Methanotrophic Microorganisms Research Articles

An upcycling bioprocess for sustainable aviation fuel production from food waste-derived greenhouse gases: Life cycle assessment and techno-economic analysis

Biogas generated from food waste through anaerobic digestion is typically utilized for heat and electricity. However, recent developments in synthetic biology have enabled the conversion of carbon dioxide (CO2) and methane (CH4) in biogas into desired products by microorganisms. This study introduced a novel bioroute for the production of sustainable aviation fuel (SAF) using food waste in a carbon–neutral and cost-effective manner. Both CO2 and CH4 derived from food waste are sequentially bioconverted into lipids by photosynthetic and methanotrophic microorganisms, which are then upgraded into SAF. A comparative life cycle assessment was conducted, revealing that this proposed bioroute has a lower environmental impact than a thermo-route involving hydrothermal liquefaction. Furthermore, a techno-economic analysis of the bioroute was also performed to evaluate both the capital and operating costs, showcasing the feasibility of this concept with current cutting-edge technologies. With potential food waste disposal subsidies taken into consideration, the bioroute-based SAF could yield an internal rate of return of up to 38%, demonstrating its economic viability in the market. By leveraging food waste and innovative biotechnology, this bioroute has the potential to contribute to a more eco-friendly and economically sustainable aviation industry.

Recent advances in methanol production from methanotrophs.

Methanol, the simplest aliphatic molecule of the alcohol family, finds diverse range of applications as an industrial solvent, a precursor for producing other chemicals (e.g., dimethyl ether, acetic acid and formaldehyde), and a potential fuel. There are conventional chemical routes for methanol production such as, steam reforming of natural gas to form syngas, followed by catalytic conversion into methanol; direct catalytic oxidation of methane, or hydrogenation of carbon dioxide. However, these chemical routes are limited by the requirement for expensive catalysts and extreme process conditions, and plausible environmental implications. Alternatively, methanotrophic microorganisms are being explored as biological alternative for methanol production, under milder process conditions, bypassing the requirement for chemical catalysts, and without imposing any adverse environmental impact. Methanotrophs possess inherent metabolic pathways for methanol production via biological methane oxidation or carbon dioxide reduction, thus offering a surplus advantage pertaining to the sequestration of two major greenhouse gases. This review sheds light on the recent advances in methanotrophic methanol production including metabolic pathways, feedstocks, metabolic engineering, and bioprocess engineering approaches. Furthermore, various reactor configurations are discussed in view of the challenges associated with solubility and mass transfer limitations in methanotrophic gas fermentation systems.

Salinity causes differences in stratigraphic methane sources and sinks

Methane metabolism, driven by methanogenic and methanotrophic microorganisms, plays a pivotal role in the carbon cycle. As seawater intrusion and soil salinization rise due to global environmental shifts, understanding how salinity affects methane emissions, especially in deep strata, becomes imperative. Yet, insights into stratigraphic methane release under varying salinity conditions remain sparse. Here we investigate the effects of salinity on methane metabolism across terrestrial and coastal strata (15–40 m depth) through in situ and microcosm simulation studies. Coastal strata, exhibiting a salinity level five times greater than terrestrial strata, manifested a 12.05% decrease in total methane production, but a staggering 687.34% surge in methane oxidation, culminating in 146.31% diminished methane emissions. Salinity emerged as a significant factor shaping the methane-metabolizing microbial community's dynamics, impacting the methanogenic archaeal, methanotrophic archaeal, and methanotrophic bacterial communities by 16.53%, 27.25%, and 22.94%, respectively. Furthermore, microbial interactions influenced strata system methane metabolism. Metabolic pathway analyses suggested Atribacteria JS1's potential role in organic matter decomposition, facilitating methane production via Methanofastidiosales. This study thus offers a comprehensive lens to comprehend stratigraphic methane emission dynamics and the overarching factors modulating them.

Thermophilic methane oxidation is widespread in Aotearoa-New Zealand geothermal fields.

Geothermal areas represent substantial point sources for greenhouse gas emissions such as methane. While it is known that methanotrophic microorganisms act as a biofilter, decreasing the efflux of methane in most soils to the atmosphere, the diversity and the extent to which methane is consumed by thermophilic microorganisms in geothermal ecosystems has not been widely explored. To determine the extent of biologically mediated methane oxidation at elevated temperatures, we set up 57 microcosms using soils from 14 Aotearoa-New Zealand geothermal fields and show that moderately thermophilic (>40°C) and thermophilic (>60°C) methane oxidation is common across the region. Methane oxidation was detected in 54% (n = 31) of the geothermal soil microcosms tested at temperatures up to 75°C (pH 1.5-8.1), with oxidation rates ranging from 0.5 to 17.4 μmol g-1 d-1 wet weight. The abundance of known aerobic methanotrophs (up to 60.7% Methylacidiphilum and 11.2% Methylothermus) and putative anaerobic methanotrophs (up to 76.7% Bathyarchaeota) provides some explanation for the rapid rates of methane oxidation observed in microcosms. However, not all methane oxidation was attributable to known taxa; in some methane-consuming microcosms we detected methanotroph taxa in conditions outside of their known temperature range for growth, and in other examples, we observed methane oxidation in the absence of known methanotrophs through 16S rRNA gene sequencing. Both of these observations suggest unidentified methane oxidizing microorganisms or undescribed methanotrophic syntrophic associations may also be present. Subsequent enrichment cultures from microcosms yielded communities not predicted by the original diversity studies and showed rates inconsistent with microcosms (≤24.5 μmol d-1), highlighting difficulties in culturing representative thermophilic methanotrophs. Finally, to determine the active methane oxidation processes, we attempted to elucidate metabolic pathways from two enrichment cultures actively oxidizing methane using metatranscriptomics. The most highly expressed genes in both enrichments (methane monooxygenases, methanol dehydrogenases and PqqA precursor peptides) were related to methanotrophs from Methylococcaceae, Methylocystaceae and Methylothermaceae. This is the first example of using metatranscriptomics to investigate methanotrophs from geothermal environments and gives insight into the metabolic pathways involved in thermophilic methanotrophy.

Production of Bacillus subtillis protein mass on the microbial mass of Methylococcus capsulatus

The growing demand for food of animal origin has contributed to the annual increase in the agricultural population of productive animals in the world, which in turn has led to a significant shortage of feeds and an increase in their cost. Therefore, the purpose of this research was to explore the qualitative composition of feed products obtained by culturing methanotrophic microorganisms Methylococcus capsulatus with probiotic bacteria Bacillus subtillis. Arbitrage methods for determining the quality of feeds, which are regulated by regulatory documents (ISO), were used in the research. The results of the research demonstrate that the protein product obtained by growing Methylococcus capsulatus culture has a high content of “crude” protein at the level of 60.9%, which corresponds to high-protein feeds of animal origin by its technical characteristics. The addition of probiotic microorganisms Bacillus subtillis to the medium for cultivation significantly improved the qualitative parameters of the synthesised protein by increasing by 1.5% the amount of essential amino acids, increasing by 3.8% fatty acids and increasing the concentration of calcium and phosphorus. The increase in the concentration of lysine, isoleucine, valine and asparagic acid, due to the cocultivation of two microorganisms allowed increasing their nutritional value for cattle since these amino acids are the most demanded in ruminant diets when using corn silage and other plant feeds. The addition of Bacillus subtillis culture allowed reducing the content of “crude” fibre and improving its biological characteristics by changing the microbiological composition of the obtained product. In the future, the biotechnological method of obtaining feed protein for animals will reduce the dependence of animal breeding on the cultivation of fodder crops and weather conditions

The formation of authigenic phosphorus minerals in cold-seep sediments from the South China Sea: Implications for carbon cycling below the sulfate-methane transition

The formation of authigenic phosphorus (P) minerals near the sulfate-methane transition (SMT) represents an important pathway of P burial in marine sediments. However, our current understanding of the coupling between the formation of authigenic phosphate and carbon and iron (Fe) cycling is insufficient. In this study, a piston core recovered from the Haima cold seeps of the Qiongdongnan basin, northern South China Sea, was used to analyze pore-water parameters and solid-phase Fe and P speciation. Results from a previous study indicate that the current SMT is located at approximately 1 m below the seafloor (mbsf) and a fossil SMT located at approximately 6.5 mbsf. Dissolved phosphate concentrations and solid-phase iron oxide (FeOx) contents are found to decrease with depth, while Fe-bound P (PFe) and authigenic phosphate (PAuth) contents increase with depth in the zone between the current and fossil SMTs where gas hydrate is present, suggesting that vivianite and authigenic apatite formed in this zone. Gas hydrate below the current SMT will dissociate once methane is undersaturated, which could persistently provide dissolved methane to prevent the downward shift of the current SMT where methane is continually consumed. Such a methane-rich environment maintained by gas hydrate may favor the persistent reduction of FeOx and the formation of vivianite. Dissolved phosphate concentrations are high, but decrease rapidly with depth at the fossil SMT. Combined with higher FeOx and PAuth contents and lower PFe contents and lower POrg/total organic carbon (TOC) ratios, these results suggest the formation of authigenic apatite at the fossil SMT. The high dissolved phosphate concentration and low POrg/TOC ratios at the fossil SMT are interpreted to reflect preferential release of P during the degradation of organic matter generated by methanotrophic microorganisms. Overall, our study shows that P speciation in methane-rich sediments provides insight into the formation processes of authigenic P minerals near the SMT and associated carbon and Fe cycling processes.

CAGE13-7 Cruise Report: Gas Release Activity & Underwater Landslide Research Cruise

The overall aim of the CAGE 13-7 cruise was to study the gas release activity from gas hydrated sub-seabed environments at the continental margin off Svalbard towards the Norwegian-Greenland Sea and Arctic Ocean. Acoustic measurements in the water column, water sampling for gas analyses, seismic profiling, bathymetry mapping, and sediment coring allowed to reach this aim. Generally, the water column above gas flares may be rich in methane but methanotrophic microorganisms might hinder an escape of methane from the water to the atmosphere. At the Molloy transform and the Vestnesa ridge we collected seismic data and sediment cores for sampling gas hydrates. We also took sediment cores from a submarine slide complex at the continental margin of NW Svalbard. The age of this slide is of interest because it sits on gas hydrated sediments as indicated by a BSR. The timing of the slope failure is unknown. At the massive Hinlopen slide area we surveyed the eastern sidewall, the toe of the slope and a block within the major slide debris flow area to understand better a potential coupling between slide processes and gas hydrates. Seismic profiles show bottom simulating reflectors that are indicative for gas hydrate underneath the southeastern headwall of this slide complex.
 The cruise may be known as: CAGE13_JM

Geochemistry of organic matter by multi-proxy analyses and temperature sensitivity of methanogenesis in clearwater Amazonian lake sediments

Despite the relevance of bottom sediments from clearwater floodplain lakes in organic matter preservation and degradation, there is a scarcity of data regarding the composition of molecular biomarkers and responses of benthic methanogenesis in Amazonian lakes in global warming scenarios. Here, surface sediments from a small clearwater floodplain lake (Jacundá Lake) in the Brazilian Amazon (Tapajós River) were assessed in a combined approach between molecular biomarker composition and the sensitivity of methanogenesis under two experimental temperatures: 25 °C as control vs. + 4 °C as an Intergovernmental Panel on Climate Change (IPCC) global warming scenario for 2081–2100. Lipid biomarker composition (n-alkanes, sterols) in a 12-cm sediment core revealed a strong predominance of terrestrial-derived organic matter over aquatic contributions, indicating more refractory preserved organic matter, while aquatic organic matter represents substrates to biological degradation. Moreover, alkanoic acids and microbial triterpenoids indicated an intense microbial contribution and elevated organic matter processing. Compound specific isotopic analysis confirmed the presence of methanotrophic microorganisms (diploptene δ13C = −53.5‰) and an uptake of depleted 13C in aquatic organic matter. Diagenetic transformation of biomarkers also indicated a highly anoxic depositional environment throughout the core. Methanogenesis in the upper 15-cm sediment layer under 25 °C (39.3 mg C–CH4 m−2 d−1) was similar to higher rates reported in Amazonian lakes and increased about 60% in the treatment when the temperature increased by 4 °C. Despite the predominant terrestrial sources and subsequent refractory composition of organic matter, our findings integrating biomarkers and metabolic processes support that biomass stocks in clearwater lake sediments of the Amazon basin may be sensitive to global warming.

Coupling methanotrophic denitrification to anammox in a moving bed biofilm reactor for nitrogen removal under hypoxic conditions

Simultaneous removal of ammonium and nitrate was achieved in a methane-fed moving bed biofilm reactor (MBBR). In the reactor, methanotrophic microorganisms oxidized methane under hypoxic conditions likely to methanol, hence providing an electron donor to denitrifiers to reduce nitrate to nitrite that then allowed anaerobic ammonium oxidizing bacteria (Anammox) to remove excess ammonium as N2. The ammonium and nitrate removal rates reached 72.09 ± 5.81 mgNH4+–N/L/d and 62.61 ± 4.17 mgNO3−–N/L/d when the MBBR was operated in continuous mode. Nitrate removal by the methane-fed mixed consortia was confirmed in a batch test revealing a CH4/NO3− molar removal ratio of 1.15. The functional populations were unveiled by FISH analysis and 16S rRNA gene sequencing, which showed that the biofilm was dominated by Anammox bacteria (Candidatus Kuenenia) and diverse taxa associated with the capacity for denitrification: aerobic methanotrophs (Methylobacter, Methylomonas, and unclassified Methylococcaceae), methylotrophic denitrifiers (Opitutaceae and Methylophilaceae), and other heterotrophic denitrifiers (Ignavibacteriaceae, Anaerolineaceae, Comamonadaceae, Rhodocyclaceae and Thauera). Neither DAMO archaea nor DAMO bacteria were found in the sequencing analysis, indicating that more unknown community members possess the metabolic capacity of methanotrophic denitrification.

Multiple Groups of Methanotrophic Bacteria Mediate Methane Oxidation in Anoxic Lake Sediments.

Freshwater lakes represent an important source of the potent greenhouse gas methane (CH4) to the atmosphere. Methane emissions are regulated to large parts by aerobic (MOx) and anaerobic (AOM) oxidation of methane, which are important CH4 sinks in lakes. In contrast to marine benthic environments, our knowledge about the modes of AOM and the related methanotrophic microorganisms in anoxic lake sediments is still rudimentary. Here, we demonstrate the occurrence of AOM in the anoxic sediments of Lake Sempach (Switzerland), with maximum in situ AOM rates observed within the surface sediment layers in presence of multiple groups of methanotrophic bacteria and various oxidants known to support AOM. However, substrate-amended incubations (with NO2−, NO3−, SO42−, Fe-, and Mn-oxides) revealed that none of the electron acceptors previously reported to support AOM enhanced methane turnover in Lake Sempach sediments under anoxic conditions. In contrast, the addition of oxygen to the anoxic sediments resulted in an approximately 10-fold increase in methane oxidation relative to the anoxic incubations. Phylogenetic and isotopic evidence indicate that both Type I and Type II aerobic methanotrophs were growing on methane under both oxic and anoxic conditions, although methane assimilation rates were an order of magnitude higher under oxic conditions. While the anaerobic electron acceptor responsible for AOM could not be identified, these findings expand our understanding of the metabolic versatility of canonically aerobic methanotrophs under anoxic conditions, with important implications for future investigations to identify methane oxidation processes. Bacterial AOM by facultative aerobic methane oxidizers might be of much larger environmental significance in reducing methane emissions than previously thought.

Increased soil moisture intensifies the impacts of forest-to-pasture conversion on methane emissions and methane-cycling communities in the Eastern Amazon

Climatic changes are altering precipitation patterns in the Amazon and may influence soil methane (CH4) fluxes due to the differential responses of methanogenic and methanotrophic microorganisms. However, it remains unclear if these climate feedbacks can amplify land-use-related impacts on the CH4 cycle. To better predict the responses of soil CH4-cycling microorganisms and emissions under altered moisture levels in the Eastern Brazilian Amazon, we performed a 30-day microcosm experiment manipulating the moisture content (original moisture; 60%, 80%, and 100% of field capacity - FC) of forest and pasture soils. Gas samples were collected periodically for gas chromatography analysis, and methanogenic archaeal and methanotrophic bacterial communities were assessed using quantitative PCR and metagenomics. Positive and negative daily CH4 fluxes were observed for forest and pasture, indicating that these soils can act as both CH4 sources and sinks. Cumulative emissions and the abundance of methanogenesis-related genes and taxonomic groups were affected by land use, moisture, and their interaction. Pasture soils at 100% FC had the highest abundance of methanogens and CH4 emissions, 22 times higher than forest soils under the same treatment. Higher ratios of methanogens to methanotrophs were found in pasture than in forest soils, even at field capacity conditions. Land use and moisture were significant factors influencing the composition of methanogenic and methanotrophic communities. The diversity and evenness of methanogens did not change throughout the experiment. In contrast, methanotrophs exhibited the highest diversity and evenness in pasture soils at 100% FC. Taken together, our results suggest that increased moisture exacerbates soil CH4 emissions and microbial responses driven by land-use change in the Amazon. This is the first report on the microbial CH4 cycle in Amazonian upland soils that combined one-month gas measurements with advanced molecular methods.

Разнообразие психрофильных бактерий и их биотехнологический потенциал (обзор)

Psychrophilic bacteria are a large group of microorganisms that prevail in low-temperature ecosystems. Psychrophilic bacteria have undergone a number of adaptations that help them exist in such conditions. One of such adaptations is the use of enzymes with a high specific activity at low temperatures. Such enzymes are usually called “cold-active.” These enzymes have potential applications in biotechnology and industry. In our review, we considered individual genera of psychrophilic bacteria, current global trends in the study of cold-active enzymes, their applications, and place in industrial biotechnology. Thus, the main goal of this study was to explore the diversity of psychrophilic bacteria, as well as opportunities of their application in biotechnology. The natural ecological sites of psychrophiles are numerous and varied. Psychrophiles form a permanent microflora of eternal cold regions, polar regions and oceans. Bacteria belonging to this group are found in soil, water or associated with plants and animals. An important site for psychrophilic microorganisms is a low-temperature water reservoir. At present, many new genera of psychrophiles and psychrotrophs have been derived from the bottom sediments and sea waters of the Arctic and Antarctic and described. Psychrophilic microorganisms are found in caves and in ancient ice crystal structures. The latter testifies to the very possibility of the super-long anabiosis phenomenon, as well as vital capacity preservation without division for a long period of time. Psychrophiles do not have a single form, they belong to at least several phylogenetic groups. Psychrophilic forms are found among the representatives of a large number of genera. There are no common physiological and biochemical parameters typical of psychrophilic bacteria. They comprise rods, cocci, vibrios, gram-negative and gram-positive bacteria, bacteria that produce and do not produce spores, strict aerobes, facultative and strict anaerobes. We lay greater emphasis on the diversity of psychrophilic bacteria capable of producing industrially important enzymes. The review considers bacteria belonging to the genera Vibrio and Aliivibrio, Pseudomonas, Achromobacter, Arthrobacter, Pseudoalteromonas, Bacillus, Clostridium, Micrococcus, Psychrobacter, Psychromonas, Flavobacterium, and psychrophilic methanotrophic microorganisms. These bacteria enzymes are used in agriculture, biotechnology, pharmaceuticals and household chemicals, as well as other sectors of the national economy. Psychrophilic bacteria produce a chemical compound that can be used in medicine. For example, Pseudomonas antarctica contains a cluster of genes encoding microcin B, R-type pyocins, adenosylcobalamin, and pyrroloquinoline quinone. Thus, P. antarctica has antibiotic activity. Psychrobacter proteolyticus also has an antineoplastic action and secrets an extracellular cold-adapted metalloproteinase being able to inhibit the space-occupying process. Cold-active metalloproteinases are also widely used as detergents, in currying, food sector and molecular biology. The immunogenic Pal conformable protein was derived from the psychrophilic strain of The representatives of the genus Arthrobacter capable of metabolizing diuron and petroleum products have an important property. A. agilis produces a red pigment, a bacterioruberin-type carotenoid being interesting as an antioxidant. A. psychrochitiniphilus is promising for cleaning water areas, oil-polluted coastlines, as it decomposes oil and petroleum products. Flavobacterium limicola is a potential source of cold-active protease. This bacterium is characterized by an increase in protease secretion as temperature decreases. Thus, F. limicola can be used in environmental biotransformations and bioremediations. The psychrophilic bacteria of the genus Bacillus are the participants of active studies. Their cold-active enzymes have a high potential in various areas of biomedicine, immunology, decontamination, and various industrial applications. The antifreeze proteins of psychrophilic Clostridia are considered a promising biotechnological product for use in medicine, food, beauty products, fuel, and other industries. This study reviews literary sources and indicates that at present obligate and facultative psychrophiles (psychrotrophs) and their cold-active enzymes are of scientific interest throughout the world. A significant part of the research is focused on a general understanding of the distribution of psychrophilic bacteria and a local study of enzymatic activity. A further study of psychrophilic microorganisms producing enzymes at low temperatures will reveal new ways for the development of biotechnologies in various sectors of the national economy. The paper contains 94 References. The Authors declare no conflict of interest.

Detection of methanotrophic microorganisms in sludge and sediment samples from sewage treatment systems

Abstract This study investigated various groups of methanotrophic microorganisms, including the anaerobic methane-oxidizing archaea (ANME) group, aerobic methanotrophic bacteria, and bacteria of the phylum NC10 (Candidatus Methylomirabilis oxyfera). The polymerase chain reaction (PCR) technique was employed with specific primers for the pmoA gene from the aerobic methanotrophic and M. Oxyfera methanotrophic denitrifying (NC10 phylum) and for the anaerobic methanotrophic archaea 16S rRNA gene (ANME-1 and ANME-2). Sludge and sediment samples were analyzed from different sewage treatment systems installed at the Sanitation Research and Training Center (CePTS) at the Arrudas wastewater treatment plant (Arrudas WWTP), in Belo Horizonte, Brazil. ANME was shown to be present in sludges from the upflow anaerobic sludge blanket (UASB) reactor and activated sludge system, and in sediments from the polishing pond and wetlands. On the other hand, aerobic methanotrophic bacteria were detected only in the polishing pond samples, while no methanotrophic denitrifiers of the M. oxyfera genre were detected at all. Besides investigating and detecting different groups of methanotrophs in the treatment systems, the study provided support for another in which samples from the systems analyzed were selected for use as inoculum for methane anaerobic oxidation potential experiments and methanotrophic microorganism enrichment.

Microbial activity, methane production, and carbon storage in Early Holocene North Sea peats

Abstract. Northern latitude peatlands act as important carbon sources and sinks, but little is known about the greenhouse gas (GHG) budgets of peatlands that were submerged beneath the North Sea during the last glacial–interglacial transition. We found that whilst peat formation was diachronous, commencing between 13 680 and 8360 calibrated years before the present, stratigraphic layering and local vegetation succession were consistent across a large study area. Large carbon stores were measured. In situ methane (CH4) concentrations of sediment pore waters were widespread but low at most sites, with the exception of two locations. Incubation experiments in the laboratory revealed molecular signatures of methanogenic archaea, with strong increases in rates of activity upon methylated substrate amendment. Remarkably, methanotrophic activity and the respective diagnostic molecular signatures could not be detected. Heterotrophic Bathyarchaeota dominated the archaeal communities, and bacterial populations were dominated by candidate phylum JS1 bacteria. In the absence of active methanogenic microorganisms, we conclude that these sediment harbour low concentrations of widespread millennia-old CH4. The presence of large widespread stores of carbon and in situ methanogenic microorganisms, in the absence of methanotrophic microorganisms, holds the potential for microbial CH4 production if catalysed by a change in environmental conditions.

Microbial Involvement in Carbon Transformation via CH4 and CO2 in Saline Sedimentary Pool.

Simple SummaryMethane and carbon dioxide are commonly found in the environment and are considered the most important greenhouse gases. Transformation of these gases is in large carried by microorganisms, which occur even in extreme environments. This study presents methane-related biological processes in saline sediments of the Miocene Wieliczka Formation, Poland. Biological activity (carbon dioxide and methane production or methane oxidation), confirmed by stable isotope indices, occurred in all of the studied Wieliczka rocks. CH4-utilizing microbes constituted 0.7–3.6% while methanogens (represented by Methanobacterium) only 0.01–0.5% of taxa present in the Wieliczka Salt Mine rocks. Water activity was the key factor regulating microbial activity in saline subsurface sediments. Generally, CO2 respiration was higher in anaerobic conditions while methanogenic and methanotrophic activities were dependent on the type of rock.Methane and carbon dioxide are one of the most important greenhouse gases and significant components of the carbon cycle. Biogeochemical methane transformation may occur even in the extreme conditions of deep subsurface ecosystems. This study presents methane-related biological processes in saline sediments of the Miocene Wieliczka Formation, Poland. Rock samples (W2, W3, and W4) differed in lithology (clayey salt with veins of fibrous salt and lenses of gypsum and anhydrite; siltstone and sandstone; siltstone with veins of fibrous salt and lenses of anhydrite) and the accompanying salt type (spiza salts or green salt). Microbial communities present in the Miocene strata were studied using activity measurements and high throughput sequencing. Biological activity (i.e., carbon dioxide and methane production or methane oxidation) occurred in all of the studied clayey salt and siltstone samples but mainly under water-saturated conditions. Microcosm studies performed at elevated moisture created more convenient conditions for the activity of both methanogenic and methanotrophic microorganisms than the intact sediments. This points to the fact that water activity is an important factor regulating microbial activity in saline subsurface sediments. Generally, respiration was higher in anaerobic conditions and ranged from 36 ± 2 (W2200%t.w.c) to 48 ± 4 (W3200%t.w.c) nmol CO2 gdw−1 day−1. Methanogenic activity was the highest in siltstone and sandstone (W3, 0.025 ± 0.018 nmol CH4 gdw−1 day−1), while aerobic methanotrophic activity was the highest in siltstone with salt and anhydrite (W4, 220 ± 66 nmol CH4 gdw−1 day−1). The relative abundance of CH4-utilizing microorganisms (Methylomicrobium, Methylomonas, Methylocystis) constituted 0.7–3.6% of all taxa. Methanogens were represented by Methanobacterium (0.01–0.5%). The methane-related microbes were accompanied by a significant number of unclassified microorganisms (3–64%) and those of the Bacillus genus (4.5–91%). The stable isotope composition of the CO2 and CH4 trapped in the sediments suggests that methane oxidation could have influenced δ13CCH4, especially in W3 and W4.

Water Table Fluctuation and Methane Emission in Pineapples (Ananas comosus (L.) Merr.) Cultivated on a Tropical Peatland

Inappropriate drainage and agricultural development on tropical peatland may lead to an increase in methane (CH4) emission, thus expediting the rate of global warming and climate change. It was hypothesized that water table fluctuation affects CH4 emission in pineapple cultivation on tropical peat soils. The objectives of this study were to: (i) quantify CH4 emission from a tropical peat soil cultivated with pineapple and (ii) determine the effects of water table depth on CH4 emission from a peat soil under simulated water table fluctuation. Soil CH4 emissions from an open field pineapple cultivation system and field lysimeters were determined using the closed chamber method. High-density polyethylene field lysimeters were set up to simulate the natural condition of cultivated drained peat soils under different water table fluctuations. The soil CH4 flux was measured at five time intervals to obtain a 24 h CH4 emission in the dry and wet seasons during low- and high-water tables. Soil CH4 emissions from open field pineapple cultivation were significantly lower compared with field lysimeters under simulated water table fluctuation. Soil CH4 emissions throughout the dry and wet seasons irrespective of water table fluctuation were not affected by soil temperature but emissions were influenced by the balance between methanogenic and methanotrophic microorganisms controlling CH4 production and consumption, CH4 transportation through molecular diffusion via peat pore spaces, and non-microbial CH4 production in peat soils. Findings from the study suggest that water table fluctuation at the soil–water interface relatively controls the soil CH4 emission from lysimeters under simulated low- and high-water table fluctuation. The findings of this study provide an understanding of the effects of water table fluctuation on CH4 emission in a tropical peatland cultivated with pineapple.

Methane-dependent selenate reduction by a bacterial consortium.

Methanotrophic microorganisms play a critical role in controlling the flux of methane from natural sediments into the atmosphere. Methanotrophs have been shown to couple the oxidation of methane to the reduction of diverse electron acceptors (e.g., oxygen, sulfate, nitrate, and metal oxides), either independently or in consortia with other microbial partners. Although several studies have reported the phenomenon of methane oxidation linked to selenate reduction, neither the microorganisms involved nor the underlying trophic interaction has been clearly identified. Here, we provide the first detailed evidence for interspecies electron transfer between bacterial populations in a bioreactor community where the reduction of selenate is linked to methane oxidation. Metagenomic and metaproteomic analyses of the community revealed a novel species of Methylocystis as the most abundant methanotroph, which actively expressed proteins for oxygen-dependentmethane oxidation and fermentation pathways, but lacked the genetic potential for selenate reduction. Pseudoxanthomonas, Piscinibacter, and Rhodocyclaceae populations appeared to be responsible for the observed selenate reduction using proteins initially annotated as periplasmic nitrate reductases, with fermentation by-products released by the methanotrophs as electron donors. The ability for the annotated nitrate reductases to reduce selenate was confirmed by gene knockout studies in an isolate of Pseudoxanthomonas. Overall, this study provides novel insights into the metabolic flexibility of the aerobic methanotrophs that likely allows them to thrive across natural oxygen gradients, and highlights the potential role for similar microbial consortia in linking methane and other biogeochemical cycles in environments where oxygen is limited.

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

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

Not just a methane source: Amazonian floodplain sediments harbour a high diversity of methanotrophs with different metabolic capabilities.

The Amazonian floodplain forests are dynamic ecosystems of great importance for the regional hydrological and biogeochemical cycles and function as a significant CH4 source contributing to the global carbon balance. Unique geochemical factors may drive the microbial community composition and, consequently, affect CH4 emissions across floodplain areas. Here, we report the in situ composition of CH4 cycling microbial communities in Amazonian floodplain sediments. We considered how abiotic factors may affect the microbial community composition and, more specifically, CH4 cycling groups. We collected sediment samples during wet and dry seasons from three different types of floodplain forests, along with upland forest soil samples, from the Eastern Amazon, Brazil. We used high-resolution sequencing of archaeal and bacterial 16S rRNA genes combined with real-time PCR to quantify Archaea and Bacteria, as well as key functional genes indicative of the presence of methanogenic (mcrA) and methanotrophic (pmoA) microorganisms. Methanogens were found to be present in high abundance in floodplain sediments, and they seem to resist the dramatic environmental changes between flooded and nonflooded conditions. Methanotrophs known to use different pathways to oxidise CH4 were detected, including anaerobic archaeal and bacterial taxa, indicating that a wide metabolic diversity may be harboured in this highly variable environment. The floodplain environmental variability, which is affected by the river origin, drives not only the sediment chemistry but also the composition of the microbial communities. These environmental changes seem also to affect the pools of methanotrophs occupying distinct niches. Understanding these shifts in the methanotrophic communities could improve our comprehension of the CH4 emissions in the region.

Development of Ice Cover in Water Areas during Methane

In traditional hydrometeorology and ice physics, when analyzing the development of ice, only degree-days of frost are taken into account. Despite the presence of pores in the ice formed during inhomogeneous crystallization and dynamic loads, ice is universally considered monolithic. Situations where ice cannot withstand design loads in frosty conditions are academically inexplicable, although it is common knowledge, for example, porous ice in reeds. Proof of methane accumulations under the ice-fountains of fire over holes in swampy waters. “Culprit” is methane. Methanotrophic microorganisms, structurally and functionally specialize in using it as a source of carbon and energy, and turn monolithic ice into porous, practically without changing its thickness. When rushing, dark products of methanotrophy and detritus raised by gas bubbles appear on the surface of the ice. The albedo of the ice surface decreases, contributing to its melting and the formation of dilutions. The early melting of ice in dilutions and their transformation into vast wormwood is due to methanotrophy products and seismogenic small detritus, which gravitationally slowly settling out of the cold photic layer, thinning it, contributes to an additional insolation warm-up of 2°C ÷ 3°C, freeing the waters from ice months earlier than normal.