E F Veslopolova

Microbiological and isotopic geochemical investigation of Lake Kislo-Sladkoe, a meromictic water body at the Kandalaksha Bay shore (White Sea)

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.

Sulfate reduction, methanogenesis, and methane oxidation in the Holocene sediments of the Vyborg Bay, Baltic Sea

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.

Microbiological and biogeochemical properties of the Caspian Sea sediments and water column

The work presents the results of investigation of microbial and biogeochemical processes at the water-sediment interface in the samples of three Caspian Sea profiles obtained during the 39th cruise of RV “Rift” in May–June 2012. The decrease in suspended Corg content from the surface to the bottom resulted from the activity of aerobic heterotrophic microorganisms. Autotrophic methanogenesis occurred in anoxic water of deep-sea depressions, where methane concentrations were up to 2.2–3.75 μL CH4 L−1, which was an order of magnitude higher than in the aerobic water column (0.04–0.32 μL CH4 L−1). Methanogenesis was accompanied by a considerable decrease in δ13C of suspended Corg (−26 to −30‰). The numbers of microbial cells in the water column varied from 40 to 3200 × 103 cells mL−1. The results of microbiological and biogeochemical investigation demonstrated that, in spite of the absence of connection with the ocean and other specific features, the Caspian Sea has the characteristics of a typical marine basin.

Succession Processes in the Anoxygenic Phototrophic Bacterial Community in Lake Kislo-Sladkoe (Kandalaksha Bay, White Sea)

The community of anoxygenic phototrophic bacteria (APB) in the water column of Lake Kislo- Sladkoe (Kandalaksha Bay, White Sea), which has recently become separated from the sea, was investigated in March?April 2012, March?April 2013, and in September 2013. The lake, which was previously considered meromictic, was in fact mixed and was strongly affected by the sea. In winter the lake is sometimes washed off with seawater, and this together with the seasonal cycles of succession processes determines the succession of the community. The consequences of the mixing in autumn 2011 could be observed in the APB community as late as autumn 2013. Green-colored green sulfur bacteria (GSB) usually predominated in the chemocline. In winter 2013 stagnation resulted in turbidity of water under the ice, which was responsible for both predominance of the brown GSB forms and the changes ratio of the species of purple sulfur bacteria (PSB) in anoxic water layers. Production of anoxygenic photosynthesis in the lake was at least 240 mg C m-2 day-1 in September and 0–20 mg C m–2 day–1 in March—April, which corresponded to 40 and 69%, respectively, of oxygenic photosynthesis. Okenone-containing purple sulfur bacteria, strain TcakPS12, were isolated in 2012 from lake water. The ells of this strain form filaments of not separated cells. Strain TcakPS12 exhibited 98% similarity with the type strains of Thiocapsa pendens DSM 236 and Thiocapsa bogorovii BBS, as well as with the strains AmPS10 and TcyrPS10, which were isolated from Lake Kislo-Sladkoe in 2010.

The sulfate-reducing bacterial community of sulfide-rich water of the Ust’-Kachka resort spring, Perm Krai, Russia

Microbiological investigation of the highly mineralized, sulfide-rich cold spring of the Ust’-Kachka resort was carried out. The total number and biomass of microbial cells were 50 × 103 cell/mL and 15 μg/L, respectively. While the total microbial number was low, the sulfate reduction rate determined by the radioisotope method was relatively high (0.575 mg S L−1 day−1). An enrichment culture was obtained on Widdel medium. According to the results of cloning the 16S rRNA gene fragments with subsequent restriction analysis, the dominant organisms were group 6 sulfate-reducing bacteria (Desulfovibrio-Desulfomicrobium) and the microorganism exhibiting 99% similarity to the anaerobic haloalkaliphilic bacterium Halanaerobium hydrogeniformans.

[Abundance and activity of microorganisms at the water-sediment interface and their effect on the carbon isotopic composition of suspended organic matter and sediments of the Kara Sea].

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.

Sharp water column stratification with an extremely dense microbial population in a small meromictic lake, Trekhtzvetnoe: Sharp water column stratification

Located on the shore of Kandalaksha Bay (the White Sea, Russia) and previously separated from it, Trekhtzvetnoe Lake (average depth 3.5 m) is one of the shallowest meromictic lakes known. Despite its shallowness, it features completely developed water column stratification with high-density microbial chemocline community (bacterial plate) and high rates of major biogeochemical processes. A sharp halocline stabilizes the stratification. Chlorobium phaeovibrioides dominated the bacterial plate, which reached a density of 2 × 108 cell ml-1 and almost completely intercepts H2 S diffusion from the anoxic monimolimnion. The resulting anoxygenic photosynthesis rate reached 240 μmol C l-1 day-1 , exceeding the oxygenic photosynthesis rate in the mixolimnion. The rates of other processes are also high, reaching 4.5 μmol CH4 l-1 day-1 for methane oxidation and 35 μmol S l-1 day-1 for sulfate reduction. Metagenomic analysis demonstrated that the Chl. phaeovibrioides population in the bacterial plate layer had nearly clonal homogeneity, although some fraction of these cells harbour a plasmid. The Chlorobium population was associated with bacteriophages that share homology with CRISPR spacers in the host. These features make the ecosystem of the Trekhtzvetnoe Lake a valuable model for studying regulation and evolution processes in natural high-density microbial systems.

Study of the microbial processes in the water column and bottom sediments of the Dolgaya-Vostochnaya Bay (Barents Sea) before construction of the northern tidal power plant

798 1 Tidal power plants (TPP) are alternative sources of energy production. Long-term observations of the TPP at the Kislaya Bay on the Barents Sea and the Rance TPP on the Atlantic coast of France [1, 2] indicate that the construction and operation of the Northern TPP (Dolgaya-Vostochnaya Bay) may change the current state of this water basin. Possible adverse effects may include contamination of the near-bottom horizon with sulfide due to the activity of sulfate-reducing bacteria. Activation of sulfate reduction has been described for a number of marine environments in various degrees of isolation from the offshore waters [3–8]. The disturbance of the operating regime at the Kislogubskaya TPP from 1974 to 1982, which resulted in a decrease in the water exchange with the sea to 2–3% [1], is a perfect example of rapid environmental change. Limitation of water exchange resulted in severe demineralization of the 15-m surface horizon, decreased mixing of the water column, and accumulation of sulfide at depths below 20 m, resulting in mass death of benthic animals.