Methanotrophic Communities and Cultivation of Methanotrophs from Rice Paddy Fields Fertilized with Pig-livestock Biogas Digestive Effluent and Synthetic Fertilizer in the Vietnamese Mekong Delta.

Biogas digestive effluent (BDE) has been applied to rice fields in the Vietnamese Mekong Delta (VMD). However, limited information is available on the community composition and isolation of methanotrophs in these fields. Therefore, the present study aimed (i) to clarify the responses of the methanotrophic community in paddy fields fertilized with BDE or synthetic fertilizer (SF) and (ii) to isolate methanotrophs from these fields. Methanotrophic communities were detected in rhizospheric soil at the rice ripening stage throughout 2 cropping seasons, winter-spring (dry) and summer-autumn (wet). Methanotrophs were isolated from dry-season soil samples. Although the continued application of BDE markedly reduced net methane oxidation potential and the copy number of pmoA genes, a dissimilarity ordination ana-lysis revealed no significant difference in the methanotrophic community between BDE and SF fields (P=0.167). Eleven methanotrophic genera were identified in the methanotrophic community, and Methylosinus and Methylomicrobium were the most abundant, accounting for 32.3-36.7 and 45.7-47.3%, respectively. Type-I methanotrophs (69.4-73.7%) were more abundant than type-II methanotrophs (26.3-30.6%). Six methanotrophic strains belonging to 3 genera were successfully isolated, which included type I (Methylococcus sp. strain BE1 and Methylococcus sp. strain SF3) and type II (Methylocystis sp. strain BE2, Methylosinus sp. strain SF1, Methylosinus sp. strain SF2, and Methylosinus sp. strain SF4). This is the first study to examine the methanotrophic community structure in and isolate several methanotrophic strains from BDE-fertilized fields in VMD.

A Patent Landscape on Methane Oxidizing Bacteria (MOB) or Methanotrophs.

Methane-oxidizing bacteria (MOB) or methanotrophs are a category of bacteria that rely on methane as their primary carbon and energy source. Methane is the second most abundant greenhouse gas after carbon dioxide and is comparatively far more potent in trapping heat in the atmosphere. MOBs are important microorganisms in the global carbon cycle where they play a crucial role in the oxidation of methane. The present review provides a comprehensive patent landscape on technology development using MOB. The first patent in this technology domain was recorded in 1971, with a notable surge in activity observed in 2020. A detailed patent analysis revealed that the early inventions were mainly focused on the production of various metabolites and bioremediation using MOB. In the later years, patents were filed in the area of identification of various species of MOB and their large-scale production. From 2010 onwards, consistent patent filing was observed in the genetic engineering of MOB to enhance their methane oxidizing capacity. The United States and China have emerged as the global leaders in terms of patent filing in this technology space. Precigen Inc. and Exxon Research Engineering Co., US were the top patent assignees followed by the University of Tsinghua and Calysta Inc. The Highest number of patent applications have claimed metabolite production by using MOB followed by their use in bioremediation. Methylosinus has emerged as the predominant microorganism of choice for methane oxidation applications.

[Research progress in bioconversion of C1 gases into oleochemicals].

The utilization of C1 gases (CH4, CO2, and CO) for the production of oleochemicals applied in the energy and platform chemicals through microbial engineering has emerged as a promising approach to reduce greenhouse gas emissions and decrease dependence on fossil fuel. C1 gas-utilizing microorganisms, such as methanotrophs, microalgae, and acetogens, are capable of converting C1 gases as the sole substrates for cell growth and oleochemical synthesis with different carbon-chain lengths, garnering considerable attention from both scientific community and industry field for sustainable biomanufacturing. This paper comprehensively reviews recent advancements in the development of engineered cell factories utilizing C1 gases for the production of oleochemicals, elucidating the key metabolic pathways of biosynthesis. Furthermore, this paper highlights the research progress and prospects in optimizing gene expression, metabolic pathway reconstruction, and fermentation conditions for efficient oleochemical production from C1 gases. This review provides valuable insights and guidance for the efficient utilization of C1 gases and the development of carbon cycling-based bioeconomy.

Sustainable production of C50 carotenoid bacterioruberin from methane using soil-enriched microbial consortia.

Bacterioruberin is widely used in medicine, food, and cosmetics owing to its prominent characteristics of antioxidants and bioactivities. Bioconversion of methane into bacterioruberin is a promising way to address biomanufacturing substrate costs and greenhouse gas emissions but has not been achieved yet. Herein, this study aimed to upcycle methane to bacterioruberin by microbial consortia. The microbial consortia consist of Methylomonas and Methylophilus capable of synthesizing carotenoids from methane was firstly enriched from paddy soil. Through this microbial community, methane was successfully converted into C50 bacterioruberin for the first time. The bioconversion process was then optimized by the response surface methodology. Finally, the methane-derived bacterioruberin reached a record yield of 280.88 ± 2.94 µg/g dry cell weight. This study presents a cost-effective and eco-friendly approach for producing long-chain carotenoids from methane, offering a significant advancement in the direct conversion of greenhouse gases into value-added products.

Treatment of Anaerobic Digester Liquids via Membrane Biofilm Reactors: Simultaneous Aerobic Methanotrophy and Nitrogen Removal.

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.

Polyhydroxyalkanoate Production by Methanotrophs: Recent Updates and Perspectives.

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.

Methane-oxidizing bacterial community dynamics in sub-alpine forest soil.

Microbial activities in sub-alpine forest soil influence global cycling of the potent greenhouse gas methane. Understanding the dynamics of methane-oxidizing bacterial communities, particularly the roles of potentially active versus total microbial populations, is necessary for reducing uncertainty in global methane budget estimates. However, our understanding of the factors influencing methane cycling in forest soils is limited by our lack of knowledge about the biology of the microbes involved and how these communities are shaped by their environment. Here, we compared the composition and potential activity of microbial communities using 16S rRNA gene amplicon sequencing of total genomic DNA (gDNA) and potentially active complementary DNA (cDNA) from shallow soil in Red Butte Canyon (Salt Lake City, Utah, USA). We compared riparian and upland soils at two time points in the growing season and found distinct differences in both the community composition of the gDNA and cDNA libraries and the potential drivers of these community structures. Aerobic methane-oxidizing bacteria (methanotrophs) were detected in all samples, with cDNA libraries containing a higher average relative abundance and diversity of methanotrophs compared to gDNA libraries. Methane flux at the sample sites did not significantly correlate to the relative abundance (gDNA) or potential activity (cDNA) of methanotrophs. In the cDNA libraries, there were significant positive correlations between the abundance of Methylococcaceae family methanotrophs and several non-methanotrophic methylotrophs previously found to be associated with methane-oxidizing bacterial communities. These findings suggest a complex relationship between methane-cycling bacterial communities and methane flux and highlight the need for further in situ studies to understand the environmental and ecological influences of these microbial consortia. IMPORTANCE: Methane-oxidizing bacteria are found in diverse soil and sediment environments and play an important role in mitigating flux of this potent greenhouse gas into the atmosphere. However, it is unclear how these bacteria and their associated communities are structured in the environment and how their activity ultimately influences methane flux. In this work, we examine the composition and structure of methane-oxidizing bacterial communities in sub-alpine forest soil and find soil- and time-specific differences between the stable and potentially active populations. We also find that the potentially active populations of certain methanotrophs and non-methanotrophs are positively correlated. This work provides a step toward refining our understanding of microbially mediated biogeochemical cycles.

Exploring modes of microbial interactions with implications for methane cycling.

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.

Quantitative assessment of methane bioconversion based on kinetics and bioenergetics.

The biological conversion of methane under ambient conditions can be performed by methanotrophs that utilize methane as both a sole source of energy and a carbon source. However, compared to the established microbial chassis used for general fermentation with sugar as a feedstock, the productivity of methanotrophs is low. The fundamental knowledge of their metabolic or cellular bottlenecks is limited. In this review, the industrial-scale potential of methane bioconversion was evaluated. In particular, the enzyme kinetics associated with the oxidation and assimilation of methane were investigated to evaluate the potential of methane fermentation. The kinetics of enzymes involved in methane metabolism were compared with those used in the metabolic processes of traditional fermentation (glycolysis). Through this analysis, the current limitations of methane metabolism were identified. Methods for increasing the efficiency of methane bioconversion and directions for the industrial application of methane-based fermentation were discussed.

Role of methanogenesis and methanotrophy in CH4 fluxes from rice paddies under elevated CO2 concentration and elevated temperature.

The differential responses of methanogenesis and methanotrophy to elevated carbon dioxide concentrations ([CO2]) (e[CO2]) and elevated temperature ([T]) (e[T]) may lead to dramatic changes in the response of CH4 emissions from rice paddies to global warming. In this study, we systematically investigated the responses and mechanisms of CH4 flux from rice paddies to e[CO2] and e[T] based on the production and oxidation of CH4. The CH4 flux, soil properties, and soil methanogenesis and methanotrophy were observed under CK (ambient [CO2] + ambient [T]), EC (e[CO2] by 200 µmol mol-1 + ambient [T]), ET (ambient [CO2] + e[T] by 2 °C), and ECT (e[CO2] by 200 µmol mol-1 + e[T] by 2 °C) treatments. The results revealed that EC, ET, and ECT significantly increased the cumulative amount of CH4 (CAC) in the rice paddies by 10.63, 15.20, and 11.77 kg ha-1, respectively, compared with CK. ECT increased the CAC in the rice paddies by 1.14 kg ha-1 compared with EC. Moreover, EC, ET, and ECT significantly enhanced the methane production potential (MPP) and methane oxidation potential (MOP) and tended to increase the mcrA gene abundance of the methanogens. EC tended to prompt the pmoA gene abundance of the methanotrophs, but the effect of ET on the pmoA gene abundance was less consistent across the growth stages. ECT significantly decreased the relative abundances of Methanosarcina and Methylocystis (Type II) by 4.9 % and 14.2 %, respectively, while it increased the relative abundance of Methylosarcina (Type I) by 24.0 % compared with CK. Overall, the increased MPP/MOP, mcrA/pmoA, and microbial biomass carbon under climate change increased the CH4 flux from the rice paddies. The contribution of e[CO2] to the CH4 flux was significantly enhanced by e[T], which could further exacerbate the risk of global climate change induced by e[CO2].

Exploring optimal incubation conditions and characteristics of methane oxidizing organisms in deep-sea environments.

Anaerobic methanotrophic archaea (ANME) play key roles in buffering the methane budget in the deep-sea environment. This study aimed to explore the optimal environmental conditions for ANME enrichment. The result showed that the sample at 10.5 MPa contained the largest copy numbers of methyl-coenzyme M reductase alpha subunit (mcrA) gene (1.1 × 106 copies/g) compared to any other pressures and the sample at 4 °C contained higher mcrA gene (1.6 × 106 copies/g) than other temperatures. The optimal enrichment pressure for ANME-2c is 10.5 MPa at 4 °C, with an optimal subsequent incubation for ANME-2c less than 211days. Moreover, the beta nearest taxon index was significantly correlated with the incubation time (P<0.05). Total inorganic carbon and sulfate ion were key environmental factors driving community construction. This study offers insights into how ANME-2c was enriched and how species coexist in shared habitats during enrichment.

Optimization of methane gas-liquid mass transfer during biogas-based ectoine production in bubble column bioreactors.

Nowadays, the utilization of biogas for energy generation is hindered by the declining production costs of solar and wind power. A shift towards the valorization of biogas into ectoine, a highly valuable bioproduct priced at 1000 €â¸±kg-1, offers a novel approach to fostering a more competitive biogas market while contributing to carbon neutrality. This study evaluated the optimization of CH4 gas-liquid mass transfer in 10 L bubble column bioreactors for CH4 conversion into ectoine and hydroxyectoine using a mixed methanotrophic culture. The influence of the empty bed residence time (EBRTs of 27, 54, and 104 min) at different membrane diffuser pore sizes (0.3 and 0.6 mm) was investigated. Despite achieving CH4 elimination capacities (CH4-ECs) of 10-12 g⸱m-3⸱h-1, an EBRT of 104 min mediated CH4 limitation within the cultivation broth, resulting in a negligible biomass growth. Reducing the EBRT to 54 min entailed CH4-ECs of 21-24 g⸱m-3⸱h-1, concomitant to a significant increase in biomass growth (up to 0.17 g⸱L⸱d-1) and reaching maximum ectoine and hydroxyectoine accumulation of 79 and 13 mg⸱gVSS-1, respectively. Conversely, process operation at an EBRT of 27 min lead to microbial inhibition, resulting in a reduced biomass growth of 0.09 g⸱L⸱d-1 and an ectoine content of 47 mg⸱gVSS-1. While the influence of diffuser pore size was less pronounced compared to EBRT, the optimal process performance was observed with a diffuser pore size of 0.6 mm.

Selective Enrichment of Methylococcaceae versus Methylocystaceae Methanotrophs via Control of Methane Feeding Schemes.

Methanotrophs are crucial in keeping environmental CH4 emissions in check. However, the contributions of different groups of methanotrophs at terrestrial CH4-oxidation hotspots, such as the oxic-anoxic interface of rice paddies, have shown considerable inconsistency across observations. To address the knowledge gap regarding this inconsistency, methanotrophic microbiomes were enriched from paddy soils in well-mixed CH4-fed batch reactors under six different incubation conditions, prepared as combinations of two CH4 mixing ratios (0.5 and 10%) and three supplemented Cu2+ concentrations (0, 2, and 10 µM). Monitoring of temporal community shifts in these cultures revealed a dominance of Methylocystis spp. in all 0.5%-CH4 cultures, while methanotrophs affiliated to Gammaproteobacteria dominated the 10%-CH4 cultures that were less consistent both temporally and across conditions. The shotgun metagenome analyses of the 0.5%-CH4 cultures corroborated the Methylocystis dominance and, interestingly, showed that copper deficiency did not select for mmoXYZ-possessing methanotrophs. Instead, a mbn cluster, accounting for approximately 5% of the Methylocystis population, was identified, suggesting the ecological significance of methanobactin in Cu-deficient methanotrophy. These findings underscore the important role of Methylocystis spp. in mitigating emissions from terrestrial CH4 hotspots and suggest the feasibility of directed enrichment and/or isolation of Methylocystis spp. for utilization in, for example, methanobactin and polyhydroxybutyrate production.

Methane-Driven Perchlorate Reduction by a Microbial Consortium.

The phenomenon of methane oxidation linked to perchlorate reduction has been reported in multiple studies; yet, the underlying microbial mechanisms remain unclear. Here, we enriched suspended cultures by performing methane-driven perchlorate reduction under oxygen-limiting conditions in a membrane bioreactor (MBR). Batch test results proved that perchlorate reduction was coupled to methane oxidation, in which acetate was predicted as the potential intermediate and oxygen played an essential role in activating methane. By combining DNA-based stable isotope probing incubation and high-throughput sequencing analyses of 16S rRNA gene and functional genes (pmoA, pcrA, and narG), we found that synergistic interactions between aerobic methanotrophs (Methylococcus and Methylocystis) and perchlorate-reducing bacteria (PRB; Denitratisoma and Dechloromonas) played active roles in mediating methane-driven perchlorate reduction. This partnership was further demonstrated by coculture experiments in which the aerobic methanotroph could produce acetate to support PRB to complete perchlorate reduction. Our findings advance the understanding of the methane-driven perchlorate reduction process and have implications for similar microbial consortia linking methane and chlorine biogeochemical cycles in natural environments.

Biotransformation of PFAA Precursors by Oxygenase-Expressing Bacteria in AFFF-Impacted Groundwater and in Pure-Compound Studies with 6:2 FTS and EtFOSE.

Numerous US drinking water aquifers have been contaminated with per- and polyfluoroalkyl substances (PFAS) from fire-fighting and fire-training activities using aqueous film-forming foam (AFFF). These sites often contain other organic compounds, such as fuel hydrocarbons and methane, which may serve as primary substrates for cometabolic (i.e., nongrowth-linked) biotransformation reactions. This work investigates the abilities of AFFF site relevant bacteria (methanotrophs, propanotrophs, octane, pentane, isobutane, toluene, and ammonia oxidizers), known to express oxygenase enzymes when degrading their primary substrates, to biotransform perfluoroalkyl acid (PFAA) precursors to terminal PFAAs. Microcosms containing AFFF-impacted groundwater, 6:2 fluorotelomer sulfonate (6:2 FTS), or N-ethylperfluorooctane sulfonamidoethanol (EtFOSE) were inoculated with the aerobic cultures above and incubated for 4 and 8 weeks at 22 °C. Bottles were sacrificed, extracted, and subjected to target, nontarget, and suspect screening for PFAS. The PFAA precursors 6:2 FTS, N-sulfopropyldimethyl ammoniopropyl perfluorohexane sulfonamide (SPrAmPr-FHxSA), and EtFOSE transformed up to 99, 71, and 93%, respectively, and relevant daughter products, such as the 6:1 fluorotelomer ketone sulfonate (6:1 FTKS), were identified in quantities previously not observed, implicating oxygenase enzymes. This is the first report of a suite of site relevant PFAA precursors being transformed in AFFF-impacted groundwater by bacteria grown on substrates known to induce specific oxygenase enzymes. The data provide crucial insights into the microbial transformation of these compounds in the subsurface.

Methane-cycling microbial communities from Amazon floodplains and upland forests respond differently to simulated climate change scenarios.

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.

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.

The challenge of estimating global termite methane emissions.

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.

Uncovering the microbial community structure and physiological profiles of terrestrial mud volcanoes: A comprehensive metagenomic insight towards their trichloroethylene biodegradation potentiality.

Mud volcanoes are dynamic geological features releasing methane (CH4), carbon dioxide (CO2), and hydrocarbons, harboring diverse methane and hydrocarbon-degrading microbes. However, the potential application of these microbial communities in chlorinated hydrocarbons bioremediation purposes such as trichloroethylene (TCE) has not yet been explored. Hence, this study investigated the mud volcano's microbial diversity functional potentiality in TCE degradation as well as their eco-physiological profiling using metabolic activity. Geochemical analysis of the mud volcano samples revealed variations in pH, temperature, and oxidation-reduction potential, indicating diverse environmental conditions. The Biolog Ecoplate™ carbon substrates utilization pattern showed that the Tween 80 was highly consumed by mud volcanic microbial community. Similarly, MicroResp® analysis results demonstrated that presence of additive C-substrates condition might enhanced the cellular respiration process within mud-volcanic microbial community. Full-length 16 S rRNA sequencing identified Proteobacteria as the dominant phylum, with genera like Pseudomonas and Hydrogenophaga associated with chloroalkane degradation, and methanotrophic bacteria such as Methylomicrobium and Methylophaga linked to methane oxidation. Functional analysis uncovered diverse metabolic functions, including sulfur and methane metabolism and hydrocarbon degradation, with specific genes involved in methane oxidation and sulfur metabolism. These findings provide insights into the microbial diversity and metabolic capabilities of mud volcano ecosystems, which could facilitate their effective application in the bioremediation of chlorinated compounds.

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.