converted to threonine, and further exchanged as amino acids. In nitrogen-limited modeling conditions, nitrate and ammonium exchanges supported the nitrogen needs, while carbon metabolism shifted to fumarate and malate, enhancing E. coli TCA cycle activity in both cases, with and without modifications. The presence of homoserine altered cross-feeding dynamics, boosting amino acid exchanges and increasing pyruvate availability for M. capsulatus. These findings suggest that homoserine production by E. coli optimizes resource use and has potential for enhancing microbial consortia productivity. [ABSTRACT FROM AUTHOR]

Mitigating methane (CH4) emissions using methanotrophs (methane-oxidizing bacteria, MOB), is a simple, energy efficient and cheap technology. The abundance and distribution of MOB in the environmental samples is critical for efficient removal of emitted CH4 from any source. This study evaluated the performance of farm soils without and with cheap, easily accessible bulking materials as sustainable hybrid biofilter media. Soil-only biofilters removed up to 865 ± 19 g CH4 m−3 d−1 with well-drained organic carbon-rich soils compared with 264 ± 14 g CH4 m−3 d−1 for poorly drained soil. The removal efficiency decreased with increasing flow rate (0.16→0.24 L min−1) and subsequent priming could not return soil biofilters to their previous removal rate. Hybrid biofilters using organic, carbon-rich soils and compost removed up to 2698 g CH4 m−3 d−1 (flow rate 0.35 L min−1). Increasing CH4 flow rates also reduced their efficiency, but the hybrid biofilters with compost quickly regained most of their efficiency and removed up to 2262 g CH4 m−3 d−1 (flow rate 0.3 L min−1) after remixing of biofilter media. These results show that hybrid biofilters removed higher CH4 than soil-only biofilters and were also more resilient. The MOB gene abundance results complement the CH4 removal capacity of both soil-only and hybrid biofilter materials used. The more aerobic, carbon-rich soils had more abundant MOB than the poorly drained soil. The most porous hybrid biofilter with compost and more available nutrients to sustain bacterial growth and activity had the highest MOB abundance and removed the most CH4. [ABSTRACT FROM AUTHOR]

Rice paddies account for approximately 9% of human‐induced methane (CH4) emissions. Nitrogen (N) fertilization affects CH4 emissions from paddy soils through several mechanisms, leading to conflicting results in field experiments. The primary drivers of these N‐related effects remain unclear and the contribution of N fertilization to CH4 emissions from the rice paddies has not yet been quantified for global area. This uncertainty contributes to significant challenges in projecting global CH4 emissions and hinders the development of effective local mitigation strategies. Here, we show through a meta‐analysis and experiments that the impact of N fertilization on CH4 emissions from rice paddies can be largely predicted by soil pH. Specifically, N fertilization stimulates CH4 emissions most strongly in acidic soils by accelerating organic matter decomposition and increasing the activities of methanogens. Accounting for the interactions between soil pH and N fertilization, we estimate that N fertilization has raised current area‐scaled and yield‐scaled CH4 emissions across the total global paddy area by 52% and 8.2%, respectively. Our results emphasize the importance of alleviating soil acidification and sound N management practices to mitigate global warming. [ABSTRACT FROM AUTHOR]

The production of methane in coastal sediments and its release to the water column is intensified by anthropogenic eutrophication and bottom water hypoxia, and it is still uncertain whether methane emissions to the atmosphere will be enhanced. Here, we assess seasonal variations in methane dynamics in a eutrophic, seasonally euxinic coastal basin (Scharendijke, Lake Grevelingen). In-situ benthic chamber incubations reveal high rates of methane release from the sediment to the water column (74–163 mmol m−2 d−1) during monthly measurements between March and October 2021. Comparison of these in-situ total benthic methane fluxes and calculated diffusive fluxes point towards a major role for ebullition. In spring and fall, when the water column was oxic, microbial removal of dissolved methane occurred aerobically in the bottom water. In summer, in contrast, dissolved methane accumulated to concentrations of up to 67 μmol L−1 below the oxycline. Shifts in δ 13C–CH 4 and δ D-CH 4 towards higher values and the abundant presence of methane oxidizing bacteria point towards removal of methane around the oxycline, likely through both aerobic and anaerobic pathways, with the latter possibly linked to iron oxide reduction. Shifts in δ 13C–CH 4 and δ D-CH 4 to lower values above the oxycline indicate that bubble dissolution contributed to dissolved methane. Methane emissions to the atmosphere were observed in all seasons with the highest, in-situ measured diffusive fluxes (1.2 mmol m−2 d−1) upon the onset of water column mixing at the end of summer. Methane release events during the measurement of in-situ water-air fluxes and model calculations point towards a flux of methane to the atmosphere in the form of bubbles, which bypass the microbial methane filter. The model calculations suggest a potential year-round ebullitive methane flux between 30 and 120 mmol m−2 d−1. We conclude that methane emissions from eutrophic coastal systems may be much higher than previously thought because of ebullition. [ABSTRACT FROM AUTHOR]

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Estuarine wetlands harbor considerable carbon stocks, but rising sea levels could affect their ability to sequester soil carbon as well as their potential to emit methane (CH4). While sulfate loading from seawater intrusion may reduce CH4 production due to the higher energy yield of microbial sulfate reduction, existing studies suggest other factors are likely at play. Our study of 11 wetland complexes spanning a natural salinity and productivity gradient across the San Francisco Bay and Delta found that while CH4 fluxes generally declined with salinity, they were highest in oligohaline wetlands (ca. 3-ppt salinity). Methanogens and methanogenesis genes were weakly correlated with CH4 fluxes but alone did not explain the highest rates observed. Taxonomic and functional gene data suggested that other microbial guilds that influence carbon and nitrogen cycling need to be accounted for to better predict CH4 fluxes at landscape scales. Higher methane production occurring near the freshwater boundary with slight salinization (and sulfate incursion) might result from increased sulfate-reducing fermenter and syntrophic populations, which can produce substrates used by methanogens. Moreover, higher salinities can solubilize ionically bound ammonium abundant in the lower salinity wetland soils examined here, which could inhibit methanotrophs and potentially contribute to greater CH4 fluxes observed in oligohaline sediments.IMPORTANCELow-level salinity intrusion could increase CH4 flux in tidal freshwater wetlands, while higher levels of salinization might instead decrease CH4 fluxes. High CH4 emissions in oligohaline sites are concerning because seawater intrusion will cause tidal freshwater wetlands to become oligohaline. Methanogenesis genes alone did not account for landscape patterns of CH4 fluxes, suggesting mechanisms altering methanogenesis, methanotrophy, nitrogen cycling, and ammonium release, and increasing decomposition and syntrophic bacterial populations could contribute to increases in net CH4 flux at oligohaline salinities. Improved understanding of these influences on net CH4 emissions could improve restoration efforts and accounting of carbon sequestration in estuarine wetlands. More pristine reference sites may have older and more abundant organic matter with higher carbon:nitrogen compared to wetlands impacted by agricultural activity and may present different interactions between salinity and CH4. This distinction might be critical for modeling efforts to scale up biogeochemical process interactions in estuarine wetlands.

Methanotrophic bacteria are promising hosts for methane bioconversion to biochemicals or bioproducts. However, due to limitations associated with long genetic manipulation timelines and, lack of choice in genetic tools required for strain engineering, methanotrophs are currently not employed for bioconversion technologies. In this study, a rapid and reproducible electroporation protocol is developed for type 1 methanotroph, Methylotuvimicrobium alcaliphilum using common laboratory solutions, analyzing optimal electroshock voltages and post-shock cell recovery time. Successful reproducibility of the developed method was achieved when different replicative plasmids were assessed on lab adapted vs. wild-type M. alcaliphilum strains (DASS vs. DSM19304). Overall, a ∼ 3-fold decrease in time is reported with use of electroporation protocol developed here, compared to conjugation, which is the traditionally employed approach. Additionally, an inducible (3-methyl benzoate) and a constitutive (sucrose phosphate synthase) promoter is characterized for their strength in driving gene expression.

Anthropogenic activities have escalated CH4 emissions, exacerbating global warming, yet specialized bacteria known as Methanotrophs play a key role in mitigating atmospheric CH4 levels by consuming 30-70% of emitted methane. This study focuses on exploring the culturable methanotrophic population within Muthukuda mangrove sediments, an unexplored reservoir of methanotrophic diversity. The sediment sample yielded a methanotrophic bacterial count of 1.5 x 103 CFU/g, leading to the selection of three unique bacterial morphotypes (NCT270, NCT271, and NCT272) for in-depth investigation. Optimal growth was observed at pH 8, with peak growth at 30°C, while extreme temperatures of 4°C and 40°C inhibited growth across all isolates. Salinity levels between 20 and 30 ppt supported optimal growth, with strains displaying tolerance to various stressors. Methane served as the sole carbon source for all experiments, with positive urease production noted after 7 days of incubation. Microscopic and biochemical analyses suggested the classification of strains NCT270, NCT271, and NCT272 within Group I methanotrophic genera: Methylomicrobium, Methyloscarcina, and Methylomonas, respectively. BLASTn analysis of 16S rRNA gene sequences shared high similarities with known methanotrophic species Methyloscarcina fibrate (ON834586) with 99.28%, Methylomicrobium album (ON834587) with 98.77% and Methylomonas methanica (ON834588) with 99.15%. The resulting insights enhance our understanding of culturable methanotrophic diversity and underscore its potential for environmental applications.

Terrestrial mud volcanoes represent surface features of channels for subsurface methane transport and, therefore, constitute an important source of methane emission from natural environments. How microbial processes regulate methane emissions in terrestrial mud volcanoes has yet to be fully addressed. This study demonstrated the geochemical characteristics and microbial communities of four mud volcano and seep sites in two geological settings of Sicily, Italy. At sites within the accretionary wedge that exhibited higher methane and sulfate concentrations, the communities were dominated by members capable of catalyzing methane and sulfate metabolisms and organic degradation. In particular, both anaerobic and aerobic methanotrophs were abundant and their abundance distribution coincided with the geochemical transition. In contrast, the sites near Mount Etna were characterized by high fluid salinity, CO2, and low methane and sulfate concentrations, with communities consisting of halophilic organic degraders and sulfur metabolizers, along with a minor presence of aerobic methanotrophs. Substantial variations in community composition and geochemistry across spatial and vertical redox gradients suggest that physicochemical contexts imposed by the geology, fluid path, and source characteristics play a vital role in shaping community composition and cycling of methane, sulfur and organic carbon in Sicily mud volcanoes. [ABSTRACT FROM AUTHOR]

Atmospheric methane oxidizing bacteria (atmMOB) constitute the sole biological sink for atmospheric methane. Still, the physiological basis allowing atmMOB to grow on air is not well understood. Here we assess the ability and strategies of seven methanotrophic species to grow with air as sole energy, carbon, and nitrogen source. Four species, including three outside the canonical atmMOB group USCα, enduringly oxidized atmospheric methane, carbon monoxide, and hydrogen during 12 months of growth on air. These four species exhibited distinct substrate preferences implying the existence of multiple metabolic strategies to grow on air. The estimated energy yields of the atmMOB were substantially lower than previously assumed necessary for cellular maintenance in atmMOB and other aerobic microorganisms. Moreover, the atmMOB also covered their nitrogen requirements from air. During growth on air, the atmMOB decreased investments in biosynthesis while increasing investments in trace gas oxidation. Furthermore, we confirm that a high apparent specific affinity for methane is a key characteristic of atmMOB. Our work shows that atmMOB grow on the trace concentrations of methane, carbon monoxide, and hydrogen present in air and outlines the metabolic strategies that enable atmMOB to mitigate greenhouse gases. Atmospheric methane-oxidizing bacteria constitute the sole biological sink for atmospheric methane. Here, Schmider et al. assess the ability and strategies of seven methanotrophic species to grow with air as sole energy, carbon, and nitrogen source, showing that these bacteria can grow on the trace concentrations of methane, carbon monoxide, and hydrogen present in air. [ABSTRACT FROM AUTHOR]

Methane production in ruminants is primarily due to the conversion of metabolic hydrogen (H2), produced during anaerobic microbial fermentation, into methane by ruminal methanogens. While this process plays a crucial role in efficiently disposes of H2, it also contributes to environmental pollution and eliminating methane production in the rumen has proven to be challenging. This study investigates the use of probiotics, specifically propionate-producing bacteria, to redirect accumulated H2 in a methane-mitigated environment. For this objective, we supplemented experimental groups with Lactiplantibacillus plantarum and Megasphaera elsdenii for the reinforced acrylate pathway (RA) and Selenomonas ruminantium and Acidipropionibacterium thoenii for the reinforced succinate pathway (RS), as well as a consortium of all four strains (CB), with the total microbial concentration at 1.0 × 1010 cells/mL. To create a methane-mitigated environment, 2-bromoethanesulfonate (BES) was added to all experimental groups at a dose of 15 mg/0.5 g of feed. BES reduced methane production by 85% in vitro, and the addition of propionate-producing bacteria with BES further decreased methane emission by up to 94% compared with the control (CON) group. Although BES did not affect the alpha diversity of the ruminal bacteriome, it reduced total volatile fatty acid production and altered beta diversity of ruminal bacteriota, indicating microbial metabolic adaptations to H2 accumulation. Despite using different bacterial strains targeting divergent metabolic pathways (RA and RS), a decrease in the dominance of the [Eubacterium] ruminantium group suggesting that both approaches may have a similar modulatory effect. An increase in the relative abundance of Succiniclasticum in the CB group suggests that propionate metabolism is enhanced by the addition of a propionate-producing bacterial consortium. These findings recommend using a consortium of propionate-producing bacteria to manage H2 accumulation by altering the rumen bacteriome, thus mitigating the negative effects of methane reduction strategies. [ABSTRACT FROM AUTHOR]

The microbial diversity associated with terrestrial groundwater seepage through permafrost soils is tightly coupled to the geochemistry of these fluids. Terrestrial alkaline methane seeps from Lagoon Pingo, Central Spitsbergen (78°N) in Norway, with methane-saturated and oxygen-limited groundwater discharge providing a potential habitat for methanotrophy. Here, we report on the microbial community's comparative analyses and distribution patterns at two sites close to Lagoon Pingo's methane emission source. To target methane-oxidizing bacteria from this system, we analysed the microbial community pattern of replicate samples from two sections near the main methane seepage source. DNA extraction, metabarcoding and subsequent sequencing of 16S rRNA genes revealed microbial communities where the major prokaryotic phyla were Pseudomonadota (42–47%), Gemmatimonadota (4–14%) and Actinobacteriota (7–11%). Among the Pseudomonadota, members of the genus Methylobacter were present at relative abundances between 1.6 and 4.7%. Enrichment targeting the methane oxidising bacteria was set up using methane seep sediments as inoculum and methane as the sole carbon and energy source, and this resulted in the isolation of a novel psychrophilic methane oxidizer, LS7-T4AT. The optimum growth temperature for the isolate was 13 °C and the pH optimum was 8.0. The morphology of cells was short rods, and TEM analysis revealed intracytoplasmic membranes arranged in stacks, a distinctive feature for Type I methanotrophs in the family Methylomonadaceae of the class Gammaproteobacteria. The strain belongs to the genus Methylobacter based on high 16S rRNA gene similarity to the psychrophilic species of Methylobacter psychrophilus Z-0021T (98.95%), the psychrophilic strain Methylobacter sp. strain S3L5C (99.00%), and the Arctic mesophilic species of Methylobacter tundripaludum SV96T (99.06%). The genome size of LS7-T4AT was 4,338,157 bp with a G + C content of 47.93%. The average nucleotide identities (ANIb) of strain LS7-T4AT to 10 isolated strains of genus Methylobacter were between 75.54 and 85.51%, lower than the species threshold of 95%. The strain LS7-T4AT represents a novel Arctic species, distinct from other members of the genus Methylobacter, for which the name Methylobacter svalbardensis sp. nov. is proposed. The type of strain is LS7-T4AT (DSMZ:114308, JCM:39463). [ABSTRACT FROM AUTHOR]

The effects of fallow season water and straw management on methane (CH4) emissions during the fallow season and the subsequent rice-growing season are rarely reported, and the underlying microbial mechanisms remain unclear. A field experiment was conducted with four treatments: (1) fields flooded in both the fallow and rice seasons (FF), (2) fields drained in the fallow season and flooded in the rice season (DF), (3) FF with straw retention (FFS), and (4) DF with straw retention (DFS). The CH4 emissions in fields under different water and straw treatments were monitored using the static closed chamber method. Methanogenic and methanotrophic communities in these fields were examined using terminal restriction fragment length polymorphism (T-RFLP) analysis based on the mcrA gene and pmoA gene encoding methyl coenzyme M reductase and particulate methane monooxygenase, respectively. The results showed that CH4 emissions were significantly affected by water management, straw retention, season, and their interactions. Over 80% of CH4 emissions occurred during the rice season. Field drainage during the fallow season reduced CH4 emissions by 47.0% and 53.8% with and without straw during the rice season, respectively. Water management altered the abundance and composition of methanogens and methanotrophs, whereas the effects of straw retention were less pronounced. The quantitative polymerase chain reaction (qPCR) assay revealed that field drainage in the fallow season decreased the mcrA gene abundance by 30.0% and 23.2% with and without straw in rice season, respectively, and increased the pmoA gene abundance by 108.9% and 213.7% with and without straw in rice season, respectively. CH4 flux was significantly positively associated with mcrA gene copy number and the ratio of mcrA to pmoA gene copy number, whereas it was significantly negatively correlated with the pmoA gene copy number. Results indicated that fallow drainage greatly decreased CH4 emission not only during the fallow season but also during the subsequent rice season by altering the community composition of methanogens and methanotrophs. These findings provide scientific insight into the role of water and straw management in controlling CH4 emissions through microbial community dynamics. [ABSTRACT FROM AUTHOR]

The potential positive feedback between global aquatic deoxygenation and methane (CH4) emission emphasizes the importance of understanding CH4 cycling under O2‐limited conditions. Increasing observations for aerobic CH4‐oxidizing bacteria (MOB) under anoxia have updated the prevailing paradigm that MOB are O2‐dependent; thus, clarification on the metabolic mechanisms of MOB under anoxia is critical and timely. Here, we mapped the global distribution of MOB under anoxic aquatic zones and summarized four underlying metabolic strategies for MOB under anoxia: (a) forming a consortium with oxygenic microorganisms; (b) self‐generation/storage of O2 by MOB; (c) forming a consortium with non‐oxygenic heterotrophic bacteria that use other electron acceptors; and (d) utilizing alternative electron acceptors other than O2. Finally, we proposed directions for future research. This study calls for improved understanding of MOB under anoxia, and underscores the importance of this overlooked CH4 sink amidst global aquatic deoxygenation. [ABSTRACT FROM AUTHOR]

Methanotrophs are bacteria that consume methane (CH4) as their sole carbon and energy source. These microorganisms play a crucial role in the carbon cycle by metabolizing CH4 (the greenhouse gas), into cellular biomass and carbon dioxide (CO2). Polyhydroxyalkanoates (PHAs) are biopolymers produced by various microorganisms, including methanotrophs. PHA production using methanotrophs is a promising strategy to address growing concerns regarding plastic pollution and the need for sustainable, biodegradable materials. Various factors, including nutrient availability, environmental conditions, and metabolic engineering strategies, influence methanotrophic production. Nutrient limitations, particularly those of nitrogen or phosphorus, enhance PHA production by methanotrophs. Metabolic engineering approaches, such as the overexpression of key enzymes involved in PHA biosynthesis or the disruption of competing pathways, can also enhance PHA yields by methanotrophs. Overall, PHA production by methanotrophs represents a sustainable and versatile approach for developing biomedical materials with numerous potential applications. Additionally, alternative feedstocks, such as industrial waste streams or byproducts can be explored to improve the economic feasibility of PHA production. This review briefly describes the potential of methanotrophs to produce PHAs, with recent updates and perspectives. [ABSTRACT FROM AUTHOR]

AbstractThis study explores a novel enzymatic pretreatment approach in anaerobic reactors for dairy wastewater, using lipase AY Amano to enhance methane production and modify microbial and archaeal community composition. Batch and semi-batch reactors with a total volume of 2000 mL were used to treat dairy wastewater with initial COD of 2000 and 15,000 mg L−1, respectively. In a new novel approach, the semi-batch reactors underwent a three-phase operation: 30 days of acclimation, 30 days of rest, and 30 days of active operation. Adding lipase (0.05% wv−1) as a pretreatment significantly increased methane yield over the 90 days by 135–138% compared with the control (without enzyme addition). The organic loading rate reached 0.22 g COD day−1 L−1. Furthermore, 30 days after the end of the semi-batch reactor approach (120 days from the start), reusing sludge in batch reactors increased methane yield by 114–122% compared to the control. This increase was linked to the emergence and shift of new methanogenic communities within the sludge. Integrating hydrolytic enzymes into the anaerobic treatment enhances performance and sustainability by fostering methanogen-enriched microbial communities. This is crucial for maximizing methane production but may increase costs, requiring further economic feasibility research. [ABSTRACT FROM AUTHOR]

Background: Silage emits climate- and environment-relevant gases during fermentation and feed-out periods. This trial aimed to determine the unknown carbon dioxide (CO2), methane, nitrous oxide, ethanol, and ethyl acetate emissions of constant maize silage material over both periods. The results will be published in two consecutive articles (Part A: anaerobic fermentation period, Part B: aerobic storage period). Methods: The untreated control (CON) was compared with the chemical additive treatment (CHE; 0.5 g sodium benzoate and 0.3 g potassium sorbate per kg fresh matter) and the biological additive treatment (BIO; 108 colony-forming units (CFU) Lentilactobacillus buchneri and 107 CFU Lactiplantibacillus plantarum per kg fresh matter). Barrel silos (n = 4) were connected to gas bags to quantify gas formation during anaerobic fermentation (30 or 135 ensiling days). Glass jar silos (n = 12) were used for laboratory silage analysis. Results: CHE produced significantly (p < 0.05) less gas (6.7 ± 0.3 L per kg dry matter ensiled material (kgDM) until ensiling day 14.0 ± 0.0) and ethanol (8.6 ± 1.5 mg kgDM–1) than CON did (8.5 ± 0.2 L kgDM–1 until ensiling day 19.5 ± 6.4; 12.2 ± 1.5 (mg ethanol) kgDM–1). BIO indicates prolonged gas formation (9.1 ± 0.9 L kgDM–1 until ensiling day 61.3 ± 51.9; 12.0 ± 2.1 mg kgDM–1). CO2 is the main component of the gas formed. All treatments formed methane and nitrous oxide in small quantities. CON emitted significantly more CO2eq emissions than BIO and less than CHE (p < 0.05). Additives had no effect on ethyl acetate gas emissions. For BIO, ethanol concentrations in the material (rS = 0.609, p < 0.05) and gas quantities (rS = 0.691, p < 0.05) correlate with ethyl acetate gas quantities. All the treatments exhibited decreasing gas and CO2 quantities, and the dry matter mass increased between ensiling days 14 and 30 (− 0.810 ≤ rS ≤ 0.442; p < 0.05 to p = 0.20). Conclusion: Silage generates climate- and environmental-relevant gases during fermentation and silage additives affect this pattern. Gas formation exceeds the fixation potential, and the carbon footprint of silage fermentation is negative. [ABSTRACT FROM AUTHOR]

Methanotrophs are the sole biological sink of methane. Volatile organic compounds (VOCs) produced by heterotrophic bacteria have been demonstrated to be a potential modulating factor of methane consumption. Here, we identify and disentangle the impact of the volatolome of heterotrophic bacteria on the methanotroph activity and proteome, using Methylomonas as model organism. Our study unambiguously shows how methanotrophy can be influenced by other organisms without direct physical contact. This influence is mediated by VOCs (e.g. dimethyl-polysulphides) or/and CO2 emitted during respiration, which can inhibit growth and methane uptake of the methanotroph, while other VOCs had a stimulating effect on methanotroph activity. Depending on whether the methanotroph was exposed to the volatolome of the heterotroph or to CO2, proteomics revealed differential protein expression patterns with the soluble methane monooxygenase being the most affected enzyme. The interaction between methanotrophs and heterotrophs can have strong positive or negative effects on methane consumption, depending on the species interacting with the methanotroph. We identified potential VOCs involved in the inhibition while positive effects may be triggered by CO2 released by heterotrophic respiration. Our experimental proof of methanotroph–heterotroph interactions clearly calls for detailed research into strategies on how to mitigate methane emissions. [ABSTRACT FROM AUTHOR]

Fish meal (FM) replacement is essential for the sustainable expansion of aquaculture. This study focussed on the feasibility of replacing FM with a single‐cell protein (SCP) derived from methanotrophic bacteria (Methylococcus capsulatus, Bath) in barramundi fry (Lates calcarifer). Three isonitrogenous and isoenergetic diets were formulated with 0%, 6.4% and 12.9% inclusion of the SCP, replacing FM by 0%, 25% and 50%. Barramundi fry (initial body weight 2.5 ± 0.1 g) were fed experimental diets for 21 days to assess growth performance, gut microbiome composition and gut histopathology. Our findings revealed that both levels of SCP inclusion induced detrimental effects in barramundi fry, including impaired growth and reduced survival compared with the control group (66.7% and 71.7% survival in diets replacing FM with SCP by 25% and 50%, respectively; p <.05). Both dietary treatments presented mild necrotizing enteritis with subepithelial oedema and accumulation of PAS positive, diastase resistant droplets within hepatocytes (ceroid hepatopathy) and pancreatic atrophy. Microbiome analysis revealed a marked shift in the gut microbial community with the expansion of potential opportunistic bacteria in the genus Aeromonas. Reduced overall performance in the highest inclusion level (50% SCP) was primarily associated with reduced feed intake, likely related to palatability issues, albeit pathological changes observed in gut and liver may also play a role. Our study highlights the importance of meticulous optimization of SCP inclusion levels in aquafeed formulations, and the need for species and life‐stage specific assessments to ensure the health and welfare of fish in sustainable aquaculture practices. [ABSTRACT FROM AUTHOR]

Methane is the second largest contributor to global warming after carbon dioxide. Once it is released into the atmosphere, methane lingers for over 10 years, during which it traps heat, contributes to the formation of ground-level ozone, and affects air quality adversely. Conversely, methane has some benefits that could be harnessed to address its impact on the environment while utilizing it for good. Methane's significant role in global warming and potential for energy production and other beneficial applications necessitate the adoption of innovative solutions to remediate the gas from the atmosphere and harness some of its benefits. This article explores Methylococcus capsulatus, a methanotrophic bacterium, and its potential for revolutionizing sustainable methane capture and utilization. With its unique metabolic abilities, M. capsulatus efficiently oxidizes methane, making it a promising candidate for biotechnological applications. We review current research in its current and potential applications in methane capture and utilization, emphasizing key characteristics, implementation challenges, benefits, and limitations in methane capture and conversion. We also highlight the importance of interdisciplinary collaborations and technological advancements in synthetic biology to maximize its energy production potential. Our article analyzes M. capsulatus' role in addressing methane-related environmental concerns and advancing sustainable energy solutions. [ABSTRACT FROM AUTHOR]

Anthropogenic activities have escalated CH4 emissions, exacerbating global warming, yet specialized bacteria known as Methanotrophs play a key role in mitigating atmospheric CH4 levels by consuming 30-70% of emitted methane. This study focuses on exploring the culturable methanotrophic population within Muthukuda mangrove sediments, an unexplored reservoir of methanotrophic diversity. The sediment sample yielded a methanotrophic bacterial count of 1.5 x 103 CFU/g, leading to the selection of three unique bacterial morphotypes (NCT270, NCT271, and NCT272) for in-depth investigation. Optimal growth was observed at pH 8, with peak growth at 30°C, while extreme temperatures of 4°C and 40°C inhibited growth across all isolates. Salinity levels between 20 and 30 ppt supported optimal growth, with strains displaying tolerance to various stressors. Methane served as the sole carbon source for all experiments, with positive urease production noted after 7 days of incubation. Microscopic and biochemical analyses suggested the classification of strains NCT270, NCT271, and NCT272 within Group I methanotrophic genera: Methylomicrobium, Methyloscarcina, and Methylomonas, respectively. BLASTn analysis of 16S rRNA gene sequences shared high similarities with known methanotrophic species Methyloscarcina fibrate (ON834586) with 99.28%, Methylomicrobium album (ON834587) with 98.77% and Methylomonas methanica (ON834588) with 99.15%. The resulting insights enhance our understanding of culturable methanotrophic diversity and underscore its potential for environmental applications. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) produces useful biogas and waste streams with high levels of dissolved methane (CH4) and ammonium (NH4+), among other nutrients. Membrane biofilm reactors (MBfRs), which support dissolved methane oxidation in the same reactor as simultaneous nitrification and denitrification (ME-SND), are a potential bubble-less treatment method. Here, we demonstrate ME-SND taking place in single-stage, AD digestate liquid-fed MBfRs, where oxygen (O2) and supplemental CH4 were delivered via pressurized membranes. The effects of two O2 pressures, leading to different O2 fluxes, on CH4 and N removal were examined. MBfRs achieved up to 98% and 67% CH4 and N removal efficiencies, respectively. The maximum N removal rates ranged from 57 to 94 mg N L−1 d−1, with higher overall rates observed in reactors with lower O2 pressures. The higher-O2-flux condition showed NO2− as a partial nitrification endpoint, with a lower total N removal rate due to low N2 gas production compared to lower-O2-pressure reactors, which favored complete nitrification and denitrification. Membrane biofilm 16S rRNA amplicon sequencing showed an abundance of aerobic methanotrophs (especially Methylobacter, Methylomonas, and Methylotenera) and enrichment of nitrifiers (especially Nitrosomonas and Nitrospira) and anammox bacteria (especially Ca. Annamoxoglobus and Ca. Brocadia) in high-O2 and low-O2 reactors, respectively. Supplementation of the influent with nitrite supported evidence that anammox bacteria in the low-O2 condition were nitrite-limited. This work highlights coupling of aerobic methanotrophy and nitrogen removal in AD digestate-fed reactors, demonstrating the potential application of ME-SND in MBfRs for the treatment of AD's residual liquids and wastewater. Sensor-based tuning of membrane O2 pressure holds promise for the optimization of bubble-less treatment of excess CH4 and NH4+ in wastewater. [ABSTRACT FROM AUTHOR]

A new landfill cover system, biochar-methanotrophs-clay (BMC) cover is recommended for reducing methane emissions at landfills. It also contributes to decreasing soil permeability and improving soil water retention in a long time, due to highly porous structure of biochar and the growth metabolism of methanotrophs. To determine the effects of biochar content, oxidation aging times and methane-filled days on hydraulic properties, a total of 60 groups of experiments were conducted. The saturated hydraulic conductivity (ksat) was obtained by flexible wall permeameter with controllable hydraulic head pressure. The results showed that the ksat of BMC increased with increasing biochar content and oxidation aging times, while decreased with adding methane-filled days. The soil-water characteristic curves (SWCCs) were obtained with soil suction measured by the filter paper method. The results indicated the water retention capacity of MBC reduced with increasing oxidation aging times but increased with adding methane-filled days. Detected by mercury intrusion porosimetry (MIP), fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), the differences displayed the changes of pore structures and extracellular polymeric substances (EPS). The oxidation aging of biochar increased the volume of pores, resulting in the increased ksat and the decreased water retention capacity. However, the growing of methanotrophs decreased the volume of pores, resulting in the ksat decreased and the water retention capacity increased due to EPS. No matter how many times the oxidation aging process was experienced, the BMC with longer methane-filled days exhibited relatively lower ksat and better water retention capacity. This implied a more stable barrier capacity to reduce water infiltration in the long term. By combing a series of macro and micro experiments, this paper provides theoretical guidance for the application of biocharmethanotroph- clay mixture to landfill covers. [ABSTRACT FROM AUTHOR]

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