Hydrochemical and biogeochemical processes in Lake Khilganta were studied during more than ten years. The lake was shown to pass through periods of wetting and drying. This is accompanied by considerable changes in water chemistry and microbiological processes. During the passage from a wet to a dry period, lake water mineralization increases from 40 to 260 g/l and pH decreases from 9.9 to 7.1. At the same time, the isotope composition of organic matter carbon in bottom deposits becomes lighter (from −15.6 to −30.6‰), as well as that of carbon in carbonates (from +4.1 to −8.6‰), due to the lower rate of photosynthetic processes in lake bacterial mats. The order of salt precipitation during the passage from a wet to a dry period and the mechanism of maintaining water pH are considered. A possible similarity between the modern processes in Lake Khilganta and the processes in analogous Pre-Cambrian water bodies is discussed, and the hypothesis regarding the possibility of wider development of soda water bodies at early stages of Earth’s history is considered.

The flux rates of carbon dioxide, methane, and nitrous oxide in the soils on autonomous, transitional, transitional-accumulative, and accumulative positions of a catena on the Oka River’s right bank (Moscow oblast) were assessed using the chamber method. The lowest rate of C-CO 2 emission (18.8–29.8 mg/m 2 per hour) was found for the gray forest soil in the autonomous position, and the highest rate (52.4–66.1 mg/m 2 per hour) was found for the alluvial meadow soil of the accumulative landscape. In the summer, the uptake of methane from the atmosphere exceeded its release from the soil at all the points of the catena (9–38 μg/m 2 per hour). The highest rate of the C-CH 4 uptake was observed for the soil in the transitional position. In the fall, the soils in the autonomous, transitional, and transitional-accumulative positions served as a sink of C-CH 4 , and the soil of the accumulative position was a source of methane emission. The rate of the N-N 2 O emission from the catena soils increased when going from the autonomous position to the accumulative one (0.41–11.2 μg/m 2 per hour). The spatial variation of the C-CO 2 , C-CH 4 , and N-N 2 O fluxes within the catena was 33, 172, and 138%, respectively. The upper (0- to 10-cm) soil layer made the major contribution to the emission of carbon dioxide. This soil layer was characterized by its C-CH 4 uptake, and the emission of methane was typical for the deeper (0- to 20-cm) layer. The layers deeper than 10 and 20 cm emitted more N-N 2 O than the surface layer.

A mesophilic alkalitolerant aboriginal bacterial community capable of autotrophic thiocyanate decomposition under aerobic and oxygen-free conditions was isolated from reused water of a metallurgical works. The growth of the aboriginal bacterial community was optimal at pH 9.0. Ammonium and sulfate were the end products of thiocyanate decomposition under both aerobic and oxygen-free conditions. Under oxygen-free conditions, thiocyanate decomposition occurred in the presence of nitrate. Nitrite was accumulated as an intermediate product in the course of denitrification, and was subsequently used as an electron acceptor for thiocyanate oxidation. Dinitrogen was the end product of denitrification.

Soda lakes are characterized by an intense sulfur cycle that begins with sulfidogenesis. Model laboratory experiments that involved combining of pure cultures showed that, during anaerobic decomposition of cellulose by Clostridium alkalicellulosi , the sulfate-reducing bacteria (SRB) of the species Desulfonatronovibrio hydrogenovorans, Desulfonatronum lacustre , and Desulfonatronum cooperativum , different in their nutritional requirements, may directly use the cellulose fermentation products for sulfidogenesis without mediatory microorganisms. In binary cocultures with SRB, the amount of the H 2 S formed constituted from one-third to two-thirds of the cellulose [H] equivalents; acetate was among the products formed. When the syntrophic Contubernalis alkalaceticum , capable of acetate oxidation, was incorporated into the trophic chain along with hydrogenotrophic SRB, the amount of the H 2 S formed exceeded by 33–42% the amount of the [H] equivalents in the utilized cellulose, water being the source of additional hydrogen. Thus, the trophic pathway from plant residues to sulfide, previously considered to be the longest in the alkaliphilic microbial community, may involve a minimal number of stages and do without intermediate participation of dissipotrophic fermenting organisms.

Для содовых озер характерен интенсивный серный цикл, который начинается сульфидогенезом. В лабораторных модельных экспериментах путем комбинирования чистых культур алкалофильных микроорганизмов показано, что при анаэробном разложении целлюлозы Clostridium alkalicellulosi возможно прямое, без посредников, использование продуктов брожения целлюлозы на сульфидогенез сульфатредуцирующими бактериями (СРБ) видов Desulfonatronovibrio hydrogenovorans, Desul-fonatronum lacustre, Desulfonatronum cooperativum, различающихся пищевыми потребностями. В бинарных комбинациях с СРБ количество образованного H2S составило 1/3–2/3 эквивалентов [H] целлюлозы, а в составе продуктов оставался ацетат. При включении в трофическую цепь синтрофного Contubernalis alkalaceticum, способного к окислению ацетата в паре с гидрогенотрофными СРБ, количество образованного H2S на 33–42% превышало эквиваленты [H] использованной целлюлозы. Источником дополнительного водорода могла служить вода. Таким образом, наиболее длинный для алкалофильного микробного сообщества трофический маршрут от растительных остатков до сульфида может осуществляться в минимальное число этапов без промежуточного участия бродильщиков-диссипотрофов.

The physicochemical and microbial characteristics of some medium-temperature hydrotherms of Kamchatka Peninsula (Uzon caldera), habitats of the hoverfly Eristalinus sepulchralis larvae, were studied. In these hydrothermal vents, the larvae were found to use various prokaryotic and eukaryotic microorganisms as a nutrient substrate. The rates of chemo-and photosynthetic activity of the suspended microbial communities inhabiting the hydrotherms and supporting the existence of larvae were measured. By light and electron microscopy, exo-and endosymbiotic prokaryotic microorganisms were revealed in the digestive and respiratory systems of larvae.

It has been shown that the intracellular concentrations of Na + , K + , and Cl − ions in Desulfonatronum thiodismutans depend on the extracellular concentration of Na + ions. An increase in the extracellular concentration of Na + results in the accumulation of K + ions in cells, which points to the possibility that these ions perform an osmoprotective function. When the concentration of the NaCl added to the medium was increased to 4%, the concentration gradient of Cl − ions changed insignificantly. It was found that D. thiodismutans contains two forms of hydrogenase—periplasmic and cytoplasmic. Both enzymes are capable of functioning in solutions with high ionic force; however they exhibit different sensitivities to Na + , K + , and Li + salts and pH. The enzymes were found to be resistant to high concentrations of Na + and K + chlorides and Na + bicarbonate. The cytoplasmic hydrogenase differed significantly from the periplasmic one in having much higher salt tolerance and lower pH optimum. The activity of these enzymes depended on the nature of both the cationic and anionic components of the salts. For instance, the inhibitory effect of NaCl was less pronounced than that of LiCl, whereas Na + and Li + sulfates inhibited the activity of both hydrogenase types to an equal degree. The highest activity of these enzymes was observed at low Na + concentrations, close to those typical of cells growing at optimal salt concentrations.

The decline of methane oxidizing activities in gray forest soil upon its conversion into arable land was shown to be caused by major changes in biotic and physicochemical properties of soil. Using the method of immune serums, methane-oxidizing bacteria were detected in both forest and agricultural soils, but their populations differed significantly in both abundance and composition. In the forest soil, the number of methanotrophs was an order of magnitude higher than in arable soil, amounting to 3.5 × 108 and 0.24 × 108 cells/g soil, respectively. All methane-oxidizing bacteria identified in the forest soil belonged to the genus Methylocystis, and 94% of these were represented by a single species, M. parvus. The arable soil was dominated by type I methanotrophs (Methylobacter and Methylomonas, 67.6%), occurring along with bacteria of the genus Methylocystis. In addition, arable soil is characterized by a low content of microbial biomass, lower porosity and water resistance of soil aggregates, and the predominance of nitrogen mineralization processes over those of nitrogen immobilization. These factors can also contribute to lower rates of methane oxidation in arable soil as compared to forest soil.

The adaptation of microorganisms to life in brines allows two strategies: the accumulation of organic osmoregulators in the cell (as in many moderate halophiles, halomonads in particular) or the accumulation of inorganic ions at extremely high intracellular concentrations (as, for example, in haloanaerobes). To reveal the regularities of osmoregulation in haloalkaliphiles developing in soda lakes, Halomonas campisalis Z-7398-2 and Halomonas sp. AIR-2 were chosen as representatives of halomonads, and Natroniella acetigena, as a representative of haloanaerobes. It was established that, in alkaliphilic halomonads, the intracellular concentrations of inorganic ions are insufficient for counterbalancing the environmental osmotic pressure and balance is attained due to the accumulation of organic osmoregulators, such as ectoine and betaine. On the contrary, the alkaliphilic haloanaerobe N. acetigena employs K+, Na+, and Cl− ions for osmoregulation. High intracellular salt concentrations increasing with the content of Na+ in the medium were revealed in this organism. At a concentration of 1.91 M Na+ in the medium, N. acetigena accumulated 0.83 M K+, 0.91 M Na+, and 0.29 M Cl− in cells, and, with an increase in the Na+ content in the medium to 2.59 M, it accumulated 0.94 M K+, 1.98 M Na+, and 0.89 M Cl−, which counterbalanced the external osmotic pressure and provided for cell turgor. Thus, it was shown that alkaliphilic microorganisms use osmoregulation strategies similar to those of halophiles and these mechanisms are independent of the mechanism of pH homeostasis.

Microbiological and biogeochemical measurements showed that the intensities of CO2 assimilation, methane oxidation, and sulfate reduction in the Lost City vent field (30 degrees N) reach 3.8 microg C/(1 day), 0.06 microg C/(1 day), and 117 microg S/(1 day), respectively. On the surface of the carbonate structures occurring in this field, two varieties of bacterial mats were found. The first variety, which is specific to the Lost City alkaline vent field, represents jelly bacterial mats dominated by slime-producing bacteria of several morphotypes. This mat variety also contains chemolithotrophic and heterotrophic microorganisms, either microaerobic or anaerobic. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in this variety reach 747 microg C/(dm3 day), 0.02 microg C/(dm3 day), and 28,000 microg S/(dm3 day), respectively. Bacterial mats of the second variety are formed by nonpigmented filamentous sulfur bacteria, which are close morphologically to Thiothrix. The intensities of CO2 assimilation, methane oxidation, and sulfate reduction in the second mat variety reach 8.2 microg C/(dm3 day), 5.8 microg C/(dm3 day), and 17,000 microg S/(dm3 day), respectively. These data suggest the existence of subsurface microflora in the Lost City vent field.

Seasonal fluctuations in the methane fluxes in the soil–atmosphere system were determined for gray forest soils of Central Russia. Consumption of atmospheric methane was found to exceed methane emission in gray forest soils under forest and in the agrocenosis. The average annual rates of atmospheric methane consumption by the soil under forest and in the agrocenosis were 0.026 and 0.008 mg C-CH 4 /(m 2 h), respectively. The annual rate of atmospheric methane oxidation in the gray forest soils of Moscow oblast was estimated to be 0.68 kton. Seasonal fluctuations in the methane oxidation activity were due to changes in the hydrothermal conditions and in the reserves of readily decomposable organic matter and mineral nitrogen, as well as to changes in the activity of methane oxidizers.

The activity of methanogenic and methanotrophic bacteria was evaluated in bottom sediments of Lake Baikal. Methane concentration in Baikal bottom sediments varied from 0.0053 to 81.7 ml/dm3. Bacterial methane was produced at rates of 0.0004-534.7 microliters CH4/(dm3 day) and oxidized at rates of 0.005-1180 microliters CH4/(dm3 day). Peak methane production and oxidation were observed in Frolikha Bay near a methane vent. Methane was emitted into water at rates of 49.2-4340 microliters CH4/(m2 day). Rates of bacterial methane oxidation in near-bottom water layers ranged from 0.002 to 1.78 microliters/(1 day). Methanogens and methanotrophs were found to play an important role in the carbon cycle through all layers of sediments, particularly in the areas of methane vent and gas-hydrate occurrence.

The activity of methanogenic and methanotrophic bacteria was evaluated in bottom sediments of Lake Baikal. Methane concentration in Baikal bottom sediments varied from 0.0053 to 81.7 ml/dm 3. Bacterial methane was produced at rates of 0.0004-534.7 μl CH 4/(dm 3 day) and oxidized at rates of 0.005-1180 μl CH 4/(dm 3 day). Peak methane production and oxidation were observed in Frolikha Bay near a methane vent. Methane was emitted into water at rates of 49.2-4340 μl CH 4/(m 2 day). Rates of bacterial methane oxidation in near-bottom water layers ranged from 0.002 to 1.78 μl/(l day). Methanogens and methanotrophs were found to play an important role in the carbon cycle through all layers of sediments, particularly in the areas of methane vent and gas-hydrate occurrence.

A colorless sulfur bacterium of the genus Thioploca , which forms bacterial mats, was studied in the region of underwater thermal vents (Frolikha Bay, northern Baikal). The organism occurs under microaerobic conditions in top sediment layers, and its biomass can amount to 65 mg of wet weight per 1 kg of silt. Individual filaments of the bacterium penetrate the anaerobic zone to the depth of 19 cm. Thioploca is distributed in a mosaic pattern over the bottom of the bay. Thioploca mats are typically found near vents that discharge low-temperature underground water. In the form of separate filaments, this bacterium is more widely distributed in the top sediment layer, particularly in sediments with a more active sulfate reduction. The bacteria from the deep-water and coastal areas of the bay have different morphology. Cells of Thioploca are able to accumulate nitrate, and the coefficient of nitrate accumulation in wet bacterial mass in relation to the near-bottom water is 1.3 × 10 4 , suggesting a similarity of metabolism with seawater species. A more lightweight isotopic composition of nitrogen in cell mass as compared to that of representatives of zoobenthos also indicates an active metabolism of nitrogen, apparently, in the process of nitrogen respiration. Comparison of the composition of stable isotopes of carbon in the biomass of representatives of different trophic levels, including Thioploca , found at a depth of 105 m indicates its planktonic origin, whereas, in the deeper bay region, the biomass of Thioploca incorporates more of the light carbon originating from biogenic methane.

The biogeochemical processes of methane production and oxidation were studied in the upper horizons of tundra and taiga soils and raised bogs and lake bottom sediments near the Tarko-Sale gas field in western Siberia. Both in dry and water-logged soils, the total methane concentration (in soil particles and gaseous phase) was an order of magnitude higher than in the soil gaseous phase alone (22 and 1.1 nl/cm 3 , respectively). In bogs and lake bottom sediments methane concentration was as high as 11 μl/cm 3 . Acetate was the major precursor of the newly formed methane. The rate of aceticlastic methanogenesis reached 55 ng C/(cm 3 day), whereas that of autotrophic methanogenesis was an order of magnitude lower. The most active methane production and oxidation were observed in bogs and lake sediments, where the δ 13 C values of CO 2 were inversely related to the intensity of bacterial methane oxidation. Methane diffusing from bogs and lake bottom sediments showed δ 13 C values ranging from –78 to –47‰, whereas the δ 13 C value of carbon dioxide ranged from –18 to –1‰. In these ecosystems, methane emission comprised from 3 to 206 mg CH 4 /(m 2 day). Conversely, the dry and water-logged soils of the tundra and taiga took up atmospheric methane at a rate varying from 0.3 to 5.3 mg CH 4 /(m 2 day). Methane consumption in soils was of biological nature. This was confirmed by the radioisotopic method and chamber experiments, in which weighting of methane carbon was observed (the δ 13 C value changed from –51 to –41‰).

The occurrence and activity of sulfate-reducing bacteria were studied in the bottom sediments of Lake Baikal. The number of these bacteria ranged from 500 to 210 000 cells/ml. The rate of sulfate reduction ranged from 0.04 to 38.5 mu g S/(kg day). The highest rates of the process were revealed in littoral sediments rich in allochthonous and autochthonous organic matter.