S. K. Yusupov

Microbial Processes of the Carbon and Sulfur Cycles in Lake Shira (Khakasia)

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.

Microbial processes at the aerobic-anaerobic interface in the deep-water zone of the black sea

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).

Distribution, diversity, and activity of sulfate-reducing bacteria in the water column in Gek-Gel Lake, Azerbaijan

The distribution and activity of sulfate-reducing bacteria (SRB) in the water column of the alpine meromictic Gek-Gel lake were studied. Apart from traditional microbiological methods based on cultivation and on measuring the process rates with radioactive labels, in situ fluorescent hybridization (FISH) was used, which enables identification and quantification without cultivating organisms. The peak rate of sulfate reduction, 0.486 µg S 1−1 day−1, was found in the chemocline at 33 m. The peak SRB number of 2.5×106 cells/ml, as determined by the most probable number method on selective media, was found at the same depth. The phylogenetic affiliation of the SRB, as determined by FISH, revealed the predominance of the Desulfovibrio spp., Desulfobulbus spp., and Desulfoarculus spp./Desulfomonile spp. groups. The numbers of spore-forming Desulfotomaculum spp. increased with depth. The low measured rates of sulfate reduction accompanied by high SRB numbers and the predominance of the groups capable of reducing a wide range of substrates permit us to assume utilization of electron acceptors other than sulfate as the main activity of the SRB in the water column.

[Desulfacinum subterraneum sp.nov.--a new thermophilic sulfate-reducing bacterium isolated from a high temperature oil field ].

A new thermophilic sulfate-reducing bacterium isolated from the high-temperature White Tiger oil field (Vietnam) is described. Cells of the bacterium are oval (0.4–0.6 by 0.6–1.8 μm), nonmotile, non-spore-forming, and gram-negative. Growth occurs at 45 to 65°C (with an optimum at 60°C) at NaCl concentrations of 0 to 50 g/l. In the course of sulfate reduction, the organism can utilize lactate, pyruvate, malate, fumarate, ethanol, salts of fatty acids (formate, acetate, propionate, butyrate, caproate, palmitate), yeast extract, alanine, serine, cysteine, and H2+ CO2(autotrophically). In addition to sulfate, the bacterium can use sulfite, thiosulfate, and elemental sulfur as electron acceptors. In the absence of electron acceptors, the bacterium can ferment pyruvate and yeast extract (a yet unrecognized capacity of sulfate reducers) with the formation of acetate and H2. The G+C content of DNA is 60.8 mol %. The level of DNA–DNA hybridization of the isolate (strain 101T) and Desulfacinum infernum(strain BαG1T) is as low as 34%. Analysis of the nucleotide sequence of 16S rDNA places strain 101Tin the phylogenetic cluster of the Desulfacinumspecies within the sulfate reducer subdivision of the delta subclass of Proteobacteria. All these results allowed the bacterium studied to be described as a new species, Desulfacinum subterraneumsp. nov., with strain 101 as the type strain.

Microbiological and isotopic-geochemical investigations of meromictic lakes in Khakasia in winter

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.

The Biogeochemical Cycle of Methane in the Coastal Zone and Littoral of the Kandalaksha Bay of the White Sea

Microbiological and biogeochemical investigations of the processes of methane production (MP) and methane oxidation (MO) in the coastal waters and littoral of the Kandalaksha Bay of the White Sea were carried out. The studies were conducted in the coastal zones and in the water areas of the Kandalaksha Preserve, Moscow State University White Sea Biological Station, and the Zoological Institute (RAS) biological station in August 1999, 2000, and 2001 and in March 2001. The rate of CO2 assimilation in the shallow and littoral sediments was 35–27 800 μg C/(dm3 day) in summer and 32.8–88.9 μg C/(dm3 day) in winter. The maximal rates of MP were observed in the littoral sediments in the zone of macrophyte decomposition, in local depressions, and in the estuary of a freshwater creek (up to 113 μl/(dm3 day)). The maximal level of MO was observed in the shallow estuarine sediments (up to 2450 μl/(dm3 day)). During the winter season, at the temperature of –0.5 to 0.5°C, the MP rate in the littoral sediments was 0.02–0.3 μl/(dm3 day), while the MO rate was 0.06–0.7 μl/(dm3 day). The isotopic data obtained indicate that the Corg of the mats and of the upper sediment layers is enriched with the heavy 13C isotope by 1–4‰ as compared to the Corg of the suspension. A striking difference was found between the levels of methane emission by the typical littoral microlandscapes. In fine sediments, the average emission was 675 μl CH4/(m2 day); in stormy discharge stretch sediments, it was 1670 μl CH4/(m2 day); and under stones and in silted pits, 1370 μl CH4/(m2day). The calculation, performed with consideration of the microlandscape areas with a high production, allowed the CH4 production of 1 km2 of the littoral to be estimated as 192–300 l CH4/(km2 day).

The effect of microorganisms and seasonal factors on the isotopic composition of particulate organic carbon from the black sea

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.

Methane formation and oxidation in the meromictic oligotrophic Lake Gek-Gel (Azerbaijan).

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

The biogeochemical cycle of methane on the northwestern shelf of the Black Sea

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.

Energy sources for diagenesis: Evidence from the Black 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.