Microbiological and biogeochemical investigation of the bottom sediments of semiclosed basins was carried out at the Kislaya Guba tidal power station (Barents Sea) and in Kanda Bay (White Sea). Suppressed tidal water mixing is known to affect the hydrological regime of isolated basins, resulting in the development of oxygen-free sediments. The upper sediments of the studied bays were shown to contain higher concentrations of sulfide and methane, with increased rates of sulfate reduction, methanogenesis, and methane oxidation. The relative abundance of truly marine microorganisms decreased, while microorganisms common in anoxic sediments of meromictic basins developed. The indicator microorganisms with increased relative abundance were archaea of the genera Methanoregula and Methanosaeta. Bacteria of the class Chlorobia, Chloroflexi of the family Anaerolineaceae, and Rhodoferax-related bacteria were indicators of the stagnant seawater. Members of the genus Woeseia were counter-indicators, occurring only in marine water. In our opinion, under reasonably regulated water exchange via the dams, the ecosystems of the Kanda and Kislaya Guba bays may retain the characteristics of marine bays. Otherwise, the studied bays may become stratified basins with anoxic near-bottom water, harboring microbial communities similar to those inhabiting meromictic basins.

Investigations into the microbial community of bottom sediments in the karst Lake Black Kichier were conducted. These sediments exhibited elevated levels of sulfide, dissolved methane, and organic matter. Direct radiotracer experiments revealed substantial rates of microbial processes involved in the decomposition of organic matter. Uncultivated archaea belonging to the phylum Thermoplasmatota were identified within the microbial community. Metagenomic analysis unveiled representatives from five orders: Methanomassiliicoccales, Thermoprofundales (formerly known as Marine Benthic Group D and DHVEG-1), DTX01, SG8-5, and Candidatus Gimiplasmatales (formerly UBA10834). These archaea were previously believed to occur exclusively in deep marine sediments characterized by extreme organic matter scarcity. This discovery reshapes our understanding of the role played by Thermoplasmatota archaea, spanning five orders, in the degradation segment of the carbon cycle.

The data obtained during the recent decades indicate large-scale climatic changes in the Arctic Ocean, especially in the Siberian shelf seas. The impact of shrinking of the Arctic ice cover on marine net primary production (PP) was mostly studied using satellite-derived estimates of chlorophyll-a (Chl a), sea surface temperature, and sea ice concentrations, as well as various modeling approaches. However, no data are available on the quantitative relations between phytoplankton production and heterotrophic bacterioplankton activity in the broadest and shallowest shelf of the World Ocean - the East Siberian Arctic seas (ESAS). In this paper we present a full set of in situ measurements of main PP and microbial heterotrophy characteristics required for better understanding and further validation of the satellite and modeling approaches. In September-October 2011, during the 57th cruise of RV Akademik M.A. Lavrent'ev, PP, bacterioplankton abundance (BA) and bacterioplankton production (BP), as well the rates of dark CO2 assimilation (DCA) were determined in the Chukchi, East Siberian, and Laptev seas and in the Gulf of Anadyr of the Bering Sea (a total of 26 stations) by in situ measurements using radiolabeled bicarbonate. All three important production indicators exhibited significant variance within the studied water areas of the Arctic (PP from 0.98 to 54.7 mu g C L-1 day-1), (BP from 1.1 to 17.1 mu g C L-1 day-1), and (DCA from 0.23 to 8.7 mu g C L-1 day-1). The state of phyto- and bacterioplankton was determined by analysis of the BP/PP and DCA/PP ratios. Active photosynthesis with efficient incorporation of inorganic carbon into the biomass was observed in the Chukchi Sea coastal eastern waters and in the Gulf of Anadyr. On the contrary, the phytoplankton primary production was extremely low in oligotrophic basins of the East Siberian and Laptev seas, while the activity of heterotrophic bacterioplankton consuming organic matter of phytoplankton origin was relatively high. The data of direct measurements can be used for further adjustment of the indirect assessments of production obtained by satellite observations. Glossary East Siberian Arctic seas (ESAS), net primary production (PP), bacterioplankton abundance (BA), bacterial biomass (BB), bacterial production (BP), Arctic Ocean PP (AOPP), organic matter (OM), dissolved organic matter (DOM), colored dissolved organic matter (CDOM), light CO2 assimilation (LCA), dark (heterotrophic + chemotrophic) CO2 assimilation (DCA), production indicators of the surface water layer (PPsurf, DCAsurf, BPsurf), estimated production indicators for the entire depth of the sea (PPint, DCAint, BPint; mg C m- 2 day-1).

The rates of oxygenic and anoxygenic photosynthesis, the microorganisms responsible for these processes, and the hydrochemical characteristics of the sulfide-containing karst lakes, Black Kichier and Big Kichier (Mari El Republic), were investigated. In these lakes, a plate of anoxygenic phototrophic bacteria (APB) is formed at the upper boundary of sulfide occurrence in the water. The phototrophic community of the chemocline zone was analyzed using a combination of high-throughput sequencing of the 16S rRNA gene fragments and light and electron microscopic techniques. Green-colored Chlorobium clathratiforme were absolutely predominant in both lakes. The minor components included green sulfur bacteria (GSB) Chlorobium spp., symbiotic consortia Chlorochromatium magnum and Pelochromatium roseum, purple sulfur bacteria (PSB) Chromatium okenii, and unidentified phylotypes of the family Chromatiaceae, as well as members of the Chloroflexota: Chloronema sp. and Oscillochloris sp. Based on the results of the molecular analysis, the taxonomic status of Ancalochloris perfilievii and other prosthecate GSB, as well as of the PSB Thiopedia rosea, which were visually revealed in the studied freshwater lakes, is discussed.

The relic Lake Mogilnoe, separated from the Barents Sea by a sand and pebble dam, is located in the high Arctic on the Kildin island (Murmansk region). This lake is a classic example of a meromictic basin of marine origin. The data obtained during the 2018 expedition showed changes in the hydrochemical regime of the lake that have occurred over the past 20 years. Sulfide concentration in the monimolimnion of the lake was as high as 140 mg/L. A tendency for salinization of the surface waters to 7 g/L has been noted. The Lake Mogilnoe is characterized by a discrepancy between the halocline and thermocline levels. The chemocline zone in the lake is below the halocline level. In a narrow oxygen-containing layer between 3 and 7.5 m, aerobic microflora of the marine type and marine fauna were present. The bacterial plate was formed at the boundary of the sulfide layer at 8 m and mainly consisted of green sulfur bacteria (GSB). Brown-colored GSB species containing bacteriochlorophyll e were predominant. The previously formed concept of anaerobic phototrophic bacteria (APB) biodiversity based on morphological characteristics was modified using metagenomic data obtained by analyzing DNA from two samples of lake water in the chemocline zone, and was also supplemented by identifying new GSB species. Molecular diagnostic data confirmed the absolute dominance of the brackish species of GSB Chlorobium phaeovibrioides. This is the first isolation and identification of brown- and green-colored Prosthecochloris aestuarii morphotypes from Lake Mogilnoe, as well as of bacteriochlorophyll c-containing Prosthecochloris sp. The taxonomic position of Pelodyction phaem, which was constantly present in the Lake Mogilnoe, is discussed in detail. Despite the partial isolation of the ecosystem of Lake Mogilnoe from the Barents Sea, the main properties of the dominant GSB species and Prosthecochlori aestuarii turned out to be similar to those of the phylotypes living in lakes on the White Sea coast.

The aim of this study was to obtain quantitative hydrological characteristics, intensity of microbial processes and sedimentation conditions in the water column and upper layer of bottom sediments in the Kanda Bay and the basin of the Kislogubskaya tidal power plant. The results of studies in the meromictic reservoirs of the Kanda Bay, artificially separated from the Kandalaksha Gulf by a railway filtering dam at different stages of isolation, and the experience of the operation of the Kislogubskaya TPP and its impact on the basin regime, are an important factor in predicting the origin of hydrogen sulfide contamination during the separation of marine water bodies from the adjacent sea areas, the design of the Northern TPP in the Long Barents Sea Bay and the environmental consequences of the construction of protective dams and dikes, overpasses and embankments when laying roads.

Primary production (PP) and the chlorophyll-a concentration (chl-a) in the European Arctic in the summer of 2020–2021, where continued climatic warming and increased “Atlantification” accelerate the sea ice losses, are discussed. The maximum integrated PP and the total chl-a content were observed in the marginal ice zone (MIZ) of the Barents Sea under weakened stratification of the water column and reached 1109 mgC m–2 day–1 and 118 mg m–2. Near the ice edge in the Nansen Basin, the main part of PP formed in the upper mixed layer and did not exceed 469 mgC m–2 day–1; the chl-a content reached 56 mg m–2. The early and late stages of phytoplankton bloom in the MIZ were characterized by the leading role of picophytoplankton in carbon fixation. Large centric diatoms, microphytoplankton, were recorded to dominate in the MIZ at the stage of peak bloom in 2020 under the dense ice cover of the Nansen Basin. A similar phenomenon was observed earlier only in the Arctic shelf seas and was not recorded in the high-latitude basins of the Arctic Ocean. With the sparse ice cover of the Nansen Basin in 2021, the main primary producers were pico- and nanophytoplankton. The low variability of assimilation numbers (1.7 ± 0.3 mgC mg chl-a–1 h–1) at all bloom stages indicates indirectly the acclimatization of different species of phytoplankton to the environmental changes. The ecological flexibility of the primary production link of the MIZ ecosystems in the studied seas of the European Arctic during the period of climate changes is confirmed.

— Formation of the Kanda Bay resulted from construction of a railway dam (1916) and subsequent isolation of the sea lagoon from the main basin of the Kandalaksha Gulf, White Sea. Decreased action of tidal flows, which mix the water column of the lagoon, altered the hydrological regime of the basin. Decreased water exchange resulted in formation of oxygen-depleted near-bottom water and to sulfide contamination. A freshwater lake was, however, preserved in the southern part of the Kanda Bay. The composition of microbial communities was studied for the near-bottom water horizons at different sides of the Kanda Bay. The oxygen regime in this layer was found to change, with increasing concentrations of sulfide and methane and active processes of sulfate reduction and methane oxidation. The composition of the microbial community changed noticeably, with lower abundance of true marine and freshwater microorganisms and development of bacteria and archaea predominant in microbial communities of anoxic water in meromictic basins. Among the microbial diversity, indicator species with increased abundance were revealed. These are archaea of the genera Methanoregula and Methanosaeta (phylum Halobacterota ). The sulfur cycle microorganisms, which were the indicators of stagnant marine water, included anoxygenic phototrophic bacteria of the class Chlorobia , ( Chlorobium phaeovibrioides, Pelodictyon phaeoclathratiforme ), Chloroflexi of the genus Chloronema , nonsulfur purple bacteria related to the genus Rhodoferax , colorless sulfur bacteria of the family Beggiatoaceae , and sulfur oxidizers of the genus Thiobacillus . Archaea of the genus Nitrosopumilus (phylum Crenarchaeota ) and bacteria of the genus Woeseia may be considered opposites to the indicator microorganisms, since they were found only in the open sea water. In our opinion, stable water exchange through the dam will result in the stable composition of the Kanda Bay microbial community, with only seasonal variations and year-to-year fluctuations. The negative scenario supports prediction of conversion of the Kanda Bay into a stratified basin with anoxic near-bottom water and the microbial community similar to that found in meromictic lakes.

Bottom sediments at methane discharge sites of the Laptev Sea shelf were investigated. The rates of microbial methanogenesis and methane oxidation were measured, and the communities responsible for these processes were analyzed. Methane content in the sediments varied from 0.9 to 37 µmol CH4 dm−3. Methane carbon isotopic composition (δ13C-CH4) varied from −98.9 to −77.6‰, indicating its biogenic origin. The rates of hydrogenotrophic methanogenesis were low (0.4–5.0 nmol dm−3 day−1). Methane oxidation rates varied from 0.4 to 1.2 µmol dm−3 day−1 at the seep stations. Four lineages of anaerobic methanotrophic archaea (ANME) (1, 2a–2b, 2c, and 3) were found in the deeper sediments at the seep stations along with sulfate-reducing Desulfobacteriota. The ANME-2a-2b clade was predominant among ANME. Aerobic ammonium-oxidizing Crenarchaeota (family Nitrosopumilaceae) predominated in the upper sediments along with heterotrophic Actinobacteriota and Bacteroidota, and mehtanotrophs of the classes Alphaproteobacteria (Methyloceanibacter) and Gammaproteobacteria (families Methylophilaceae and Methylomonadaceae). Members of the genera Sulfurovum and Sulfurimonas occurred in the sediments of the seep stations. Mehtanotrophs of the classes Alphaproteobacteria (Methyloceanibacter) and Gammaproteobacteria (families Methylophilaceae and Methylomonadaceae) occurred in the sediments of all stations. The microbial community composition was similar to that of methane seep sediments from geographically remote areas of the global ocean.

The composition and structure of the anoxygenic phototrophic bacterial (APB) community in the water column of meromictic Lake Bol’shie Khruslomeny during winter were investigated. The community developed at the depth of 4.25 m, and its activity in the ice-cover period was very low (6.2 µmol C L–1 day–1). The water in the zone of highest development of phototrophic bacteria was of an unusual lemon-yellow color, probably due to the production and accumulation of polysulfides. The near-bottom water was also of lemon-yellow color and was resistant to oxidation by the air oxygen. In the zone of peak APB development the content of BChl d from green-colored green sulfur bacteria was considerably higher than that of BChl e from brown-colored green sulfur bacteria: 77 and 23

The strain WBS, an anaerobic, psychro- and halotolerant bacterium belonging to the genus Fusibacter, was isolated from the littoral bottom sediments of the White Sea, Arctic, Russia. Fusibacter bizertensis WBS grew at temperatures between 8 and 32 °C (optimum growth at 18-20 °C), pH between 5.2 and 8.3 (optimum growth at pH 7.2), and at NaCl concentrations between 0 and 70 g L-1 (optimum growth at 32 g L-1). It reduced sulfate, thiosulfate, and elemental sulfur into sulfide, and, probably, the strain is able to disproportionate thiosulfate. The strain also utilized a wide range of substrates as it is a chemoorganotrophic bacterium. Analysis of the sequenced genome revealed genes for all enzymes involved in the Embden-Meyerhof glycolytic pathway as well as genes for the non-oxidative stage of the pentose phosphate pathway. The presence of genes encoding aldehyde dehydrogenases and alcohol dehydrogenases also suggests that, in addition to acetate, alcohols can also be the fermentation products. The strain possessed superoxide dismutase and peroxidase activities and the ability to consume O2, which is in full accordance with the presence of corresponding genes of antioxidant defense in the genome. The phylogenetic analysis suggested that the strain WBS is the closest relative of Fusibacter bizertensis LTF Kr01T (16S rRNA gene sequence similarity 98.78%). Based on biochemical and genomic characteristics, the strain WBS is proposed to represent a novel aero-, halo- and psychrotolerant strain from the genus Fusibacter, isolated for the first time among its members from cold oxygenated marine bottom sediments.

The seasonally ice-covered marine region of the European Arctic has experienced warming and sea ice loss in the last two decades. During expeditions in August 2020 and 2021, new data on size-fractioned primary production (PP), chlorophyll a concentration, phytoplankton biomass and composition and carbon fixation rates in the dark were obtained in the marginal ice zone (MIZ) of the Barents Sea, Nansen Basin and Greenland Sea to better understand the response of Arctic ecosystems to ongoing climate changes. Four different situations were observed in the study region: (i) a bloom of the large-cell diatom Podosira glacialis, whose biomass was trapped in a strong halocline at the edge of a dense ice cover; (ii) a bloom of the chain-like colonies of Thalassiosira diatoms on the shelf in mixed waters in fields of shallow ice that could be supported by “fresh” elements in the polynya condition, as well as by terrestrial run-off and drifting ices; at the late stage, this bloom was accompanied by intensive growth of Phaeocystis pouchetti; (iii) dominance of small-cell phytoplankton under weakened stratification and the significant influence of the Atlantic water, depleted of microelements and silicates; (iv) dominance of dinoflagellates of eutrophic water in the contact zone between the water masses of Arctic origin and Atlantic origin in clear water under conditions of increased light intensity. The >10 µm phytoplankton cell size group increased its relative contribution to PP as a response to stratification, light and nutrient load associated with sea ice conditions. Small phytoplankton with sizes < 2 µm formed the basis of total PP in the MIZ regardless of the state of the sea ice.

Despite surprisingly a small number of protein-coding gene in mammalian genomes, a large variety of different RNAs is being produced. These RNAs are amazingly different in their number, size, cell localization, and mechanism of actions. Although new classes of short RNAs (sRNAs) are being continuously discovered, it is not yet obvious how many of the sRNAs are originated. Altogether, the research in the recent few years has identified an unexpectedly rich variety of mechanisms by which noncoding RNAs act, suggesting that we have identified probably only few of the many potential functional mechanism and more investigation will be needed to comprehensively understand the complex nature and biology of mammalian RNAome. Here, we focus on various aspects of the diversity of the biological role of these nonprotein-coding RNAs (ncRNAs), with emphasis, on functional mechanisms recently elucidated.

The composition of microbial communities and the rates of microbial processes in the water column of a meromictic trough in the Biofilter Bay, Kandalaksha Bay, White Sea were investigated in September 2020 and March 2021. The chemocline zone was located at the depths from 8 to 9 m. Sulfide was present in the monimolimnion, its concentration at the bottom reaching 25‒38 mg L–1 (0.7‒1.1 mmol). Conditions of the redox zone favored development of both anaerobic anoxygenic phototrophs and aerobic sulfur-oxidizing chemoautotrophs. A pinkish-brown bacterial plate was formed in this zone. Sequencing of the 16S rRNA gene fragments revealed predominance of green sulfur bacteria (GSB) Chlorobium phaeovibrioides. Aerobic sulfur-oxidizing bacteria Sulfurimonas sp. were the second most abundant group. Plating of chemocline samples on selective media resulted in massive formation of brown-colored Chlorobi colonies, while green GSB colonies were few. Both morphotypes were identified as Chlorobium phaeovibrioides. At the time of our study, purple sulfur bacteria (PSB) did not form a bacterial plate in the redox zone, although few PSB colonies were revealed. The PSB isolate was identified as Thiocapsa rosea. Members of this species are able to switch from photosynthesis to aerobic chemosynthesis and may compete for sulfide with sulfur-oxidizing chemo-autotrophs. We suggest that due to its openness the Biofilter Bay meromictic trough may act as a source for the propagation of anoxygenic phototrophic bacteria in the Kandalaksha Bay.

The results of studying the emission, content, and isotopic composition of methane in soils of the active layer in the zones of typical and southern shrubby tundra of the western Russian Arctic are presented. Methane in the soils of the active layer is of biogenic origin. The maximum methane contents have been recorded in the bogs and the catchment depressions amounting to 1.11 ± 0.95 mg CH4/kg with a maximum value of 4.6 mg CH4/kg. In the well-drained landscapes, the methane content is significantly lower. For the bog landscapes, a strong correlation between methane contents in the soils and sums of positive air temperatures has been determined. Climate warming causes an increase in the methane content in the soils of the active layer and higher methane emission. The gradient distribution of the methane content and its isotopic composition in water-saturated and drained soils indicates a significant contribution of the diffusion mechanism to the methane transport to the surface.

Research regarding the conditions and processes of paleo- and modern sedimentation with an assessment of particles and pollution fluxes, with determination of the rates of biogeochemical processes and regional paleoclimatic reconstructions in the contact area of cold Polar and warm Atlantic water masses under the influence of cold (seep) and hot (hydrothermal) fluids were carried out during the expedition in the Norwegian-Greenland Sea Area and the Barents Sea. The consequences of atlantification are recorded in all components of the geosystems of the Barents Sea and the high-latitude Arctic as well as the reverse effect of the Arctic amplification on the geosystems of the northern North Atlantic occurring both at the present time and in the Pleistocene and Holocene.

Biogeochemical processes involving microorganisms play an important role in marine sedimentogenesis. The study of biogeochemical processes in the Barents Sea was carried out from 1997 with interruptions until 2019. Using a complex of geological-geochemical, microbiological, radioisotope and stable isotope methods, it was possible to obtain a quantitative estimate of the total abundance and biomass of microorganisms, rates of biogeochemical processes, methane content and organic matter suspended. In the course of work in four expeditions, it was found that in the surface (0–10 m) water column south of 74° N the magnitude of the total abundance and the biomass of microorganisms increased by 2019 by about 5 times compared to 1998. To the north, in colder waters, the total abundance and the biomass of organisms were lower than in the southern region of the sea. The methane concentration in the surface layer of the water column at the border with the atmosphere did not change much for 20 years (1976–1997) and increased noticeably from 1997 to 2017, from 3.3 to 15.8 nM. The increase in FFM, the biomass of organisms and the concentration of methane in the water column is associated with the melting of glaciers, with the release of organic matter of continental origin released from ice into the water. The results of the work indicate changes in the ecosystem of the Barents Sea.

Уникальный природный объект — реликтовое озеро Могильное на о.Кильдин в Баренцевом море — известен давно. В научной и популярной литературе есть немало публикаций о многослойности его водной толщи, а также о его необычных обитателях. Статья посвящена истории микробиологических исследований и микробиологам, уже более века работающим на оз.Могильном, а также тем удивительным микроорганизмам, ради которых ученые стремятся на суровый остров Кильдин.

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.