[Diversity and viability of prokaryotes in primitive soils of the larsemann oasis (East Antarctica)]

The diversity and viability of prokaryotic communities in the primitive organomineral soils of East Antarctica have been studied; it has been shown that the total number of bacteria is smaller than and the viability of bacteria is similar to that in soils of the temperate zone. The prokaryotic communities are characterized by the occurrence of a major part of cells in filterable forms, which is higher than the analogous parameter for the temperate soils. The method of fluorescence in situ hybridization (FISH) revealed that the distribution of the main taxons is similar to that in the temperate soils: the portion of the domain Archaea is smaller than that of the domain Bacteria; the total content of Gram-negative bacteria (the phyla Proteobacteria, Acidobacteria, and Planctomycetes) is higher than that of Gram-positive bacteria (Actinobacteria). Within the phylum Proteobacteria, a significant variation of three proteobacterial classes has been noted along the profiles of the soils studied.

[Association of the strA-strB genes with plasmids and transposons in the present-day bacteria and in bacterial strains from permafrost]

Transposons closely related to the streptomycin resistance transposon of modem bacteria, Tn5393, were detected in the bacterial isolates from permafrost resistant to streptomycin. Many transposons studied were located on the medium-size plasmids with a narrow host range. None of the streptomycin-resistant strains isolated from permafrost contained small plasmids carrying the strA-strB genes and related to the broad host range plasmid RSF1010.

[Isolation of antibiotic resistance bacterial strains from East Siberia permafrost sediments]

A collection of bacterial antibiotic resistance strains isolated from arctic permafrost subsoil sediments of various age and genesis was created. The collection included approximately 100 strains of Gram-positive (Firmicutes, Arthrobacter) and Gram-negative bacteria (Bacteroidetes, gamma-Proteobacteria, and alpha-Proteobacteria) resistant to aminoglycoside antibiotics (gentamycin, kanamycin, and streptomycin), chloramphenicol and tetracycline. Antibiotic resistance spectra were shown to differ in Gram-positive and Gram-negative bacteria. Multidrug resistance strains were found for the first time in ancient bacteria. In studies of the molecular nature of determinants for streptomycin resistance, determinants of the two types were detected: strA-strB genes coding for aminoglycoside phosphotransferases and genes aadA encoding aminoglycoside adenylyltransferases. These genes proved to be highly homologous to those of contemporary bacteria.

Microbial populations in Antarctic permafrost: biodiversity, state, age, and implication for astrobiology

Antarctic permafrost soils have not received as much geocryological and biological study as has been devoted to the ice sheet, though the permafrost is more stable and older and inhabited by more microbes. This makes these soils potentially more informative and a more significant microbial repository than ice sheets. Due to the stability of the subsurface physicochemical regime, Antarctic permafrost is not an extreme environment but a balanced natural one. Up to 10(4) viable cells/g, whose age presumably corresponds to the longevity of the permanently frozen state of the sediments, have been isolated from Antarctic permafrost. Along with the microbes, metabolic by-products are preserved. This presumed natural cryopreservation makes it possible to observe what may be the oldest microbial communities on Earth. Here, we describe the Antarctic permafrost habitat and biodiversity and provide a model for martian ecosystems.

[Endospore formation by Streptomyces avermitilis in submerged culture]

The capability of streptomycetes to form endospores during their life cycle was studied in submerged cultures of Streptomyces avermitilis. Submerged S. avermitilis spores were most intensely formed (1) during the culture development cycles on synthetic medium CP1 with glucose under phosphate limitation, and (2) in autolysing cell suspensions of high density obtained by tenfold concentration of a stationary-phase culture grown in a synthetic medium resuspended in phosphate buffer (pH 7.2) with 0.2% CaCl2. Endospores of S. avermitilis formed in submerged cultures shared the major characteristics of specialized microbial resting forms: heat resistance, resistance to lysozyme, ability to pertain to the main species-defining features, and ultrastructural organization characteristic of endospores. They can be considered a resting form of streptomycetes alternative to the spores formed exogenously on aerial mycelium in a surface culture.

[Resting forms of gram negative chemolithoautotrophic bacteria Thioalkalivibrio versutus and Thioalkalimicrobium aerophilum]

The haloalkaliphilic chemoautotrophic gram-negative bacteria Thioalkalivibrio versutus, strain AL2, and Thioalkalimicrobium aerophilum, strain AL3, were shown to possess the capacity to produce resting forms, namely cyst-like refractile cells (CRC), whose production was controlled by the level of the d1 extracellular factors, exhibiting the function of anabiosis autoinducers. The conditions were elucidated that promoted the formation of CRC in the developmental cycles of the cultures studied, in condensed cell suspensions undergoing autolysis, and under the action of exogenously introduced chemical analogues of anabiosis autoinducers (alkylhydroxybenzenes). The peculiarities of the fine structure of the resting cells obtained were studied. Distinctions were revealed (with respect to viability and thermotolerance) between the CRC formed under different conditions. The relationship between the growth strategy and survival strategy of extremophilic bacteria is discussed with taking into account the effect of the d1 autoregulatory factors. A new model of CRC formation is proposed: CRC production in the life cycle of bacteria developing under conditions of increased concentration of anabiosis autoinducers.

[Mercury-resistant bacteria from permafrost sediments and prospects for their use in comparative studies of mercury resistance determinants]

Mercury-resistant bacteria were isolated from permafrost sediments of Kolyma lowland and Canada existing over five thousand to two million years. Their content was shown to vary within the range 0.001-2.9% and to depend on the amount of mercury in sampling sites (coefficient of correlation 0.75). A collection of mercury-resistant bacterial strains was created. In this collection, various representatives of both Gram-positive bacteria (Bacillus, Exiguobacterium, Micrococcus, Arthrobacter) and Gram-negative bacteria (Pseudomonas, Acinetobacter, Plesiomonas, Myxobacteriales) were identified. Most resistant bacteria were found to contain determinants homologous to mer-operons of contemporary bacteria. The isolated strains of paleobacteria are proposed to be used for a comparative structural study of contemporary and ancient plasmids and transposons carrying mercury resistance determinants.

[Synthesis of anabiosis autoinducers in non-spore-forming bacteria as a mechanism regulating their activity in soil and subsoil sedimentary rocks]

Non-spore-forming bacteria of the genera Arthrobacter and Micrococcus, isolated from permafrost subsoil, were found to produce greater amounts of the d1 extracellular factor than closely related collection strains isolated from soil. The effect of this factor, responsible for cell transition to anabiosis, was not species-specific. Thus, the d1 crude preparation isolated from the culture liquid of the permafrost isolate Arthrobacter globiformis 245 produced an effect on the collection strain Arthrobacter globiformis B-1112 and also on Micrococcus luteus and Bacillus cereus. The crude d1 preparation from the permafrost isolate of Arthrobacter differed from the chemical analogue of this factor, 4n-hexylresorcinol, in the level of the induced cell response, which may have resulted from different cell sensitivity to various homologs of alkylhydroxybenzenes contained in the d1 preparation. Thus, additional evidence was obtained indicating that autoregulation of bacterial growth and development is implemented at the level of intercellular interactions in microbial communities. Abundant production of the d1 anabiosis-inducing factors by bacteria isolated from permafrost subsoil is probably a result of special antistress mechanisms responsible for the survival of these bacteria under extreme conditions of natural deep cooling.

[Formation of resting forms of Arthrobacter globiformis in autolysing cell suspensions]

Under conditions of spontaneous or induced autolysis of thick cell suspensions, Arthrobacter globiformis strains produced cells exhibiting features typical of resting microbial forms. The number of viable resting cells was greater under conditions of induced rather than spontaneous autolysis. The thermoresistance of the resting cells of A. globiformis strains isolated from 2- to 3 million-year-old permafrost was higher than that of the collection A. globiformis strain.

[Reproductive resting forms of Arthrobacter globiformis]

Submerged cultures of Arthrobacter globiformis grown in media unbalanced with respect to carbon and nitrogen sources were found to contain cells exhibiting features typical of resting forms: long-term viability, specific ultrastructure, dormant metabolism, and thermoresistance. Such cells were produced not only in the collection strain VKM B-1112, but also in the A. globiformis strains isolated from 2- to 3-million-year-old permafrost sediments.

Preservation of cell structures in permafrost: a model for exobiology

The present report is the first contribution toward a comprehensive fine-structural study of microbial cells from permafrost. Prokaryotes with a variety of cell wall types demonstrate high stability of cell structure after long-term cryopreservation in frozen soils and sediments of the Arctic. The surface capsular layers that were a salient feature of the cells both in situ and on nutrient media may be an adaptation to low temperature. To the extent that permafrost regions on Earth approximate Martian conditions, preservation of cell structure there can serve as the basis for predictions about preservation in Martian permafrost sediments.

[Extracellular alkaline ribonucleases produced by Bacilli strains from the permafrost of the Kolyma lowland]

Aerobic spore-forming bacteria were isolated from the permafrost of the Kolyma lowland. Two strains of bacilli are shown to produce a relatively large amount of extracellular low-molecular weight alkaline RNases. The N-terminal amino acid sequences of the RNases secreted by these strains are similar. This suggests that the protein sequences of the RNases of Bacillus species have been conserved in the course of evolution.

Cryoprotective properties of water in the Earth cryolithosphere and its role in exobiology

In permanently frozen rocks, water occurs in all the three phases and plays a dual role from the biological point of view. About 93-98% of it is in the solid state. This, alongside with negative temperatures, contributes to cell cryoconservation. The remaining 2-7% is in the unfrozen state and represents thin films enveloping organic-mineral particles. These films play the role of cryoprotectors against cell damage by ice crystals during geologically significant time. Electron microscope examinations of prokaryotes revealed the well preserved outer cell structures, specifically strong envelopes and capsules. The cells are resistant to water phase transitions through 0 degrees C, i.e. to the freezing-thawing stress. The exobiological implication of this phenomenon is determined by the fact that the Earth permafrost at first approximation can he considered as a model of e.g. the Mars one. The latter protects the cells against radiation and simultaneously serves as a cryoconservant. However, most important is the possible presence of unfrozen (= liquid) water as prerequisite for the development of microbial life forms.

[Comparative electron microscopic study of cultures of Nocardia asteroides and of the Nocardia-like variant, Actinomyces chrysomallus]

The ultrastructural organization of the red-orange cultures of Nocardia (Proactinomyces) asteroides was compared with that of a Nocardia-like variant of Actinomyces (Streptomyces) chrysomallus isolated upon the inoculation of the submerged parent culture. The comparison has demonstrated for the first time that the major difference consists in the structure of their cross partitions. In Nocardia, the septa is split at all stages of its formation; in the Nocardia-like variant, the partitions have the same structure as the cultures of the genus Actinomyces (Streptomyces). Therefore, the accepted terminology is conventional.

Fine structure of vegetative mycelium and spores of Nocardia spp

The fine structure of a fragmenting and sporulating mycelium of cultures of actinomycetes possessing biochemical properties characteristic of the genus Nocardia--a cell wall of type IV and lipid LCN a--was studied. It was found that fragmenting hyphae are similar in structure to the vegetative hyphae of known actinomycetes. Sporulation takes place through the simultaneous division of a sporulating hypha by numerous septa. Spores differ from vegetative cells in the presence of a thickened electron-dense cell wall, dense internal contents, and the presence of vacuoles.

[New elementary structures of actinomycete spores of the genera Actinomadura and Streptomyces]

The structure of spore surfaces was studied by electron microscopy in five species of actinomycetes, and two new types of elementary surface structures were discovered. The surface of spores in Streptomyces regensis consists of long flexible, closely interwoven, band-like structures 25 A wide. Ring-like structures 140--150 A in diameter can be observed on spores of Actinomadura verrucosospora; their clusters resemble grapes and the spore silhouette looks like a cone. Rod-like structures of spores in Streptomyces cavourensis and Str. streptomycini which form an ornament resembling the surface of a basket and tubular strucutres in Str. acrimycini of which hair-shaped spore protrusions are made are similar to the elementary structures of spore surfaces in other actinomycetes.

[Electron microscopic study of spore formation in Actinomadura verrucosospora]

The formation of spores was studied with a morphologic type of the Actinomadura genus, Acd. verrucosospora (Nonomura a. Ohara, 1971. Spore formation begins with the division of a hypha by cross-partitions which, as a rule, appear as monolayered on cross-sections, thus differing from sporulation septae found in other actinomycetes. The structure and shape of septae change in the course of spore formation: first, they consist of one layer and have the same thickness as the cell wall; later, they consist of several layers and their thickness is uneven (the shape of dumbbels). In the course of spore maturation, thick regions of the septae are destroyed. Mature spores are characterized by the presence of vacuoles, the thichened cell wall and outer sheath; the latter bears rounded structures arranged in conglomerates which resemble grapes. The process of sporogenesis and the structure of spores in Actinomadura verrucosospora differ from those in other species of the Actinomadura genus (Williams et al., 1974; Soina et al., 1975); therefore, this genus of actinomycetes is heterogenous.

[Fine structure of the vegetative and spore-forming hyphae of Micropolyspora fascifera]

Changes in the fine structure of the hyphae were studied in the course of spore formation by Micropolyspora fascifera. Sporulating hyphae differ from vegetative hyphae by a less dense cytoplasm, a large zone of the nucleoid with distinctly fibrillar structure, and a thin layerless cell wall. Spore formation is accompanied with autolysis of the vegetative hyphae, which consists in vacuolization of the hyphae and appearance of a large number of tubular membrane structures within them. Spores are formed, like in Actinomyces spp., by simultaneous division of the hyphae with septa; the structure of sporulating septa is similar to that of the fragmenting mycelium in Nocardia; the structure of mature spores is similar to that in some Actinomyces spp. Therefore, M. fascifera differs from other Micropolyspora spp. not only by the chemical composition of the cells (the presence of nocardiomicolic acids) but also by their structure. Taxonomic position of the species is discussed.

[Ultrastructure of the mycelium and spores of Actinomadura fastidiosa sp. nov]

A new species of the Actinomadura genus, A. fastidiosa sp. nov., is described. The ultrastructure of the vegetative mycelium and spores of this organism was studied. The vegetative cells have a multilayered cell wall, often consisting of five layers with different thickness and electron density. The spores are similar to the vegetative cells by their inner structure but have a thicker wall.