[Colorless sulfur bacteria Thioploca from different sites in Lake Baikal].

The colorless sulfur bacteria Thioploca spp. found in Lake Baikal are probably a marker for the influx of subterranean mineralized fluids. Bacteria act as a biological filter; by consuming sulfide in their metabolism, they detoxicate it and maintain the purity of Lake Baikal's water. The bacteria were investigated by various techniques. According to analysis of the 16S rRNA gene fragment, Thioploca sp. from Frolikha Bay, Baikal belongs to the clade of freshwater species found in Lake Biwa and Lake Constance; it is most closely related to Thioploca ingrica.

[Thiobacillus sajanensis sp. nov., a new obligately autotrophic sulfur-oxidizing bacterium isolated from Khoito-Gol hydrogen-sulfide springs, Buryatia].

Four strains of rod-shaped gram-negative sulfur-oxidizing bacteria were isolated from Khoito-Gol hydrogen-sulfide springs in the eastern Sayan Mountains (Buryatia). The cells of the new isolates were motile by means of a single polar flagellum. The strains were obligately chemolithoautotrophic aerobes that oxidized thiosulfate (with the production of sulfur and sulfates) and hydrogen sulfide. They grew in a pH range of 6.8-9.5, with an optimum at pH 9.3 and in a temperature range of 5-39 degrees C, with an optimum at 28-32 degrees C. The cells contained ubiquinone Q-8. The DNA G+C content of the new strains was 62.3-64.2 mol %. According to the results of analysis of their 16S rRNA genes, the isolates belong to the genus Thiobacillus within the subclass Betaproteobacteria. However, the similarity level of nucleotide sequences of the 16S rRNA genes was insufficient to assign the isolates to known species of this genus. The affiliation to the genus Thiobacillus was confirmed by DNA-DNA hybridization of the isolates with the type strain of the type species of the genus Thiobacillus, T. thioparus DSM 505T (= ATCC 8158T). Despite the phenotypic similarity, the hybridization level was as low as 21-29%. In addition, considerable differences were revealed in the structure of the genes encoding RuBPC, the key enzyme of autotrophic CO2 assimilation, between the known Thiobacillus species and the new isolates. Based on molecular-biological features and certain phenotypic distinctions, the new isolates were assigned to a new Thiobacillus species, T. sajanensis sp. nov., with the type strain 4HGT (= VKM B-2365T).

[Carbon and sulfur metabolism in representatives of two clusters of bacteria of the genus Leucothrix: a comparative study]. / Sravnitel'naia kharakteristika uglerodnogo i sernogo metabolizma u predstavitelei dvukh klasterov bakterii roda Leucothrix.

Major pathways of carbon and sulfur metabolisms were studied in representatives of two clusters of bacteria: Leucothrix thiophila (cluster I, strains 2WS, 4WS, and 6WS) and Leucothrix sp. (cluster II, strains 1WS, 3WS, and 5WS). All strains were capable of chemoorganoheterotrophic growth, as well as of chemolithoheterotrophic growth in the presence of reduced sulfur compounds. The bacteria were found to possess a complete set of the enzymes of the tricarboxylic acid cycle and glyoxylate cycle. The hydrogenase activity in cells of cluster I strains was an order of magnitude lower than in cluster II strains and in other known heterotrophic bacteria. Cells of bacteria of both clusters exhibited high activity levels of enzymes involved in the energy metabolism of sulfur. The oxidation of sulfur compounds and the operation of the electron-transport chain were shown to be related. Cluster II bacteria more efficiently use organic compounds in their energy metabolism, whereas cluster I bacteria are characterized by more efficient utilization of reduced sulfur compounds. During sulfite oxidation, cluster I bacteria can synthesize ATP both via substrate-level phosphorylation and oxidative phosphorylation, whereas cluster II bacteria synthesize ATP only via the latter process.

[Ecophysiological features of mat-forming bacteria Thioploca in bottom sediments of Frolikha Bay, northern Baikal]. / Ekofiziologicheskie osobennosti matobrazuiushche bakterii Thioploca v donnykh osadkakh bukhty Frolikha, severnyi Baikal.

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 x 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.