Search

Methane oxidation rates and diversity of methane-oxidizing microorganisms were studied in the upper sediment layers of the Laptev Sea (methane seep area, Lena fore-delta, shelf, and upper slope not affected by seeps and river flow). The highest methane concentrations and methane oxidation rates (up to 1.16 µmol СН4 dm−3 day−1) were revealed at the seep stations. Carbon dioxide was the main product of methane oxidation at all stations. Sequencing of the 16S rRNA gene fragments revealed microorganisms of the class Gammaproteobacteria, order Methylococcales. Since the share of methanotrophs was high at the sites of constant gas seepage (up to 1.93% of the total read number), they could be detected by sequencing of the native samples. Phylogenetic diversity of methane-oxidizing bacteria was not high, and all detected microorganisms belonged to the Deep-Sea 1 cluster. On the phylogenetic tree, the sequences formed a cluster together with the genus Methyloprofundus. Members of the genera Methylomonas and Methylobacter related to methanotrophs inhabiting freshwater ecosystems were revealed in enrichments from the coastal stations sediment samples.

There is still a lack of understanding of H2S formation in agricultural waste, which leads to poor odour prevention and control. Microbial sulfate reduction is a major process contributing to sulfide formation in natural and technogenic environments with high sulfate and low oxygen concentration. Agricultural waste can be considered a low-sulfate system with no obvious input of oxidised sulfur compounds. The purpose of this study was to characterise a microbial community participating in H2S production and estimate the microbial sulfate reduction rate (SRR) in manure slurry from a large-scale swine finishing facility in Western Siberia. In a series of manure slurry microcosms, we identified bacterial consortia by 16S rRNA gene profiling and metagenomic analysis and revealed that sulfate-reducing Desulfovibrio were key players responsible for H2S production. The SRR measured with radioactive sulfate in manure slurry was high and comprised 7.25 nmol S cm−3 day−1. Gypsum may be used as a solid-phase electron acceptor for sulfate reduction. Another plausible source of sulfate is a swine diet, which often contains supplements in the form of sulfates, including lysine sulfate. Low-sulfur diet, manure treatment with iron salts, and avoiding gypsum bedding are possible ways to mitigate H2S emissions from swine manure.

Abstract— 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.

Comparative study of methanogen diversity and potential activity of different methanogenic pathways in the sediments of young thermokarst and mature polygenetic Yamal lakes was carried out. The hydrogenotrophic pathway of methanogenesis played an important role in methane formation in thermokarst lakes. The acetoclastic and methylotrophic pathways were also revealed there. In a polygenetic lake with a dissolved organic matter content closest to that of the thermokarst lakes, methanogenesis proceeded more intensively, and the relative abundance of methanogens, especially acetoclastic ones, was higher than in thermokarst lakes. The activity of methyl-reducing methanogens was also assumed there. Methanogens of the genera Methanothrix and Methanoregula, as well as representatives of the family Methanomassiliicoccaceae were identified in the sediments of all lakes. Methane-oxidizing bacteria (Methylobacter, Candidatus “Methylomirabilis”) and archaea (Ca. “Methanoperedens”) were also detected.

Although dissimilatory sulfate reduction (DSR) is an important microbial process in subterranean aquifers, its geochemical consequences in this ecosystem remain insufficiently studied. The absence of data on the process rate under in situ conditions prevents quantitative estimation of the sulfur reservoir. This research is aimed at investigation of microbial sulfate reduction in subterranean aquifers associated with the Severnaya coal mine in Kuzbass. Water samples were collected from an artesian borehole broaching the underground horizons of the flooded mine. During over 10 years of sampling the water temperature fluctuated within a narrow range (10–13°C); the water was anoxic (–112 to –174 mV) and contained up to 6 mg/L sulfide. Analysis by high-throughput sequencing of the 16S rRNA genes showed that sulfur-oxidizing bacteria Sulfurovum, Sulfuricurvum, Sulfurospirillum, and Thiothrix predominated in the community. No phylotypes with known ability to carry out DSR were detected. Measurement of sulfate reduction rates with $${\text{Na}}_{{\text{2}}}^{{{\text{35}}}}{\text{S}}{{{\text{O}}}_{{\text{4}}}},$$ showed the process to be relatively active, resulting in up to 178 g of reduced sulfur per year at the borehole discharge. Two organisms representing minor components of the community, a psychrophilic and acidophilic Desulfomicrobium sp. DI and a moderately thermophilic Desulfotomaculum LL1, were isolated in pure culture by varying the cultivation condition in a bioreactor. These members of the “rare biosphere” may be responsible for production of reduced sulfur species, which are used by a diverse and numerous sulfur-oxidizing community.

The results of field studies of the species composition and productive parameters (biomass, photosynthesis rate, chlorophyll a content, and assimilation numbers) of microalgae in the plankton and the interstitial icy waters of Lake Baikal southern littoral area obtained in March 2018 are presented. A comprehensive study of the ice and phytoplankton algae showed that their productive activity was relatively low at most stations. Their higher values observed near river mouths with significant anthropogenic pollution were caused by both the additional nutrient input and development of small-sized algae, primarily of phytoflagellates, which indicate water pollution by organic matter inflowing to Lake Baikal with its tributaries. Using the principal component method, we failed to reveal reliable correlation between the primary producers and the microorganisms decomposing organic matter into mineral substances (the correlation coefficient was 0.49). The differences between the stations subject to anthropogenic impact and the reference ones indicate that access to easily mineralized organic matter promoted the massive development of phytoflagellates. Although large-cell diatoms common in the lake were absent, primary production at these sites reached 100 to 280 mg C m−2, which was comparable with the values obtained for abundant diatom blooms during the under-ice period. High functional potential of the algae at the areas subject to anthropogenic impact results in significant biomass accumulation, which leads eutrophication of the littoral zone and may lead to increased primary production of the pelagic zone.

A combination of physicochemical and radiotracer analysis, high-throughput sequencing of the 16S rRNA, and particulate methane monooxygenase subunit A (pmoA) genes was used to link a microbial community profile with methane, sulfur, and nitrogen cycling processes. The objects of study were surface sediments sampled at five stations in the northern part of the Barents Sea. The methane content in the upper layers (0–5 cm) ranged from 0.2 to 2.4 µM and increased with depth (16–19 cm) to 9.5 µM. The rate of methane oxidation in the oxic upper layers varied from 2 to 23 nmol CH4 L−1 day−1 and decreased to 0.3 nmol L−1 day−1 in the anoxic zone at a depth of 16–19 cm. Sulfate reduction rates were much higher, from 0.3 to 2.8 µmol L −1 day −1. In the surface sediments, ammonia-oxidizing Nitrosopumilaceae were abundant, the subsequent oxidation of nitrite to nitrate can be carried out by Nitrospira sp. Aerobic methane oxidation could be performed by uncultured deep-sea cluster 3 of gamma-proteobacterial methanotrophs. Undetectable low levels of methanogenesis were consistent with a near complete absence of methanogens. Anaerobic methane oxidation in the deeper sediments was likely performed by ANME-2a-2b and ANME-2c archaea in consortium with sulfate-reducing Desulfobacterota. Sulfide can be oxidized by nitrate-reducing Sulfurovum sp. Thus, the sulfur cycle was linked with the anaerobic oxidation of methane and the nitrogen cycle, which included the oxidation of ammonium to nitrate in the oxic zone and denitrification coupled to the oxidation of sulfide in the deeper sediments. Methane concentrations and rates of microbial biogeochemical processes in sediments in the northern part of the Barents Sea were noticeably higher than in oligotrophic areas of the Arctic Ocean, indicating that an increase in methane concentration significantly activates microbial processes.

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.

Microbiological, molecular ecological, biogeochemical, and isotope geochemical research was carried out at the polar Lake Bol'shie Khruslomeny at the coast of the Kandalaksha Bay, White Sea in March and September 2017. The uppermost mixolimnion was oxic, with low salinity (3-5%). The lower chemocline layer was brown-green colored, with very high content of particulate organic matter (up to 11.8 mg C L-1). The lowermost monimolimnion had marine salinity (22-24%) and very high concentrations of sulfide (up to 18 mmol L-1) and CH4 (up to 1.8 mmol L-1). In the chemocline, total microbial abundance and the rate of anoxygenic photosynthesis were 8.8 × 106 cells mL-1 and 34.4 μmol C L-1 day-1, respectively. Both in March and September, sulfate reduction rate increased with depth, peaking (up to 0.6-1.1 μmol S L-1 day-1) in the lower chemocline. Methane oxidation rates in the chemocline were up to 85 and 180 nmol CH4 L-1 day-1 in March and September, respectively; stimulation of this process by light was observed in September. The percentages of cyanobacteria and methanotrophs in the layer where light-induced methane oxidation occurred were similar, ∼2.5% of the microbial community. Light did not stimulate methane oxidation in deeper layers. The carbon isotope composition of particulate organic matter (δ13C-Corg), dissolved carbonates (δ13C-DIC), and methane (δ13C- CH4) indicated high microbial activity in the chemocline. Analysis of the 16S rRNA gene sequences revealed predominance of Cyanobium cyanobacteria (order Synechococcales) in the mixolimnion. Green sulfur bacteria Chlorobium phaeovibrioides capable of anoxygenic photosynthesis constituted ∼20% of the chemocline community both in March and in September. Methyloprofundus gammaptoteobacteria (family Methylomonaceae) were present in the upper chemocline, where active methane oxidation occurred. During winter, cyanobacteria were less abundant in the chemocline, while methanotrophs occurred in higher horizons, including the under-ice layer. Chemolithotrophic gammaproteobacteria of the genus Thiomicrorhabdus, oxidizing reduced sulfur compounds at low oxygen concentrations, were revealed in the chemocline in March. Both in March and September archaea constituted up to 50% of all microorganisms in the hypolimnion. The percentage of putative methanogens in the archaeal community was low, and they occurred mainly in near-bottom horizons.

We analysed the relationship between the chemical complex (concentration of dissolved ions, nutrients, pH) and biological parameters (primary production, biomass of phytoplankton, abundance and activity of bacterial communities) at estuaries of rivers and coastal waters of Southern Baikal during the under-ice period. Correlation network analysis revealed CO2 to be the main limiting factor for the development of algae and microbial communities in the coastal zone of Lake Baikal. This study indicates that primarily reverse synthesis of bicarbonate and carbonate ions associated with the development of phytoplankton and accumulation of dissolved CO2 during photosynthesis regulates pH in the Baikal water. We did not detect the anthropogenic factors that influence the change in pH and acidification. Near the Listvyanka settlement (Lake Baikal, Listvennichnaya Bay), there was a great number of organotrophs and thermotolerant bacteria with low bacterioplankton activity and high concentration of organic carbon. This evidences eutrophication due to the influx of organic matter having an anthropogenic source. Nutrients produced during the bacterial destruction of this matter may explain the changes in bottom phytocenoses of Listvennichnaya Bay.

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).

The rates of microbial processes and phylogenetic diversity of the microorganisms responsible for organic matter production and decomposition in the benthic communities and bottom sediments of the rivers Solyanka, Lantsug, Khara, Chernavka, and Bol’shaya Smorogda (Lake Elton area, Volgograd oblast, Russia) were studied. The biomass and primary production of cyano–bacterial communities varied significantly within the ranges of 20–903 mg Chl a/m2 and 0.2–21 mg C/(m2 h), respectively. Depending on the season, the share of anoxygenic CO2 fixation varied from 20% to the values comparable to the rate of oxygenic photosynthesis. The total heterotrophic activity of microbial communities determined as the rate of dark CO2 assimilation varied from 31 to 750 μmol/(dm3 day) in the mats and from 3 to 137 μmol/(dm3 day) in the sediments. The rates of sulfate reduction and hydrogenotrophic methanogenesis varied from 10 to 2621 μmol S/dm3 day) and from 1.5 to 323 nmol CH4/(dm3 day), respectively. High-throughput sequencing of the 16S rRNA genes in cyano–bacterial mats revealed microorganisms belonging to 20 phyla, with the sequences of Cyanobacteria, Proteobacteria, and Bacteroidetes being the most numerous.

Integrated studies on the hydrochemistry and water column rates of microbial processes in the eastern sector of the Black Sea along a standard 100-miles transect off Gelendzhik from the coast to the central part of the sea at water depths of 100–2170 m show that a series of warm winters and the absence of intense convective winter mixing resulted in a relatively low content of suspended particulate matter (SPM), particulate organic carbon (POC), and nutrients in the water column in March 2009. The relatively high SPM concentrations and the presence of isotopically light POC at the offshore station are indicative of the supply of terrigenous material from land and low contributions of phytoplanktonic organic matter to the composition of SPM. This may explain the low rates of biogeochemical processes in the water column near the coast. The surface layer at deep-water stations is dominated by isotopically heavy phytoplanktonic organic matter. This suggests that the supply of terrigenous material from land was insufficient in offshore deep-water areas. Therefore, warm winters and insufficient nutrient supply do not prevent photosynthesis in the photic layer of the deep-water zone, which generates organic substrates for heterotrophic aquatic communities. The results of isotopic analysis of POC, measurements of the rates biogeochemical processes, and the hydrochemical characteristics of the water column can be used to determine the nature and seasonal variability of the POC composition.

Seasonal variations in marine primary production (PP) in the coastal zone of the south-eastern part of the Baltic Sea were studied between April 2008 and April 2009. The spring PP maximum was observed to be limited by the concentration of nitrates. Following a decrease in photosynthetic consumption of nutrients, an increase in ammoniacal nitrogen due to the decomposition of organic matter and concomitant increase in the biomass of diazotrophic cyanobacterial species, the growth of phytoplankton was limited by phosphates. By the middle of summer, concentrations of nitrate and phosphates had reached the analytical minimum (0.07 mmol m − 3 and 0.06 mmol m−3, respectively). Terrestrial runoff, whose maximum occurred during the spring–summer decline of phytoplankton growth, had a moderately positive influence on PP, with the annual rate reaching the eutrophic level (290 g C m − 2 yr − 1); however, the seasonal cycle was typical for mesotrophic waters of temperate latitudes of the Northern Hemisphere. The most significant producers of phytoplankton biomass (PB) were representatives of the Dinophyta, Chlorophyta and Cyanophyta systematic divisions at the study site. 77% of carbon-to-chlorophyll a ratio variability was determined by the seasonal variations in green algae biomass. During the spring bloom, dinoflagellates provided the highest contribution in the total biomass in comparison with diatoms.

Microbiological, biogeochemical, and isotopic geochemical investigation of Lake Kislo-Sladkoe (Polusolenoe in early publications) at the Kandalaksha Bay shore (White Sea) was carried out in September 2010. Lake Kislo-Sladkoe was formed in the mid-1900s out of a sea gulf due to a coastal heave. At the time of investigation, the surface layer was saturated with oxygen, while near-bottom water contained sulfide (up to 32 mg/L). Total number of microorganisms was high (12.3 × 106 cells/mL on average). Light CO2 fixation exhibited two pronounced peaks. In the oxic zone, the highest rates of photosynthesis were detected at 1.0 and 2.0 m. The second, more pronounced peak of light CO2 fixation was associated with activity of anoxygenic phototrophic bacteria in the anoxic layer at the depth of 2.9 m (413 μg C L−1 day−1). Green-colored green sulfur bacteria (GSB) predominated in the upper anoxic layer (2.7–2.9 m), their numbers being as high as 1.12 × 104 cells/mL, while brown-colored GSB predominated in the lower horizons. The rates of both sulfate reduction and methanogenesis peaked in the 2.9 m horizon (1690 μg S L−1 day−1 and 2.9 μL CH4 L−1 day-1). The isotopic composition of dissolved methane from the near-bottom water layer (δ13C (CH4) = −87.76‰) was significantly lighter than in the upper horizons (δ13C (CH4) = −77.95‰). The most isotopically heavy methane (δ13C (CH4) = −72.61‰) was retrieved from the depth of 2.9 m. The rate of methane oxidation peaked in the same horizon. As a result of these reactions, organic matter (OM) carbon of the 2.9 m horizon became lighter (−36.36‰), while carbonate carbon became heavier (−7.56‰). Thus, our results demonstrated that Lake Kislo-Sladkoe is a stratified meromictic lake with active microbial cycles of carbon and sulfur. Suspended matter in the water column was mostly of autochthonous origin. Anoxygenic photo-synthesis coupled to utilization of reduced sulfur compounds contributed significantly to OM production.

ISSN 1028334X, Doklady Earth Sciences, 2013, Vol. 453, Part 1, pp. 1094–1099. © Pleiades Publishing, Ltd., 2013.Original Russian Text © M.V. Ivanov, A.S. Savvichev, A.A. Klyuvitkin, A.L. Chul’tsova, E.E. Zakharova, I.I. Rusanov, A.Yu. Lein, A.P. Lisitsyn, 2013, published in DokladyAkademii Nauk, 2013, Vol. 453, No. 1, pp. 76–81.

At ten stations of the meridian profile in the eastern Kara Sea from the Yenisei estuary through the shallow shelf and further through the St. Anna trough, total microbial numbers (TMN) determined by direct counting, total activity of the microbial community determined by dark CO2 assimilation (DCA), and the carbon isotopic composition of organic matter in suspension and upper sediment horizons (δ13C, ‰) were investigated. Three horizons were studied in detail: (1) the near-bottom water layer (20–30 cm above the sediment); (2) the uppermost, strongly hydrated sediment horizon, further termed fluffy layer (5–10 mm); and (3) the upper sediment horizon (1–5 cm). Due to a decrease in the amount of isotopically light carbon of terrigenous origin with increasing distance from the Yenisei estuary, the TMN and DCA values decreased, and the δ13C changed gradually from −29.7 to −23.9‰. At most stations, a noticeable decrease in TMN and DCA values with depth was observed in the water column, while the carbon isotopic composition of suspended organic matter did not change significantly. Considerable changes of all parameters were detected in the interface zone: TMN and DCA increased in the sediments compared to their values in near-bottom water, while the 13C content increased significantly, with δ13C of organic matter in the sediments being at some stations 3.5–4.0‰ higher than in the near-bottom water. Due to insufficient illumination in the near-bottom zone, newly formed isotopically heavy organic matter (δ13C ∼ −20‰) could not be formed by photosynthesis; active growth of chemoautotrophic microorganisms in this zone is suggested, which may use reduced sulfur, nitrogen, and carbon compounds diffusing from anaerobic sediments. High DCA values for the interface zone samples confirm this hypothesis. Moreover, neutrophilic sulfur-oxidizing bacteria were retrieved from the samples of this zone.

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 1010 cells cm−3) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO2 assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m−2 day−1 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−2 day−1 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.

Isotopic compositions of organic (δ13C-Corg) and carbonate (δ13C-Ccarb) carbon were analyzed in the particulate matter (hereafter, particulates) and sediments from the North and Middle Caspian basins. Isotopic composition of Corg was used for assessing proportions of the allochthonous and autochthonous organic matter in the particulates. Difference between the δ13C-Corg values in surface sediments and particulates is explained by the aerobic and anaerobic diagenetic transformations. Isotopic composition of Corg in sediments may be used as a tool for reconstructing the Quaternary transgressive-regressive history of the Caspian Sea.

Complex investigations of recent and Drevnechernomorian (ancient Black Sea) sediments from the outer shelf, continental slope, and deep-water basin of the Russian Black Sea sector have been carried out using samples collected during cruise of the R/V Professor Shtokman organized by the Institute of Oceanology of the Russian Academy of Sciences (March 2009) and expedition of “YUZHMORGEO” (summer 2006). Rates of the main anaerobic processes during diagenesis (sulfate reduction, dark CO2 fixation, methanogenesis, and methane oxidation) were studied for the first time in sediment cores of the studied area. Two peaks in the rate of microbial processes and two sources of these processes were identified: the upper peak near the water-sediment contact is related to the solar energy (OM substrate of the water column) and the lower peak at the base of the Drevnechernomorian sediments with high(>1000 μM) methane concentration related to the energy of anaerobic methane oxidation. The neogenic labile OM formed during this process is utilized by other groups of microorganisms. According to experimental data, the daily rate of anaerobic methane oxidation is many times higher than that of methanogenesis, which unambiguously indicates the migration nature of the main part of methane.

Fluorescent in situ hybridization (FISH) was used to analyze the abundance and phylogenetic composition of sulfate-reducing bacteria in the aerobic waters and in the oxic/anoxic transitional zone (chemocline) of the Black Sea, where biogenic formation of reduced sulfur compounds was detected by radioisotope techniques. Numerous sulfate-reducing bacteria of the genera Desulfotomaculum (30.5% of detected bacterial cells), Desulfovibrio (29.6%), and Desulfobacter (6.7%) were revealed in the aerobic zone at a depth of 30 m, while Desulfomicrobium-related bacteria (33.5%) were prevalent in the upper chemocline waters at 150-m depth. Active cells of sulfate-reducing bacteria were much more abundant in the samples collected in summer than in the winter samples from the deep-sea zone. The presence of physiologically active sulfate reducers in oxic and chemocline waters of the Black Sea correlates with the hydrochemical data on the presence of reduced sulfur compounds in the aerobic water column.

The results of microbiological, biogeochemical, and isotope geochemical studies in the Kara Sea are described. The samples for these studies were obtained during the 54th voyage of the research vessel Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Gulf of Ob. The quantitative characteristics of the total bacterial population and the activity of the microbial processes in the water column and bottom sediments were obtained. The total population of the bacterioplankton (BP) varied from 250000 cells/ml in the northern water area to 3000000 cells/ml in the Gulf of Ob. The BP population depended on the content of the water suspension. The net BP production was minimal in the central water area, amounting to 0.15–0.2 μg C/(l day), and maximal (0.5–0.75 μg C/(l day)) in the Gulf of Ob. The organic material at the majority of the stations in the Ob transect predominantly contained light carbon isotopes (−28.0 to −30.18‰) of terrigenous origin. The methane content in the surface water layer varied from 0.18 to 2.0 μl CH4/l, and the methane oxidation rate changed in the range of 0.1–100 nl CH4/(l day). The methane concentration in the upper sediment layer varied from 30 to 300 μl CH4/dm3; the rate of the methanogenesis was 44 to 500 nl CH4/(dm3 day) and that of the methane oxidation, 30 to 2000 nl CH4/(dm3 day). The rate of the sulfate reduction varied from 4 to 184 μg S/(dm3 day).

The rates of photosynthesis and dark CO2 fixation were determined in 12 soda lakes of the Kulunda steppe. Characterization of the phototrophic communities was given, and the cell numbers of anoxygenic phototrophic bacteria (APB) were determined. The photosynthetic production in different lakes was substantially different, constituting from 0.01 to 1.32 g C m−2 day−1. The main part of carbon dioxide was assimilated in the process of oxygenic photosynthesis. Anoxygenic photosynthesis was recorded only in 5 of the 12 lakes studied. Its values varied between 0.06 and 0.42 g C m−2 day−1, constituting from 8 to 34% of the total photosynthetic activity. Anoxygenic photosynthesis was revealed in the lakes where the number of APB reached 107–109 CFU cm−3. Dark CO2 fixation constituted 0.01–0.15 g C m−2 day−1. Positive correlation was observed between the primary production value and water alkalinity. No relationship between productivity and water mineralization was revealed in the 30–200 g l−1 range, whereas an increase in salinity above 200 g l−1 suppressed the photosynthetic activity. The mechanisms of influence of the environmental factors on the rate of photosynthesis are discussed.

Mass-spectrometric investigation of carbon isotope composition (delta13C) was carried out for suspended organic matter and dissolved mineral compounds for the water column of some meromictic water bodies differing in salinity and trophic state. As a rule, a more pronounced carbon isotope fractionation (resulting from the metabolism of phytoplankton and anoxygenic phototrophic bacteria) was revealed in the zones of enhanced oxygenic and anoxygenic photosynthesis. Carbon isotope fractionation at the border between oxidized and reduced waters depends both on the activity of microbial communities and on the dominant species of phototrophic microorganisms. Analysis of the distribution profiles of the isotopic composition of suspended organic matter and dissolved mineral carbon revealed active mineralization of the organic matter newly formed via anoxygenic photosynthesis in the monimolimnion by microbial communities, resulting in the release of isotopically light carbon dioxide. Mineral carbon in the anaerobic zones of highly productive meromictic water bodies is therefore enriched with the light 12C isotope.

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 x 10(3) cells ml(-1) in the northern and eastern parts to 245 x 10(3) cells ml(-1) in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH4 l(-1) in the eastern part of the sea to 31 nmol CH4 l(-1) in the northern part of the Herald Canyon. Active microbial processes occurred in the upper 0-3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH4 dm(-3) day(-1). The rates of methane oxidation varied from 1.61 to 14.7 nmol CH4 dm(-3) day(-1). The rates of sulfate reduction varied from 1.35 to 16.2 micromol SO4(2-) dm(-3) day(-1). The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 micromol SO4(2-) 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 micromol CH4 m(-2) day(-1).

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 SO42− 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.

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.

Study of biogeochemical processes in water and sediments of the Chukchi Sea in August 2004 revealed atypical maximums of the concentration of biogenic elements (N, P, and Si) and the rate of microbial sulfate reduction in the surface layer (0–3 cm) of marine sediments. The C: N: P ratio in the organic matter (OM) of this layer does not fit the Redfield-Richards stoichiometric model. Specific features of biogeochemical processes in sea are likely related to the complex dynamics of water, high primary productivity (110–1400 mg C/(m2 day)), low depth of basin (

The biogeochemical and molecular biological study of the chemocline and sediments of saline meromictic lakes Shira and Shunet (Khakasia, 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 the members of domains 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 correlated with the measured rates of sulfate reduction and methanogenesis.

Hydrothermal solutions were examined in a circulation system that started to develop after the 1991 volcanic eruption in the axial EPR segment between 9°45′ N and 9°52′ N. Within the twelve years elapsed after the eruption, the diffusion outflow of hot fluid from fractures in basaltic lavas gave way to focused seeps of hot solutions through channels of hydrothermal sulfide edifices. The example of field Q demonstrates that the concentrations of H2S decreased from 86 to 1 mM/kg from 1991 to 2003, and the Fe/H2S ratio simultaneously increased by a factor of 1.7, a fact that can explain the disappearance of the microbial mats, which were widespread at the fields before 1991. The S isotopic composition of H2S is independent of the H2S concentration, a fact testifying to the rapid evolution of the hydrothermal system in the early years of its evolution. Carbon in CH4 from the hot fluid sampled in 2003 is richer in the light 12C isotope than carbon in the fluid from the hydrothermal field at 21° N in EPR, which suggests that methane comes to field Q from more than one source. The composition of particulate matter in the hydrothermal solutions indicates that it was contributed by biological material. Experimental solutions with labeled substrates (t < 70°C) show evidence of the active processes of methane oxidation and sulfate reduction. Our results indicate that, during the 12 years of the evolution of the hydrothermal system, the composition of its solutions evolved and approached the compositions of solutions in mature hydrothermal systems in EPR.

An anaerobic phototrophic bacterial community in Lake Mogilnoe, a relict lake on Kil'din Island in the Barents Sea, was studied in June 1999 and September 2001. Irrespective of the season, the upper layer of the anaerobic zone of this lake had a specific species composition of sulfur phototrophic bacteria, which were dominated by the brown-colored green sulfur bacterium Chlorobium phaeovibrioides. The maximum number of sulfur phototrophic bacteria was observed in June 1999 at a depth of 9 m, which corresponded to a concentration of bacteriochlorophyll (Bchl) e equal to 4.6 mg/l. In September 2001, the maximum concentration of this pigment (3.4 mg/l) was found at a depth of 10 m. In both seasons, the concentration of Bchl a did not exceed 3 μg/l. Purple sulfur bacteria were low in number, which can be explained by their poor adaptation to the hydrochemical and optical conditions of the Lake Mogilnoe water. In June 1999, the water contained a considerable number of Pelodictyon phaeum microcolonies and Prosthecochloris phaeoasteroides cell chains, which was not the case in September 2001. A 16S rDNA-based phylogenetic analysis of pure cultures of phototrophic bacteria isolated from the lake water confirmed that the bacterial community is dominated by Chl. phaeovibrioides and showed the presence of three minor species, Thiocystis gelatinosa, Thiocapsa sp., and Thiorhodococcus sp., the last of which is specific to Lake Mogilnoe.

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (δ13C) and hydrogen sulfide and sulfate (δ34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.

In May 1998, during the fifty-first voyage on board the research vessel Professor Vodyanitskii, a comparative study was conducted of the species diversity of green and purple sulfur bacteria in the water column of the chemocline zone at deep-sea stations and on the bottom surface of the Black Sea shallow regions. At three deep-sea stations, the accumulation of photosynthetic bacteria in the chemocline zone at a depth of 85–115 m was revealed on the basis of the distribution of potential values of carbon dioxide light fixation. The location of the site of potential carbon dioxide light fixation suggests that the photosynthesis may be determined by the activity of the brown Chlorobium sp., earlier revealed at these depths. Enrichment cultures of brown sulfur bacteria were obtained from samples taken at the deep-sea stations. By morphology, these bacteria, assigned to Chlorobium sp., appear as nonmotile straight or slightly curved rods 0.3–0.5 × 0.7–1.2 µm in size; sometimes, they form short chains. Ultrathin sections show photosynthetic antenna-like structures, chlorosomes, typical of Chlorobiaceae. The cultures depended on the presence of NaCl (20 g/l) for growth, which corresponds to the mineralization of Black Sea water. The bacteria could grow photoautotrophically, utilizing sulfide, but the Black Sea strains grew much more slowly than the known species of brown sulfur bacteria isolated from saline or freshwater meromictic lakes. The best growth of the strains studied in this work occurred in media containing ethanol (0.5 g) or sodium acetate (1 g/l) and low amounts of sulfide (0.4 mM), which is consistent with the conditions of syntrophic growth with sulfidogens. The data obtained allow us to conclude that the cultures of brown sulfur bacteria are especially adapted to developing at large depths under conditions of electron donor deficiency owing to syntrophic development with sulfate reducers. The species composition of the photosynthetic bacteria developing in the bottom sediments of shallow stations differed substantially from that observed at deep-sea stations. Pure cultures of the green Chlorobium sp. BS 1C and BS 2C (chlorobactin as the carotenoid), purple sulfur bacteria Chromatium sp. BS 1Ch (containing spirilloxanthine series pigments), and Thiocapsa marina BS 2Tc (containing the carotenoid okenone) were obtained from samples of sediments at shallow-water stations. Brown sulfur bacteria were absent in the sediment samples obtained from the Black Sea shallow-water stations 1 and 2.

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 studies of the meromictic saline Lake Shira (Khakasia) were conducted. In the upper part of the hydrogen-sulfide zone, at a depth of 13.5–14 m, there was a pale pink layer of water due to the development of purple bacteria (6 × 105 cells/ml), which were assigned by their morphological and spectral characteristics toLamprocystis purpurea (formerly Amoebobacter purpureus). In August, the production of organic matter (OM) in Lake Shira was estimated to be 943 mg C/(m2day). The contribution of anoxygenic photosynthesis was insignificant (about 7% of the total OM production). The share of bacterial chemosynthesis was still less (no more than 2%). In the anaerobic zone, the community of sulfate-reducing bacteria played a decisive role in the terminal decomposition of OM. The maximal rates of sulfate reduction were observed in the near-bottom water (114 μg S/(l day)) and in the surface layer of bottom sediments (901 μg S/(dm3 day)). The daily expenditure of Corg for sulfate reduction was 73% of Corg formed daily in the processes of oxygenic and anoxygenic photosynthesis and bacterial chemosynthesis. The profile of methane distribution in the water column and bottom sediments was typical of meromictic reservoirs. The methane content in the water column increased beginning with the thermocline (7–8 m) and reached maximum values in the near-bottom water (17 μl/l). In bottom sediments, the greatest methane concentrations (57 μl/l) were observed in the surface layer (0–3 cm). The integral rate of methane formation in the water column and bottom sediments was almost an order of magnitude higher than the rate of its oxidation by aerobic and anaerobic methanotrophic microorganisms.

Microbiological and biogeochemical investigations of the coastal zone and the littoral of the Kandalaksha Bay of the White Sea were carried out. The material for investigations was obtained in the series of expeditions of the Institute of Microbiology, Russian Academy of Sciences, in August 1999, 2000, 2001, and in March 2003. The studies were conducted on the littoral and in the water area of the Kandalaksha Preserve, the Moscow University Belomorsk Biological Station, and the Zoological Institute Biological Station, Russian Academy of Sciences. Sediment sampling on the littoral was carried out in the typical microlandscapes differing in the sediment properties and macrobenthos distribution. The maximal sulfate reduction rate (SRR) was shown for the shallow part of the Chernorechenskaya Bay (up to 2550 μg S/(dm3 day)) and in the Bab'ye More Bay (up to 3191 μg S/(dm3 day)). During the winter season, at a temperature of –0.5 × 0.5°C, the SRR in the sediments of the Kartesh Bay was 7.9 × 13 μg S/(dm3 day). In the widest limits, the SRR values varied in the sediment cores sampled on the littoral. The minimal values (11 μg S/(dm3 day)) were obtained in the core samples on the silt–sandy littoral. The littoral finely dispersed sediments rich in organic matter were characterized by high SRR values (524–1413 μg S/(dm3 day)). The maximal SRR values were shown for the sediments present within the stretch of decomposing macrophytes, in local pits at the lower littoral waterline, and in the mouth of a freshwater stream (51–159 mg S/(dm3 day)). A sharp difference in the level of H2S production in the type microlandscapes was shown. The average hydrogen sulfide production in finely dispersed sediments constituted 125 mg S/(m2 day); in stormy discharge deposits, 1950 mg S/(m2 day); in depressions under stones and in silted pits, 4300 mg S/(m2 day). A calculation made with regard to the area of microlandscapes with increased productivity shows that the daily H2S production per 1 km2 of the littoral (August) is 60.8 to 202 kg S/(km2 day), while the organic carbon consumption for sulfate reduction per 1 km2 of the littoral is 46 to 152 kg Corg/(km2 day).

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.

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 μmol/(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 μmol/(m2 day). 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 cold seeps or from the oil fields 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 6.8 to 320 μmol/(m2 day)) arrives in the atmosphere.

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.

Within the mass of recent (unit-I) and ancient Black Sea (unit-II) sediments on the outer shelf of the Russian sector of the Black Sea, the rates of anoxic processes participating in diagenetic transformations of carbon and sulfur compounds were first measured using 35S and 14C radioactive tracers. The main energy source for biogeochemical processes in (unit-I) sediments is the organic matter (OM) supplied to the bottom from the water mass. In (unit-II) sediments, this is methane in a migratory form proved by the excess of its oxidation rate over that of its generation. In recent silt, the primary microbial process is sulfate reduction; in unit-II, this is methane anoxic oxidation by the consortium of archeides and sulfate reductants. The organic matter produced in methane oxidation, in turn, acts as an energy source for the community of anaerobic heterotrophic microorganisms in the bottom sediments, which are remote from the water-sediment interface.

Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane, and sulfate reduction) occurring at the aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at intervals of 5–10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m2 day) with a maximum at the boundary of cyclonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rates of methane oxidation and methane production suggests that methane that is oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m2 day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m2 day)), in the eastern halistatic region. The average rate of hydrogen sulfide production measured at three deep-sea stations amounted to 755 mg S/(m2 day), or 276 g S/(m2 year).

The isotopic composition of particulate organic carbon (POC) from the Black Sea deep-water zone was studied during a Russian-Swiss expedition in May 1998. POC from the upper part of the hydrogen sulfide zone (the C-layer) was found to be considerably enriched with the12C isotope, as compared to the POC of the oxycline and anaerobic zone. In the C-layer waters, the concurrent presence of dissolved oxygen and hydrogen sulfide and an increased rate of dark CO2 fixation were recorded, suggesting that the change in the POC isotopic composition occurs at the expense of newly formed isotopically light organic matter of the biomass of autotrophic bacteria involved in the sulfur cycle. In the anaerobic waters below the C-layer, the organic matter of the biomass of autotrophs is consumed by the community of heterotrophic microorganisms; this results in weighting of the POC isotopic composition. Analysis of the data obtained and data available in the literature allows an inference to be made about the considerable seasonable variability of the POC δ13C value, which depends on the ratio of terrigenic and planktonogenic components in the particulate organic matter.

Box and gravity cores recovered from the Hakon Mosby mud volcano (HMMV) during cruise 15 of the R/V Professor Logachev were analyzed for bacterial activity and benthic fauna distribution. The high bacterium number (up to 9.6×109 cells cm-3 of the sediment) and marked rates of sulfate reduction (up to 0.155 mg S dm-3 day-1) and methane oxidation (up to 9.9 μg C dm-3 day-1) were shown for the upper horizons of the sediments of the HMMV peripheral zone. The benthic community is characterized by the presence of two pogonophoran species, Oligobrachia sp. and Sclerolinum sp., harboring symbiotic methanotrophic bacteria.

Processes of inorganic carbon assimilation, methanogenesis, sulfate reduction, and acetate oxidation to CO 2 occurring in samples from the East Pacific Rise at 13°N were traced, using radioisotopically labeled substrates, at temperatures ranging from 65 to 100°C. Molecular hydrogen stimulated lithotrophic methanogenesis and sulfate reduction but inhibited inorganic carbon assimilation. Active mineralization of acetate was observed in an organic-rich Alvinella -associated system at 80°C. Members of the Thermococcales were the most numerous hyperthermophilic archaea in these samples, their density achieving 10 8 cells per cm 3 , while the numbers of cultured hydrogen-utilizing thermophilic lithotrophs were several orders of magnitude lower.

Carbon monoxide (CO) is one of the common gaseous compounds found in hot volcanic environments. It is known to serve as the growth substrate for a number of thermophilic prokaryotes, both aerobic and anaerobic. The goal of this work was to study the process of anaerobic transformation of CO by microbial communities inhabiting natural thermal environments: hot springs of Uzon Caldera, Kamchatka. The anaerobic microbial community of Treshchinny Spring (80°C, pH 6.5) was found to exhibit two peaks of affinity for CO (K S1 = 54 nM and K S2 = 1 μM). The actual rate of anaerobic CO transformation by the microbial community of this spring, calculated after obtaining the concentration dependence curve and extrapolated to the natural concentration of CO dissolved in the hot spring water (20 nM), was found to be 120 μmol l−1 of sediment day−1. In all the hot springs studied, more than 90% of the carbon of 14CO upon anaerobic incubation was recovered as 14CO2. From 1 to 5% of 14CO was transformed to volatile fatty acids (VFA). The number of microorganisms capable of anaerobic CO oxidation determined by dilution-to-extinction method reached 106 cells ml−1 of sediment. CO-transforming anaerobic thermophilic microorganisms isolated from the springs under study exhibited hydrogenogenic type of CO oxidation and belonged to the bacterial genera Carboxydocella and Dictyoglomus. These data suggest a significant role of hydrogenogenic carboxydotrophic prokaryotes in anaerobic CO transformation in Uzon Caldera hot springs.

Sulfidogenic activity (SA) in anoxic sediments of several soda lakes with variable salinity in south Kulunda Steppe (Altai, Russia) has been investigated. The study included in situ measurements of sulfate reduction rates and laboratory experiments with sediment slurries in which sulfate, thiosulfate or elemental sulfur were used as electron acceptors. Despite the extreme conditions (high salt concentrations and high pH), the SA values were relatively high (ranging from 0.02 to 1.20 μmol HS− cm−3 h−1), and only hampered under salt-saturated conditions. The highest SA was observed with elemental sulfur, followed by thiosulfate, while the lowest SA was determined in the presence of sulfate. Of all the electron donors tested, the addition of formate resulted in the highest SA with all three sulfur electron acceptors. Surprisingly, hydrogen as an electron donor had very little effect. Acetate was utilized as an electron donor only under sulfur-reducing conditions. Indigenous populations of sulfidogens in soda lake sediments showed an obligately alkaliphilic pH response of SA, showing a pattern that corresponded well to the in situ pH conditions. Sulfate reduction was much more susceptible to salt inhibition than thiosulfate and sulfur reduction. Microbiological investigations indicated that sulfate-reducing bacteria belonging to the orders Desulfovibrionales and Desulfobacterales could very likely be responsible for the SA with sulfate and thiosulfate as electron acceptors at moderate salt concentrations. Sulfur reduction at moderate salinity was carried out by a specialized group of haloalkaliphilic sulfur-reducing bacteria that utilize volatile fatty acids. In saturated soda brine, extremely natronophilic representatives of the order Halanaerobiales were responsible for the sulfur-dependent respiration.

Fluorescent in situ hybridization (FISH) was used to analyze the abundance and phylogenetic composition of physiologically active anaerobic microbial communities [sulfate-reducing bacteria (SRB) and methanogenic archaea] in the aerobic waters and in the oxic/anoxic transitional zone (chemocline) of the Black Sea. Biogenic sulfate reduction and methane formation were detected at these horizons by radioisotope techniques. Numerous SRB phylogenetically related to Desulfotomaculum (30.5% of detected bacterial cells), Desulfovibrio (29.6%), and Desulfobacter (6.7%) were detected in the aerobic zone at a depth of 30 m, whereas Desulfomicrobium-related bacteria (33.5%) were prevalent in chemocline at a depth of 150 m. In the oxic subsurface water layer, Methanomicrobiales-related archaea and subgroup 1 methanogens constituted up to 62 and 35.3% of archaeal cell, respectively. The active cells of sulfate-reducing and methanogenic microorganisms were much more abundant in the samples collected in summer than in winter from the deep-sea zone. The presence of physiologically active anaerobic microorganisms in oxic and chemocline waters of the Black Sea correlates with the hydrochemical data on the presence of sulfide and methane at corresponding depths.