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Methane seepages are widespread in the Black Sea. However, microbiological research has been carried out only at the continental shelf seeps. The present work dealt with coastal gas seepages of the Kalamit Bay (Black Sea). High-throughput 16S rRNA gene sequencing and radiotracer analysis (14С and 35S) were used to determine the composition of the microbial community and the rates of microbial sulfate reduction and methane oxidation. The phylum Proteobacteria, represented mainly by sulfate reducers of the class Deltaproteobacteria, was the predominant in sequence dataset. Bacteroidetes and Planctomycetes were other numerous phyla. Among archaea, the phylum Woesearchaeota and Marine Benthic Group B were predominant in the upper horizons. Relative abundance of Euryarchaeota of the families Methanomicrobiaceae and Methanosarcinaceae (including ANME-3 archaea) increased in deeper sediment layers. Sulfate reduction rate (up to 2.9 mmol/L × day) was considerably higher than the rate of anaerobic methane oxidation (up to 43.4 μmol/L × day), which indicated insignificant contribution of anaerobic methane oxidation to the total sulfide production.

Hydroasoustic techniques were used for detection and mapping of gas jet areas in the coastal regions of the Crimean peninsula. Gas seep areas in the bays Laspi, Khersones, and Kazach'ya were chosen for detailed microbiological investigation. The first type of gas jets, observed in the Laspi Bay, was probably associated with discarge of deep thermogenic methane along the faults. Methane isotopic composition was char- acterized by Δ13C of -35.3 degrees. While elevated rates of aerobic methane oxidation were revealed in the sandy sediments adjacent to the methane release site, no evidence of bacterial mats was found. The second type of gas emission, observed in the Khersones Bay, was accompanied by formation of bacterial biofilms of the "Thiodendron" microbial community type, predominated by filamentous, spirochete-like organisms, in the areas of gas seepage. The isotopic composition of methane was there considerably lower (-60.4 degrees), indicating a considerable contribution of modern microbial methane to the gas bubbles discharged in this bay. Activity of the third type of gas emission, the seeps of the Kazach'ya Bay, probably depended directly on modern microbial processes of organic matter degradation in the upper sediment layers. The rates of sulfate reduction and methanogenesis were 260 and 34 μmol dm(-3) day(-1), respectively. Our results indicate different mechanisms responsible for formation of methane jets in the Laspi Bay and in the coastal areas of the Heracles Peninsula, where the bays Kazach'ya and Khersones are located.

Aerobic methane oxidation has been mostly studied in environments with moderate to low temperatures. However, the process also occurs in terrestrial thermal springs, where little research on the subject has been done to date. The potential activity of methane oxidation and diversity of aerobic methanotrophic bacteria were studied in sediments of thermal springs with various chemical and physical properties, sampled across the Kunashir Island, the Kuriles archipelago. Activity was measured by means of the radioisotope tracer technique utilizing (14)C-labeled methane. Biodiversity assessments were based on the particulate methane monooxygenase (pmoA) gene, which is found in all known thermophilic and thermotolerant methanotrophs. We demonstrated the possibility of methane oxidation in springs with temperature exceeding 74 °C, and the most intensive methane uptake was shown in springs with temperatures about 46 °C. PmoA was detected in 19 out of 30 springs investigated and the number of pmoA gene copies varied between 10(4) and 10(6) copies per ml of sediment. Phylogenetic analysis of PmoA sequences revealed the presence of methanotrophs from both the Alpha- and Gammaproteobacteria. Our results suggest that methanotrophs inhabiting thermal springs with temperature exceeding 50 °C may represent novel thermophilic and thermotolerant species of the genera Methylocystis and Methylothermus, as well as previously undescribed Gammaproteobacteria.

The rates of microbial processes of sulfate reduction and of the methane cycle were measured in the bottom sediments of the Sevastopol basin, where seeps of gaseous methane have been previously found. Typically for marine environments, sulfate reduction played the major role in the terminal phase of decomposition of organic matter (OM) in reduced sediments of this area. The rate of this process depended on the amount of available OM. The rate of methanogenesis in the sediments increased with depth, peaking in the subsurface horizons, where decreased sulfate concentration was detected in the pore water. The highest rates of sulfate-dependent anaerobic methane oxidation were found close to the methane-sulfate transition zone as is typical of most investigated marine sediments. The data on the carbon isotopic composition of gaseous methane from the seeps and dissolved CH4 from the bottom sediments, as well as on the rates of microbial methanogenesis and methane oxidation indicate that the activity of the methane seeps results from accumulation of biogenic methane in the cavities of the underlying geological structures with subsequent periodic release of methane bubbles into the water column.

Comprehensive microbiological and biogeochemical investigation of a pockmark within one of the sites of gas-saturated sediments in the Gdansk depression, Baltic Sea was carried out during the 87th voyage of the Professor Shtokman research vessel. Methane content in the near-bottom water and in the underlying sediments indicates stable methane flow from the sediment into the water. In the 10-m water layer above the pockmark, apart from methane anomalies, elevated numbers of microorganisms and enhanced rates of dark CO2 fixation (up to 1.15 micromol C/(1 day)) and methane oxidation (up to 2.14 nmol CH4/(1 day)) were revealed. Lightened isotopic composition of suspended organic matter also indicates high activity of the near-bottom microbial community. Compared to the background stations, methane content in pockmark sediments increased sharply from the surface to 40-60 ml/dm3 in the 20-30cm horizon. High rates of bacterial sulfate reduction (SR) were detected throughout the core (0-40 cm); the maximum of 74 micromol/(dm3 day) was located in subsurface horizons (15-20 cm). The highest rates of anaerobic methane oxidation (AMO), up to 80 micromol/(dm3 day), were detected in the same horizon. Good coincidence of the AMO and SR profiles with stoichiometry close to 1:1 is evidence in favor of a close relation between these processes performed by a consortium of methanotrophic archaea and sulfate-reducing bacteria. Methane isotopic composition in subsurface sediments of the pockmark (from -53.0 to -56.5% per hundred) does not rule out the presence of methane other than the biogenic methane from the deep horizons of the sedimentary cover.

The biogeochemical and molecular biological study of the chemocline and sediments of saline meromictic lakes Shira and Shunet (Khakass Republic, Russia) was performed. A marked increase in the rates of sulfate reduction and methanogenesis was revealed at the medium depths of the chemocline. The rates of these processes in the bottom sediments decreased with depth. The numbers of Bacteria, Archaea, and of sulfate-reducing bacteria (SRB) were determined by fluorescence in situ hybridization with rRNA specific oligonucleotide probes labeled with horseradish peroxidase and subsequent tyramide signal amplification. In the chemocline, both the total microbial numbers and those of Bacteria were shown to increase with depth. The archaea and SRB were present in almost equal numbers. In the lake sediments, a drastic decrease in microbial numbers with depth was revealed. SRB were found to prevail in the upper sediment layer and archaea in the lower one. This finding correlates with the measured rates of sulfate reduction and methanogenesis.

A detailed study of the processes of anaerobic methane oxidation and sulfate reduction in the bacterial mats occurring on coral-like carbonate structures in the region of methane seeps in the Black Sea, as well as of the phenotypic diversity of sulfate-reducing bacteria developing in this zone, has been performed. The use of the radioisotopic method shows the microbial mat structure to be heterogeneous. The peak activity of the two processes was revealed when a mixture of the upper (dark) and underlying (intensely pink) layers was introduced into an incubation flask, which confirms the suggestion that methanotrophic archaea and sulfate-reducing bacteria closely interact in the process of anaerobic methane oxidation. Direct correlation between the rate of anaerobic methane oxidation and the methane and electron acceptor concentrations in the medium has been experimentally demonstrated. Several enrichment and two pure cultures of sulfate-reducing bacteria have been obtained from the near-bottom water and bacterial mats. Both strains were found to completely oxidize the substrates to CO2 and H2S. The bacteria grow at temperatures ranging from -1 to 18 (24) degrees C, with an optimum in the 10-18 degrees C range, and require the presence of 1.5-2.5% NaCl and 0.07-0.2% MgCl2 x 6H2O. Regarding the aggregate of their phenotypic characteristics (cell morphology, spectrum of growth substrates, the capacity for complete oxidation), the microorganisms isolated have no analogues among the psychrophilic sulfate-reducing bacteria already described. The results obtained demonstrate the wide distribution of psychrophilic sulfate-reducing bacteria in the near-bottom water and bacterial mats covering the coral-like carbonate structures occurring in the region of methane seeps in the Black Sea, as well as the considerable catabolic potential of this physiological group of psychrophilic anaerobes in deep-sea habitats.

Methane emission from the following types of tundra soils was studied: coarse humic gleyey loamy cryo soil, peaty gley soil, and peaty gleyey midloamy cryo soil of the arctic tundra. All the soils studied were found to be potential sources of atmospheric methane. The highest values of methane emission were recorded in August at a soil temperature of 8-10 degrees C. Flooded parcels were the sources of atmospheric methane throughout the observation period. The rates of methane production and oxidation in tundra soils of various types at 5 and 15 degrees C were studied by the radioisotope method. Methane oxidation was found to occur in bog water, in the green part of peat moss, and in all the soil horizons studied. Methane formation was recorded in the horizons of peat, in clay with plant roots, and in peaty moss dust of the bogey parcels. At both temperatures, the methane oxidation rate exceeded the rate of methane formation in all the horizons of the mossy-lichen tundra and of the bumpy sinkhole complex. Methanogenesis prevailed only in a sedge-peat moss bog at 15 degrees C. Enrichment bacterial cultures oxidizing methane at 5 and 15 degrees C were obtained. Different types of methanotrophic bacteria were shown to be responsible for methane oxidation under these conditions. A representative of type I methylotrophs oxidized methane at 5 degrees C, and Methylocella tundrae, a psychroactive representative of an acidophilic methanotrophic genus Methylocella, at 15 degrees C.

Microbiological and biogeochemical investigations of the processes of methane production (MP) and methane oxidation (MO) in the coastal waters and littoral of the Kandalaksha Bay of the White Sea were carried out. The studies were conducted in the coastal zones and in the water areas of the Kandalaksha Preserve, Moscow University White Sea Biological Station, and Zoological Institute (RAS) Biological Station in August, 1999, 2000, and 2001 and in March, 2001. The rate of CO2 assimilation in the shallow and littoral sediments was 35-27800 microg C/(dm3 day) in summer and 32.8-88.9 microg C/(dm3 day) in winter. The maximal rates of MP were observed in the littoral sediments in the zone of macrophyte decomposition, in local depressions, and in the estuary of a freshwater creak (up to 113 microl/(dm3 day)). The maximal level of MO was observed in the shallow estuarine sediments (up to 2450 microl/(dm3 day)). During the winter season, at the temperature of -0.5 to 0.5 degrees C, the MP rate in the littoral sediments was 0.02-0.3 microl/(dm3 day), while MO rate was 0.06-0.7 microl/(dm3 day). The isotopic data obtained indicate that the C(org) of the mats and of the upper sediment layers is enriched with the heavy 13C isotope by 1-4 per thousand as compared to the C(org) of the suspension, comprised on 33.5-34.3% of phytoplankton. A striking difference was found between the levels of methane emission by the typical littoral microlanscapes. In fine sediments, the average emission was 675 microl CH4/(m2 day), in the stormy discharge stretch sediments it was 1670 microl CH4/(m2 day), and under the stones and in silted pits, 1370 microl CH4/(m2 day). The calculation performed with consideration of the microlandscape areas with a high production allowed the CH4 production of 1 km2 of the littoral to be estimated as 192-300 1 CH4/(km2 day).

Seasonal investigations of methane distribution and rates of its oxidation and generation in the water column and sediments of the Black Sea northwestern shelf were carried out within the framework of the interdisciplinary projects "European River-Ocean Systems" (EROS-2000, EROS-21) and "Biogenic Gases Exchange in the Black Sea" (BigBlack) in August 1995, May 1997, and December 1999. Experiments that involved the addition of 14CH3COONa and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 559 mumol/(m2 day)) were found in coastal sediments in summer time. In winter and spring, methane production in the same sediments did not exceed 3.6-4.2 mumol/(m2 day). The delta 13C values of methane ranged from -70.7 to -81.8@1000, demonstrating its microbial origin and contradicting the concept of the migration of methane from cold seeps or from the oil fields located at the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of methane (from 6.8 to 320 mumol/(m2 day)) arrives in the atmosphere.

The aragonite constructions of the Black Sea are formed in a stable anaerobic zone and are a perfect object to study the natural mechanism of anaerobic methane oxidation. The most probable pathway of methane oxidation is its methanogen-mediated reaction with bicarbonates, dissolved in seawater, with the formation of water and acetate, which is then consumed by other components of the anaerobic community. Comparison of the delta 13C values of carbonate minerals and organic matter once more demonstrated that the formation of the organic matter of biomass is accompanied by intense fractionation of carbon isotopes, as a result of which the total organic matter of biomass acquires an extremely light isotopic composition, characterized by delta 13C values as low as -83.8@1000.

Rates of carbon dioxide assimilation and methane oxidation were determined in various zones of the Rainbow Hydrothermal Field (36 degrees N) of the Mid-Atlantic Ridge. In the plume above the hydrothermal field, anomalously high methane content was recorded; the microbial population density (up to 10(5) cells/ml) was an order of magnitude higher than the background values; and the CO2 assimilation rate varied from 0.01 to 1.1 micrograms C/(1 day). Based on the data on CO2 assimilation, the production of organic carbon due to bacterial chemosynthesis in the plume was calculated to be 930 kg/day or 340 tons/year (about 29% of the organic carbon production in the photic zone). In the black smoke above active smokers, the microbial population density was as high as 10(6) cells/ml; the rate of CO2 assimilation made up 5-10 micrograms C/(1 day); the methane oxidation rate varied from 0.15 to 12.7 mu/(1 day); and the methane concentration ranged from 1.05 to 70.6 mu/l. In bottom sediments enriched with sulfides, the rate of CO2 assimilation was at least an order of magnitude higher than in oxidized metal-bearing sediments. At the base of an active construction site, whitish sediment was found, which was characterized by a methane high content (92 mu/dm3) and a high rate of oxidation (1.7 mu/(dm3 day)).

Seasonal cyanobacterial blooms have a negative impact on freshwater ecosystems. The role of cyanobacteria in methane production and their relationship with methanogenic archaea are not yet well understood. The goal of the present work was to identify the features of methanogenesis in the water column and sediments of a profundal part of the freshwater Lake Senezh (Moscow oblast) during a period of cyanobacterial over-bloom. Analytical, radiotracer, microscopic, molecular biological, and incubation techniques were used. Alkalization and oxygen oversaturation of the 0‒2-m water layer were caused by intensive photosynthesis. The near-bottom water (4 m) was pH-neutral and hypoxic; the sediments were reduced. Methane was detected throughout the water column; its concentration in the surface water was an order of magnitude lower than in the near-bottom water and 4 orders of magnitude lower than in the sediments. Cyanobacteria of the species Microcystisaeruginosa predominated in the photic zone (up to 30% of the total number of the 16S rRNA gene fragments). The sequences of cyanobacteria and freshwater members of the SAR11 clade, which can potentially be involved in aerobic methanogenesis via decomposition of methylphosphonates (MPn), were also detected. The sequences of hydrogenotrophic methanogens of the genus Methanoregula, which are potentially capable of methanogenesis in cooperation with cyanobacteria, were revealed in oxygen-supersaturated water. Hydrogenotrophic and acetoclastic pathways of methanogenesis predominated in reduced sediments. Sequences of methanogens of the orders Methanomicrobiales, Methanobacteriales, Methanosarciniales, and Methanomassiliicoccales were detected there. Cyanobacterial bloom promoted methanogenesis both in the photic zone of Lake Senezh (due to MPn decomposition and anaerobic methanogenesis in association with cyanobacterial aggregates) and in the near-bottom water and sediments (due to oxygen depletion and excessive release of substrates caused by sedimentation and degradation of cyanobacterial mortmass). [ABSTRACT FROM AUTHOR]

Eutrophication of lakes results in the intensification of anaerobic processes, including methanogenesis, and therefore in enhanced emission of methane. A littoral area with its variable oxygen regime is the first to react to eutrophication. The diversity of microbial communities in littoral areas is insufficiently studied, and little data are available concerning the methane cycle microorganisms. In this work, the methanogenesis and methane oxidation were investigated in the littoral site of a freshwater temperate Lake Senezh (Russia). A combination of analytical, microbiological and molecular techniques was used, including physicochemical analyses, high-throughput sequencing, potential activity measurements, and cultivation on selective media. The littoral site was found to be an extremely labile ecological niche, which harbors a diverse community containing aerobic, facultative anaerobic and anaerobic microorganisms, both autotrophs and heterotrophs, which may perform all reactions of the N, S, and CH4 cycles. Methane formation was carried out via hydrogenotrophic, acetoclastic, methylotrophic, and methyl-reducing pathways. Among methanotrophs, type I organisms predominated; type II, nitrate- and nitrite-dependent methanotrophs were also revealed. Comparison of the average rates of methanogenesis and aerobic methane oxidation suggests that all methane, which may potentially be formed in the littoral site of the lake, could simultaneously be oxidized. [ABSTRACT FROM AUTHOR]

The technology of single-cell protein production from natural gas is based on using thermotolerant methanotrophic bacteria with high growth rates on methane. So far, the spectrum of strains used for industrial purposes was restricted to members of the genus Methylococcus. This poses limitations to further development of this technology and fuels the search for new cultures of fast-growing methanotrophs. The later task was addressed in the present work by analyzing the sediment samples of the Chernaya River, Crimea. Molecular analysis of the microbial community composition in the sediment revealed Gammaproteobacteria as the predominant group (33‒42% of all retrieved 16S rRNA gene fragments), as well as Chloroflexi, Actinobacteria, Alphaproteobacteria, Bacteroidota, and Acidobacteria as other numerically significant community members. The methanotrophic enrichment culture obtained from the sediment contained bacteria of the genus Methylomonas as the major component, with the relative abundance of up to 60% of all 16S rRNA gene fragments. The use of various strategies for methanotroph isolation resulted in obtaining three isolates of target bacteria of the genera Methylomonas, Methylomagnum and Methylocystis. The optimal growth temperatures of these isolates were 25, 35, and 40°С, respectively. The highest specific growth rate in batch culture, 0.21 h−1, was determined for Methylocystis sp. Kr9, which displayed 99.22 and 99.13% 16S rRNA gene sequence similarity to the type strains of two Methylocystis species, Methylocystis echinoides IMET 10491T and Methylocystis parvus OBBPT, respectively. [ABSTRACT FROM AUTHOR]

The taxonomic diversity and metabolic activity of microbial communities in the Laptev Sea water column above and outside the methane seep field were studied. The concentrations of dissolved methane in the water column at both stations were comparable until the depth of the pycnocline (25 m). At this depth, local methane maxima were recorded, with the highest concentration (116 nM CH4) found at the station outside the methane seep field. Results of the 16S rRNA gene sequencing and measurements of the rates of hydrogenotrophic methanogenesis indicated the absence of methanogenesis caused by the methanogenic archaea in the pycnocline and in other horizons of the water column. The 16S rRNA-based analysis of microbial phylogenetic diversity, as well as radiotracer analysis of the rates of primary production (PP), dark CO2 assimilation (DCA), and methane oxidation (MO), indicated the functioning of a diverse community of pelagic microorganisms capable of transforming a wide range of organic compounds under oligotrophic conditions of the Arctic basin. Hydrochemical prerequisites and possible microbial agents of aerobic methane production via demethylation of methylphosphonate and decomposition of dimethylsulfoniopropionate using dissolved organic matter synthesized in the PP, DCA, and MO processes are discussed. [ABSTRACT FROM AUTHOR]

The major substrates for methanogenesis were used for investigation of cultured methanogenic archaea from coastal methane seeps near the Tarkhankut Peninsula, Black Sea. Analysis of the 16S rRNA gene sequences revealed that growth of the classical methanogenic Euryarchaeota occurred in all enrichments but was absent in the controls without the substrates. Enrichments from the seep differed in microbial composition from those from the background point. The most numerous archaea belonged to the genera Methanolobus (medium with methanol and hydrogen), Methanosarcina (trimethylamine and hydrogen), Methanococcoides (trimethylamine), and Methanococcus (hydrogen and CO2). Syntrophic growth of hydrogenotrophic archaea of the genus Methanogenium with clostridia and members of the family Thermotogaceae probably occurred in enrichments with acetate. Relatively low similarity of the recovered 16S rRNA gene sequences with the closest cultured relatives (94% and lower) indicated that the Methanogenium phylotype belonged to a new species. The same was true for the Methanosarcina phylotype revealed in the culture with trimethylamine and hydrogen (97% and less similarity of the 16S rRNA gene sequences to those of the closest cultured relatives). [ABSTRACT FROM AUTHOR]

Thermokarst lakes are formed as a result of thawing of ice-rich permafrost, causing development of land depressions which in flat areas are filled with water in the case of positive water balance. Activation of the thermokarst process is one of the possible indicators of permafrost degradation under the conditions of global warming. Thermokarst lakes occur in the areas of continuous, discontinuous, and sporadic permafrost, i.e., in Siberia, Alaska, Canada, and northern Scandinavia. Specific microbial communities adapted to long-term exposure to low temperatures develop in such lakes. They vary in the rates of aerobic and anaerobic metabolism depending on the mineral composition of bottom sediments, availability of organic matter, limnological and hydrological features of the lakes. High rates of methane emission are characteristic of a number of thermokarst lakes. Recent studies of thermokarst lakes revealed active methane formation via various methanogenic pathways, as well as aerobic and anaerobic methane oxidation by diverse methanogenic and methanotrophic bacteria and archaea. The question of what mechanisms and microorganisms are involved in anaerobic methane oxidation, which may be responsible for up to 80% of methane consumption in thermokarst lakes, remains, however, open. The microorganisms actively functioning beneath the ice during the long winter season, while highly important for northern aquatic ecosystems, also remain insufficiently studied. Almost no serious microbiological research on thermokarst lakes has been carried out in Russia, although permafrost occupies up to 65% of its territory, thermokarst process is common, and thermokarst lakes are numerous. [ABSTRACT FROM AUTHOR]

Abstract: A seasonal study of microbial methane oxidation (MO) and sulfate reduction (SR) processes in bottom sediments was carried out at five stations in the estuarian Sevastopol coastal area, which differed in their sedimentation and geochemical conditions. High methane concentrations in bottom sediments, as well as accordingly high MO rates, were obtained at stations marked by high organic carbon (Corg) concentrations. The dependence of these values was found to be exponential, whereas for SR, the amount of organic carbon was not the limiting factor. For the studied stations, the integral SR rates ranged from 2.9 to 11.3 mmol m-2 day-1. The trends of the SR rate have opposite directions for the open and closed parts of the sea: SR decreased during study period at the center of the bay, while in the open sea area it increased. The MO rates varied in a wide range from 0.0001 to 3.6 mmol m-2 day-1; the highest were obtained in Corg-rich sediments of the central part of the bay. Only at one station, where the mean annual Corg content in sediments reached 3.39%, did the methane concentration in sediment pore water exceed the calculated solubility. [ABSTRACT FROM AUTHOR]

Geochemical, biogeochemical, and molecular genetic investigation of the upper (0-5 cm) bottom sediments of the Yamal sector of the Kara Sea was carried out. The Yamal sector is well-protected from the massive inflow of river water. The sediments were oxidized at the surface and weakly reduced in the 3−5-cm layer. Corg content varied from 0.1 to 1.3%, while the level of dissolved СН4 was 1.9 to 20.3 μmol L-1. The isotopic composition of organic matter (OM) carbon, δ13Corg, varied from-27.5 to-22.2‰ (-25.4‰ on average). The share of terrigenous OM was 13.3 to 72.2% (48.9% on average). The rate of methane production, methane oxidation, and sulfate reduction varied from 0.8 to 9.0 (2.7 on average) nmol СН4 dm-3 day-1, from 9.9 to 103 (31.6 on average) nmol СН4 dm-3 day-1, and from 0.49 to 2.2 (1.1 on average) μmol S dm-3 day-1, respectively. High-throughput sequencing of the amplicons of the 16S rRNA genes was used to reveal the physiological groups of microorganisms responsible for the processes of methane production and oxidation, sulfate reduction, and oxidation of reduced sulfur compounds. Members of the phylum Woesearchaeota were predominant among archaea. Methanogenic archaea belonged to the families Methanobacteriaceae, Methanococcaceae, and Methanosarcinaceae (Euryarchaeota). Methanotrophs of the family Methylococcaceae were revealed among the Gammaproteobacteria, with their share in the sediments ~1%. In the class Deltaproteobacteria (15.4%), three orders of sulfate reducers were predominant: Desulfobacterales, Desulfovibrionales, and Desulfuromonadales. Oxidation of reduced sulfur compounds was carried out by chemolithoautotrophic bacteria of the genera Sulfurovum, Sulfurimonas, and Arcobacter of the class Epsilonproteobacteria (1.1% of the total microbial number). [ABSTRACT FROM AUTHOR]

The review deals with systematization and generalization of new information concerning the phylogenetic and functional diversity of prokaryotes involved in the methane cycle. Methane is mostly produced by methanogenic archaea, which are responsible for the terminal stage of organic matter decomposition in a number of anoxic ecotopes. Although phylogeny, physiology, and biochemistry of methanogens have been extensively studied, important discoveries were made recently. Thus, members of deep phylogenetic lineages within the Euryarchaeota phylum ( Methanomassiliicoccales, ' Candidatus Methanofastidiosa,' ' Methanonatronarchaeia') and even outside it (' Ca. Verstraetearchaeota' and ' Ca. Bathyarchaeota') were reported to carry out methyl-reducing methanogenesis. Moreover, evidence was obtained on aerobic methane production by marine heterotrophic bacteria, which demethylate polysaccharide esters of methylphosphonic acid. Methanotrophic microorganisms oxidize methane both aerobically and anaerobically, decreasing significantly the release of this greenhouse gas into the atmosphere. In the presence of oxygen methane is oxidized by methanotrophic members of Alpha- and Gammaproteobacteria, as well as by Verrucomicrobia. Methanotrophic gammaproteobacteria have been recently revealed in hypoxic and even anoxic environments, where they probably oxidize methane either in a trophic consortium with oxygenic phototrophs and/or methylotrophs or using electron acceptors other than oxygen. Anaerobic methane oxidation has been known for a long time. Sulfat- and nitrate-dependent anaerobic methane oxidation carried out by the ANME archaea via reverse methanogenesis are the best studied processes. While metal-dependent anaerobic methane oxidation is considered possible, the mechanisms and agents responsible for this process have not been reliably identified. Intracellular oxygen production during nitrite-dependent anaerobic methane oxidation was shown for bacteria ' Ca. Methylomirabilis oxyfera.' These findings stimulate interest in the processes and microorganisms of the methane cycle. [ABSTRACT FROM AUTHOR]

Microbiological and biogeochemical investigation of the water column of oligotrophic Lake Baikal at the sites of the K2 and Bolshoi mud volcanoes and the Gorevoy Utes oil seep was carried out in July 2013. Total microbial numbers (TMN), cell numbers of type I and type II methanotrophs, and methane concentrations were measured; the rate of methane oxidation was determined. Methane concentrations in Lake Baikal water column varied from 0.09 to 1 μL/L, while methane oxidation rates varied from 0.007 to 0.9 nL/(L day). The highest rates of methane oxidation were revealed in the near-bottom water horizons at the sites of the Bolshoy mud volcano and the Gorevoy Utes oil seep. These were the sites where the most pronounced anomalies in methane concentration were also detected. TMN varied from 0.123 × 10 to 1.64 × 10 cells/mL. Methanotrophic bacteria were revealed in the water column at all sites, their abundance did not always correlate with methane concentrations and the rates of methane oxidation. Methanotrophs constituted not more than 1.63% of the total microbial number, with their highest abundance in the upper 200 m of the water column. [ABSTRACT FROM AUTHOR]

Microbiological, biogeochemical, and isotope geochemical investigations of the upper sediments of the Vistula and Curonian lagoons, Baltic Sea, were carried out. High content of organic matter in the sediments was responsible for the high numbers (over 10 cells cm) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m day and were somewhat higher in the Curonian Lagoon than in the Vistula Lagoon. Integral rates of sulfate reduction were higher in the more saline Vistula Lagoon. Rapid consumption of sulfates of the pore water resulted in intensified methanogenesis, with significantly higher rates detected in the silts of the Curonian Lagoon. High rates of methanogenesis in the Curonian Lagoon correlated with higher methane levels in its upper sediments and near-bottom water. The highest rates of methane oxidation were detected in the uppermost sediment horizons (oxidized or slightly reduced), which was an indication of the barrier role of aerobic methanotrophic bacteria. The calculated methane flows from the sediments into the water column were 0.45 and 0.007 mmol m day for the Vistula and Curonian Lagoons, respectively. Low methane flow from the sediments of the Curonian Lagoon resulted probably from the specific weather (wind) conditions during sampling. The near-stormy conditions in the Curonian Lagoon caused sediment detachment, resulting in methane release into the water column. [ABSTRACT FROM AUTHOR]

Methane content and the rates of microbial processes of the carbon and sulfur cycles were determined for the sediments of the Vyborg Bay, Baltic Sea. Formation of the gas-bearing surface sediments in the Vyborg Bay was found to depend on the activity of the modern microbial processes of the transformation of organic matter, resulting in production of significant amounts of reduced gases (methane and hydrogen sulfide). Rapid consumption of sulfate in the course of sulfate reduction coupled to organic matter decomposition both suppressed anaerobic oxidation of methane and promoted microbial methanogenesis. The gasbearing sediments of this area therefore become a source of methane, and methane concentration in the near-bottom water increases significantly. [ABSTRACT FROM AUTHOR]

The article offers information on the use of the enzyme Methyl-coenzyme M reductase (MCR) in methanotrophy. It states that there are plenty of methane craters in the Baltic Sea which contain large concentrations of methane, gas-saturated sediments and high levels of Anaerobic methane oxidation (AMO). Furthermore, it mentions that within these craters, gene sequence analysis was done on the MCR α subunit (mcrA) to detect the presence of methanotrophic archaea.

The production and oxidation of methane and diversity of culturable aerobic methanotrophic bacteria in the water column and upper sediments of the meromictic oligotrophic Lake Gek-Gel (Azerbaijan) were studied by radioisotope, molecular, and microbiological techniques. The rate of methane oxidation was low in the aerobic mixolimnion, increased in the chemocline, and peaked at the depth where oxygen was detected in the water column. Aerobic methanotrophic bacteria of type II belonging to the genus Methylocystis were identified in enrichment cultures obtained from the chemocline. Methane oxidation in the anaerobic water of the monimolimnion was much more intense than in the aerobic zone. However, below 29–30 m methane concentration increased and reached 68 μM at the bottom. The highest rate of methane oxidation under anaerobic conditions was revealed in the upper layer of bottom sediments. The rate of methane oxidation significantly exceeding that of methane production suggests a deep source of methane in this lake. [ABSTRACT FROM AUTHOR]

Biogeochemical cycle of methane in the Barents Sea was studied using isotope geochemistry to determine the rates of microbial methane oxidation. It was established that microbiological processes (glucose consumption, 14CO2 assimilation, sulfate reduction, and slow methane oxidation) in oxidized surface and weakly reduced sediments are marked by only insignificant change in SO concentration and absence of notable growth of total alkalinity and N/NH4 downward the sediment core. Microbial methane productivity was 0.111 × 106 mol day−1. Taking into account the volume of water column, microbial methane consumption therein can be as much as 1.8 × 106 mol day−1. [ABSTRACT FROM AUTHOR]

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 × 103 cells ml−1 in the northern and eastern parts to 245 × 103 cells ml−1 in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH4l−1 in the eastern part of the sea to 31 nmol CH4l−1 in the northern part of the Herald Canyon. Microbial activity occurred in the upper 0–3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH4dm−3 day−1. The rates of methane oxidation varied from 1.61 to 14.7 nmol CH4dm−3 day−1. The rates of sulfate reduction varied from 1.35 to 16.2 μmol SO dm−1 day−1. The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 μmol SO dm−3 day−1). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 μmol CH4m−2 day−1. [ABSTRACT FROM AUTHOR]

The rate of CO conversion by a pure culture of a thermophilic CO-oxidizing, H2-producing bacterium Carboxydocella sp. strain 1503 was determined by the radioisotopic method. The overall daily uptake of 14CO by the bacterium was estimated at 38–56 μmol CO per 1 ml of the culture. A radioisotopic method was developed to separate and quantitatively determine the products of anaerobic CO conversion by microbial communities in hot springs. The new method was first tested on the microbial community from a sample obtained from a hot spring in Kamchatka. The potential rate of CO conversion by the anaerobic microbial community was found to be 40.75 nmol CO/cm3 sediment per day. 85% of the utilized 14CO was oxidized to carbon dioxide; 14.5% was incorporated into dissolved organic matter, including 0.2% that went into volatile fatty acids; 0.5% was used for cell biomass production; and only just over 0.001% was converted to methane. [ABSTRACT FROM AUTHOR]

Methane emission from the following types of tundra soils was studied: coarse humic gleyey loamy cryo soil, peaty gleyey soil, and peaty gleyey midloamy cryo soil of the arctic tundra. All the soils studied were found to be potential sources of atmospheric methane. The highest values of methane emission were recorded in August at a soil temperature of 8–10°C. Flooded parcels were the sources of atmospheric methane throughout the observation period. The rates of methane production and oxidation in tundra soils of various types were studied by the radioisotope method at 5 and 15°C. Methane oxidation was found to occur in bog water, in the green part of peat moss, and in all the soil horizons studied. Methane production was recorded in the horizons of peat, in clay with plant roots, and in peaty moss dust of the bogey parcels. At both temperatures, the methane oxidation rate exceeded the rate of methane production in all the horizons of the mossy-lichen tundra and of the hillock tundra with flat-bottom depressions. Methanogenesis prevailed only in a sedge-peat moss bog at 15°C. Bacterial enrichment cultures oxidizing methane at 5 and 15°C were obtained. Different types of methanotrophic bacteria were shown to be responsible for methane oxidation under these conditions. A representative of type I methylotrophs oxidized methane at 5°C, and Methylocella tundrae, a psychroactive representative of an acidophilic methanotrophic genus Methylocella, at 15°C. [ABSTRACT FROM AUTHOR]

Microbiological and biogeochemical measurements showed that the intensities of CO2 assimilation, methane oxidation, and sulfate reduction at the Lost City vent field (3° N) reach 3.8 µg C/(1 day), 0.06 µg C/(1 day), and 117 µg S/(1 day), respectively. On the surface of the carbonate structures occurring at this field, two varieties of bacterial mats were found. The first variety, which is specific to the Lost City alkaline vent field, represents jellylike bacterial mats dominated by slime-producing bacteria of several morphotypes. This mat variety also contains chemolithotrophic and heterotrophic microorganisms, either microaerobic or anaerobic. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in this variety reach 747 µg C/(dm3 day), 0.02 µg C/(dm3 day), and 28000 µg S/(dm3 day), respectively. Bacterial mats of the second variety are formed by nonpigmented filamentous sulfur bacteria, which are close morphologically toThiothrix. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in the second mat variety reach 8.2 µg C/(dm3 day), 5.8 µg C/(dm3 day), and 17000 µg S/(dm3 day), respectively. These data suggest the existence of subsurface microflora at the Lost City vent field. [ABSTRACT FROM AUTHOR]

During expeditions in August 1995 and May 1997, the distribution of methane and the rates of its production and oxidation were studied in water and bottom sediments of the north-western shelf of the Black Sea. Experiments that involved the addition of 14CH3COOH and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 560–680 μmol m−2 day−1) were found in coastal sediments in summer-time. In spring, methane production in the same sediments did not exceed 3·6 μmol m−2 day−1. The δ13C values of methane ranged from −70·7 to −81·8‰, demonstrating its microbial origin and contradicting the concept of the migration of methane from the oilfields located on the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of the methane (from 20 to 235 μmol m−2 day−1) arrives at the atmosphere. [Copyright &y& Elsevier]

The aragonite constructions of the Black Sea are formed in a stable anaerobic zone and are a perfect object to study the natural mechanism of anaerobic methane oxidation. The most probable pathway of methane oxidation is its methanogen-mediated reaction with bicarbonates, dissolved in seawater, with the formation of water and acetate, which is then consumed by other components of the anaerobic community. Comparison of the δ13C values of carbonate minerals and organic matter once more demonstrated that the formation of the organic matter of biomass is accompanied by intense fractionation of carbon isotopes, as a result of which the total organic matter of biomass acquires an extremely light isotopic composition, characterized by δ13C values as low as –83.8‰. [ABSTRACT FROM AUTHOR]

In the beginning of the summer of 1999, complex microbiological and biogeochemical investigations of meromictic Lake Mogil'noe (Kil'din Island, Barents Sea) were carried out. The analysis of the results shows a clearly pronounced vertical zonality of the microbial processes occurring in the water column of the lake. To a depth of 8 m, the total number and activity of microorganisms was limited by the relatively low content of organic matter (OM). In the upper part of the hydrogen-sulfide zone of the lake (beginning at a depth of 8.25 m), the content of particulate OM and the microbial number sharply increased. In this zone, the daily production of OM during anaerobic photosynthesis at the expense of massive development of colored sulfur bacteria reached 620 mg C/m2, which was twofold greater than the daily production of phytoplankton photosynthesis and led to a considerable change in the isotopic composition (δ13C) of the particulate OM. In the same intermediate layer, the highest rates of sulfate reduction were recorded, and fractionation of stable sulfur isotopes occurred. Below 10 m was the third hydrochemical zone, characterized by maximum concentrations of H2S and CH4and by a relatively high rate of autotrophic methanogenesis. The comparison of the results obtained with the results of investigations of previous years, performed in the end of summer, shows a decrease in the intensity of all microbial processes inspected. An exception was anoxygenic photosynthesis, which can utilize not only the de novo formed H2S but also the H2S accumulated in the lake during the winter period. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0026261721110011 [ABSTRACT FROM AUTHOR]