N. A. Manucharova

100 kGy gamma-affected microbial communities within the ancient Arctic permafrost under simulated Martian conditions

This research aimed to investigate the viability and biodiversity of microbial communities within ancient Arctic permafrost after exposure to a gamma-radiation dose of 100xa0kGy at low temperature (−xa050xa0°C), low pressure (1xa0Torr) and dehydration conditions. The main objective was to assess the possibility for long-term survival of Earth-bound microorganisms in the subsurface of Martian regolith or inside small space bodies at constant absorption and accumulation of the gamma radiation dose. Investigated microbial communities had shown high resistance to a simulated Martian environment. After irradiation the total count of prokaryotic cells and number of metabolically active bacterial cells remained at the control level, while the number of bacterial CFUs decreased by 2 orders of magnitude, and the number of metabolically active cells of archaea decreased threefold. Besides, the abundance of culturable bacteria after irradiation was kept at a high level: not less than 3.7xa0×xa0105xa0cells/g. Potential metabolic activity of irradiated microbial communities in general were higher than in the control sample. A fairly high biodiversity of bacteria was detected in the exposed sample of permafrost, although the microbial community structure underwent significant changes after irradiation. In particular, actinobacteria populations of the genus Arthrobacter, which was not revealed in the control samples, became predominant in bacterial communities following the exposure. The results of the study testify that long-term preservation of microbial life inside Martian permafrost is possible. The data obtained can also be evaluated from the perspective of the potential for discovering viable Earth-bound microorganisms on other objects in the Solar system and inside of small bodies in outer space.

Structure of epiphytic bacterial communities of weeds

Dynamics of the taxonomic structure of epiphytic bacterial communities of the rhizosphere and phyllosphere of seven weed species was studied. The major types of isolated organisms were identified using phenotypic and molecular biological approaches. Dispersion analysis revealed that the ontogenesis stage and plant organ were the factors with the greatest effect on the taxonomic structure of the communities. The dominant microorganisms of weeds were similar to those of cultivated plants. The minor components revealed in the spectra of bacterial communities of weeds belonged to poorly studied genera of chemolithotrophic proteobacteria.

The structure and functions of bacterial communities in an agrocenosis

The most significant factor responsible for the specific taxonomic composition of the bacterial communities in the agrocenosis studied was found to be a part or organ of plants (leaves, flowers, roots, fruits). A stage of plant ontogeny also determines changes of taxa. In the course of the plant growth, eccrisotrophic bacteria are replaced by hydrolytic ones that belong to the group of cellulose-decomposing bacteria. Representatives of the proteobacteria genera that are difficult to identify by phenotypic methods were determined using molecular–biological methods. They were revealed only on oat leaves in the moist period. As the vetch–oat mixture was fertilized with BIOUD-1 (foliar application) in the phyllosphere of both oats and vetch, on all the plant organs, representatives of the Rhodococcus genus as dominants were isolated. This fact was related to the capability of bacteria to decompose the complex aromatic compounds that are ingredients of the fertilizers applied. Another positive effect for plants of the bacterial communities forming in agrocenoses is the presence of bacteria that are antagonists of phytopathogenic bacteria. Thus, in agrocenoses, some interrelationships promoting the growth and reproduction of plants are formed in crop plants and bacteria.

Filamentous actinobacteria of the saline soils of arid territories

A large number of actinomycetes (hundreds, thousands, and millions of CFU/g of soil) were isolated from saline soils in the territory of the landscapes of the Ber hillocks. A significantly smaller quantity of actinomycetes was isolated from the soda saline soils and sor saline soils that formed at the bottom of the ephemeral salty lakes in Buryatiya and in the estuary of the Syr-Darya River. Actinomycetes were represented in the studied soils by the Streptomyces, Micromonospora, Actinomadura, and Nocardiopsis genera. Among streptomycetes, the species of the Albus section and the Albus series predominated. The activity of the consumption of substrates by cultures of actinomycetes was largely influenced by conditions of preincubation. Obviously, the influence was related to the alteration in the metabolism of actinomycetes as one of the mechanisms of adaptation to the increased osmolarity of environment. The alcalotolerance, thermotolerance, and xerotolerance of halotolerant actinomycetes of the saline soils of arid territories were experimentally revealed.

Description of the Phylogenetic Structure of Hydrolytic Prokaryotic Complex in the Soils

With the help of the molecular-biological method of cell hybridization in situ (FISH), the abundance of a physiologically active hydrolytic prokaryotic complex in chernozem and gley-podzolic soils is determined. The total proportion of metabolically active cells, which were detected by hybridization with universal probes as representatives of the domains Bacteria and Archaea, in samples of the studied soil, was from 38% for chernozem up to 78% for gley-podzolic soil of the total number of cells. The differences in the structure of chitinolytic and pectinolytic prokaryotic soil complexes are detected. Along with the high abundance of Actinobacteria and Firmicutes in the soils with chitin, an increase in phylogenetic groups such as Alphaproteobacteria and Bacteroidetes is observed.

Anaerobic methane oxidation in soils and water ecosystems

The process of anaerobic methane oxidation has been studied for over 30 years on the example of bottom marine sediments and fresh water ecosystems. This paper presents a review of the results of these investigations. It is also demonstrated that this process can proceed not only in submerged but also in drained peat and automorphic sod-podzol soils. The latter soils continue to absorb methane after anaerobic conditions are created and an inhibitor of methane monooxygenase (acetylene) is introduced. Oxidated compounds (nitrates, sulphates) are stimulatory to gas absorption; deoxidated nitrogen compounds (ammonium chloride) do not produce significant changes. Incubation with the addition of nitrates and sulphates in an atmosphere of argon and methane results in an increase in the fraction and abundance of archaea in the soil. This is in agreement with the data obtained for aquatic inhabits.

Microbial activity in Martian analog soils after ionizing radiation: implications for the preservation of subsurface life on Mars

At present, the surface of Mars is affected by a set of factors that can prevent the survival of Earth-like life. However, the modern concept of the evolution of the planet assumes the existence more favorable for life climate in the past. If in the past on Mars had formed a biosphere, similar to the one that originated in the early Earth, it is supposed that it is preserved till now in anabiotic state in the bowels of the planet, like microbial communities inhabiting the ancient permafrost of Arctic and Antarctic. In the conditions of modern Martian regolith, this relic life seems to be deprived of the possibility of damage reparation (or these processes occur on a geological time scale), and ionizing radiation should be considered the main factor inhibiting such anabiotic life. In the present study, we studied soil samples, selected in two different extreme habitats of the Earth: ancient permafrost from the Dry Valleys of Antarctica and Xerosol soil from the mountain desert in Morocco, gamma-irradiated with 40 kGy dose at low pressure (1 Torr) and low temperature (−50 °C). Microbial communities inhabiting these samples showed in situ high resistance to the applied effects, retained high number of viable cells, metabolic activity, and high biodiversity. Based on the results, it is assumed that the putative biosphere could be preserved in the dormant state for at least 500 thousand years and 8 million years in the surface layer of Mars regolith and at 5 m depth, respectively, at the current level of ionizing radiation intensity.

Absolute number of Bacteria and Archaea in soil

The possibility of using the method of exhaustion (removal sampling) applied to determine the absolute number of Bacteria and Archaea populations in soil based on accounting data for quantitative fluorescence in situ hybridization has been shown.

Ecological and Taxonomic Features of Actinomycetal Complexes in Soils of the Lake Elton Basin

In the sor (playa) solonchaks of chloride and sulfate–chloride salinity (the content of readily soluble salts is 0.9–1.0%) in the delta of the Khara River discharging into Lake Elton, the number of mycelial actinobacteria (actinomycetes) is low ((2–3) × 103 CFU/g of soil). At a distance from the water’s edge, these soils are substituted for the light chestnut ones, for which an elevated number of actinomycetes (an order of magnitude higher than in the sor solonchaks) and a wider generic spectrum are characteristic. The actinomycetal complex is included the Streptomyces and Micromonospora genera, whereas in the sor solonchaks around the lake, representatives of Micromonospora were not found.

Effect of potassium chloride on the emission of carbon dioxide from chernozem

The dynamics of carbon dioxide emission from the soil is traced over nine months by the method of microbial succession initiation for characterizing the microbial activity of soil. A twofold decrease of carbon dioxide emission from the fertile chernozem is observed when potassium chloride is used as a fertilizer. The contents of available nitrogen and especially phosphorus decrease in a pot experiment with barley at standard rates of fertilizer application. The reduction in the content of soluble salts (primarily chlorides and nitrates) in the nonsaline soil after leaching increases the microbial activity.