ИСТИНА

The study of bacterial communities from soils with cryptogamic hypolithic horizons in the ice-free landscapes of the Larsemann and Thala Hills in East Antarctica revealed specific distribution of prokaryotes biomass in the soil microprofiles, and potential viability of prokaryotes cells. It was shown that the number of prokaryotes in studied soils was significantly (by 1-2 orders of magnitude) lower, than in soils of the temperate zone and did not exceed 108 cells in 1 g: maximum values were registered in the upper organogenous horizons and lowest - in the subsoil mineral horizons. The maximum number of bacteria was detected in organogenous horizons (cyanobacteria-algae-moss biocrusts, peaty horizons), and soil horizons formed under the stone pavements. Considerable part of the prokaryotes was represented by filterable forms. The cells revealed different morphology as studied by TEM. It was estimated for the first time that the number and content of filterable forms of prokaryotes (nanobacteria) was rather high in Antarctic soils. The number of such cells ranged from tens to hundreds of millions of cells in 1 g of soil, and their proportion ranged from 5 to 90% of the total population, which is significantly higher than in soils of the temperate zone. FISH method (fluorescence in situ hybridization) revealed that both bacteria of normal size and filterable forms belonged to the same phylogenetic group. The data confirm the assumption of nanotransformation of bacteria in extreme environmental conditions. The study of taxonomic prokaryotic diversity at the level of phyla indicated on the predominance of Bacteria over the Archaea domain. Among the Bacteria domain the phylum Proteobacteria was dominant. The proportion of the phyla Actinobacteria, Planctomycetes, Acidobacteri was lower. Filterable forms belonged to the same phyla. The study of microbial succession, initiated by moistening, showed that the minimum index of the total number of prokaryotes was in the initial (zero) point, and maximum index reached on the 14th day and up to the 60th day, then the number of viable cells gradually declined. In contrast to normal bacterial forms, the maximum index of total number of filterable forms was determined at the starting point of succession, and then declined. This process was accompanied by an increase in the content of larger cells in size, that indicate on appearance of usual bacterial forms. Estimation of the potential biological activity in studied horizons, using gas chromatography methods, showed that indexes of potential activity of nitrogen fixation, denitrification and production of carbon dioxide and methane were lower, than in soils of the temperate zone. The maximum values of those indexes reached in the upper horizons, with high number of viable prokaryotes and abundant growth of cyanobacterial/algal biocrusts. So, studied soils with cryptogamic hypolithic horizons contained niches, which harbored bacterial communities under the stone pavements, playing an important role in the formation of bio-abiotic profiles. This study was funded by the Russian Science Foundation, Project No. 14-50-00029 in the part concerning microbiological study, and the Russian Science Foundation, Project No. 14-27-00133 in the part concerning the selection, description and analysis of the soils, and the Russian Foundation for Basic Research, Project No. 16-04-01776 in the part concerning studies of hypolithic organogenous horizons.