E. I. Kompantseva

Thiorhodospira sibirica gen. nov., sp. nov., a new alkaliphilic purple sulfur bacterium from a Siberian soda lake.

A new purple sulfur bacterium was isolated from microbial films on decaying plant mass in the near-shore area of the soda lake Malyi Kasytui (pH 9.5, 0.2% salinity) located in the steppe of the Chita region of south-east Siberia. Single cells were vibrioid- or spiral-shaped (3-4 microns wide and 7-20 microns long) and motile by means of a polar tuft of flagella. Internal photosynthetic membranes were of the lamellar type. Lamellae almost filled the whole cell, forming strands and coils. Photosynthetic pigments were bacteriochlorophyll a and carotenoids of the spirilloxanthin group. The new bacterium was strictly anaerobic. Under anoxic conditions, hydrogen sulfide and elemental sulfur were used as photosynthetic electron donors. During growth on sulfide, sulfur globules were formed as intermediate oxidation products. They were deposited outside the cytoplasm of the cells, in the peripheral periplasmic space and extracellularly. Thiosulfate was not used. Carbon dioxide, acetate, pyruvate, propionate, succinate, fumarate and malate were utilized as carbon sources. Optimum growth rates were obtained at pH 9.0 and optimum temperature was 30 degrees C. Good growth was observed in a mineral salts medium containing 5 g sodium bicarbonate l-1 without sodium chloride. The new bacterium tolerated up to 60 g sodium chloride l-1 and up to 80 g sodium carbonates l-1. Growth factors were not required. The DNA G + C composition was 56.0-57.4 mol%. Based on physiological, biochemical and genetic characteristics, the newly isolated bacterium is recognized as a new species of a new genus with the proposed name Thiorhodospira sibirica.

Heliorestis daurensis, gen. nov. sp. nov., an alkaliphilic rod-to-coiled-shaped phototrophic heliobacterium from a Siberian soda lake

Abstract A novel alkaliphilic heliobacterium was isolated from microbial mats of a low-salt alkaline Siberian soda lake. Cells of the new organism were tightly coiled when grown in coculture with a rod-shaped bacterium, but grew as short filaments when finally obtained in pure culture. The new phototroph, designated strain BT-H1, produced bacteriochlorophyll g and a neurosporene-like pigment, and lacked internal photosynthetic membranes. Similar to other heliobacteria, strain BT-H1 grew photoheterotrophically on a limited range of organic compounds including acetate and pyruvate. Sulfide was oxidized to elemental sulfur and polysulfides under photoheterotrophic conditions; however, photoautotrophic growth was not observed. Cultures of strain BT-H1 were alkaliphilic, growing optimally at pH 9, and unlike other heliobacteria, they grew optimally at a temperature of 25 °C rather than at 40 °C or above. Analysis of the 16S rRNA gene sequence of the new organism showed that it groups within the heliobacterial clade. However, its branching order was phylogenetically basal to all previously investigated species of heliobacteria. The G+C content of the DNA of strain BT-H1 (44.9 mol%) was also quite distinct from that of other heliobacteria. This unique assemblage of properties implicates strain BT-H1 as a new genus and species of the heliobacteria, Heliorestis daurensis, named for its unusual morphology (“restis” is Latin for “rope”) and for the Daur Steppe in Russia in which these soda lakes are located.

Rhodovulum steppense sp. nov., an obligately haloalkaliphilic purple nonsulfur bacterium widespread in saline soda lakes of Central Asia.

Seven strains of purple nonsulfur bacteria isolated from the shallow-water steppe soda lakes of the cryoarid zone of Central Asia formed a genetically homogeneous group within the genus Rhodovulum. The isolates were most closely related to Rhodovulum strictum, from which they differed at the species level (99.5 % 16S rRNA gene identity and 42-44 % DNA-DNA hybridization level). According to genotypic and phenotypic characteristics, the strains were assigned to a new species of the genus Rhodovulum, for which the name Rhodovulum steppense sp. nov. is proposed. Cells of all strains were ovoid to rod-shaped, 0.3-0.8 microm wide and 1-2.5 microm long, and motile by means of polar flagella. They contained internal photosynthetic membranes of the vesicular type and photosynthetic pigments (bacteriochlorophyll a and carotenoids of the spheroidene series). All strains were obligate haloalkaliphiles, growing within a wide range of salinity (0.3-10 %) and pH (7.5-10), with growth optima at 1-5 % NaCl and pH 8.5. Photo- and chemoheterotrophic growth occurred with a number of organic compounds and biotin, thiamine and niacin as growth factors. No anaerobic respiration on nitrite, nitrate or fumarate and no fermentation was demonstrated. Bacteria grew photo- and chemolithoautotrophically with sulfide, sulfur and thiosulfate, oxidizing them to sulfate. Sulfide was oxidized via deposition of extracellular elemental sulfur. No growth with H(2) as electron donor was demonstrated. The major fatty acid was 18 : 1 (81.0 %). The major quinone was Q-10. The DNA G+C content was 66.1 mol% (T(m)). The type strain, A-20s(T) (=VKM B-2489(T) =DSM 21153(T)), was isolated from soda lake Khilganta (Zabaikalskii Krai, southern Siberia, Russia).

Zeta potential of anoxygenic phototrophic bacteria and Ca adsorption at the cell surface: Possible implications for cell protection from CaCO3 precipitation in alkaline solutions

Electrophoretic mobility measurements and surface adsorption of Ca on living, inactivated, and heat-killed haloalkaliphilic Rhodovulum steppense, A-20s, and halophilic Rhodovulum sp., S-17-65 anoxygenic phototrophic bacteria (APB) cell surfaces were performed to determine the degree to which these bacteria metabolically control their surface potential equilibria. Zeta potential of both species was measured as a function of pH and ionic strength, calcium and bicarbonate concentrations. For both live APB in 0.1M NaCl, the zeta potential is close to zero at pH from 2.5 to 3 and decreases to -30 to -40 mV at pH of 5-8. In alkaline solutions, there is an unusual increase of zeta potential with a maximum value of -10 to -20 mV at a pH of 9-10.5. This increase of zeta potential in alkaline solutions is reduced by the presence of NaHCO(3) (up to 10 mM) and only slightly affected by the addition of equivalent amount of Ca. At the same time, for inactivated (exposure to NaN(3), a metabolic inhibitor) and heat-killed bacteria cells, the zeta potential was found to be stable (-30 to -60 mV, depending upon the ionic strength) between pH 5 and 11 without any increase in alkaline solutions. Adsorption of Ca ions on A-20s cells surface was more significant than that on S-17-65 cells and started at more acidic pHs, consistent with zeta potential measurements in the presence of 0.001-0.01 mol/L CaCl(2). Overall, these results indicate that APB can metabolically control their surface potential to electrostatically attract nutrients at alkaline pH, while rejecting/avoiding Ca ions to prevent CaCO(3) precipitation in the vicinity of cell surface and thus, cell incrustation.

The structure of phototrophic communities of soda lakes of the southeastern Transbaikal region

The structure of benthic phototrophic communities of 24 soda lakes of the southeastern Transbaikal Region was studied. The physicochemical properties of the lakes were determined. The results of enumeration of anoxygenic phototrophic bacteria (APB) belonging to various groups are presented. The influence of salinity on the structure of APB communities was investigated. The APB reaction to environmental conditions was determined. Massive development of phototrophic microorganisms in the form of mats and films was observed in the majority of the investigated lakes. The APB communities were characterized by a wide diversity and evenness of species composition. Purple sulfur bacteria of the families Ectothiorhodospiraceae and Chromatiaceae were predominant. Purple nonsulfur bacteria of the family Rhodobacteraceae, green filamentous bacteria Oscillochloris sp., and heliobacteria were also detected. According to preliminary data, no less than 15 species of APB occur in the studied lakes. Among them, three novel genera and four species have already been described. Identification of other isolates is still in progress. The lakes make an almost continuous series of fresh, brackish, and saline water bodies, varying in their degree of mineralization. It was demonstrated that the structure of APB communities was unaffected by changes in salinity from 5 to 40 g/l. At salt concentrations of lower than 5 g/l, the level of water mineralization became a limiting factor. Experiments with the isolated cultures showed that the APB were obligately dependent on the presence of carbonate ions in the medium. They were haloalkalitolerant or haloalkaliphilic. Thus, they are well adapted to the conditions of soda lakes with a low of moderate mineralization. It was demonstrated that soda lakes of the southeastern Transbaikal Region represent a special type of habitat which harbors a peculiar autochthonous microflora and differs from both highly mineralized soda lakes and shallow saline water bodies of the sea origin.

Communities of anoxygenic phototrophic bacteria in the saline soda lakes of the Kulunda steppe (Altai Krai)

The saline soda lakes of the Kulunda steppe (Altai krai) are small and shallow; they are characterized by a wide range of salinity and alkalinity, as well as by the extreme instability of their water and chemical regimes. Accumulations of anoxygenic phototrophic bacteria (APB) visible to the unaided eye were noted only in several lakes with high rates of sulfate reduction in their bottom sediments. However, enumeration of APB cells by inoculation revealed their presence in all 17 lakes. APB cell numbers varied from 103 to 109 CFU cm−3. In the APB communities of all lakes, purple sulfur bacteria of the family Ectothiorhodospi- raceae were predominant. In 14 out of the 17 lakes, purple nonsulfur bacteria of the family Rhodobacteraceae were also detected (103–107 CFU cm−3). Purple sulfur bacteria of the family Chromatiaceae were less abundant: Halochromatium sp. (104–107 CFU cm−3) were found in six lakes, while Thiocapsa sp. (104 CFU cm3) were detected in one lake. On the whole, the APB communities of the soda lakes of the Kulunda steppe were characterized by the low diversity and evenness of their species compositions, as well as by the pronounced dominance of the members of the family Ectothiorhodospiraceae. There was no correlation between the structures of the APB communities and alkalinity. However, the dependence of the species composition of APB (mainly ectothiorhodospiras) on water mineralization was revealed. High mineralization (above 200 g l−1) was a limiting factor that affected the APB communities on the whole, restricting the APB species diversity to extremely halophilic bacteria of the genus Halorhodospira.

Purple nonsulfur bacteria in weakly and moderately mineralized soda lakes of the southern Transbaikal Region and northeastern Mongolia

Purple nonsulfur bacteria (PNB) are shown to be widespread in weakly and moderately mineralized soda lakes of the southern Transbaikal Region and northeastern Mongolia. PNB occurred in most samples and enrichments at all pH and salinity values recorded or tested. Of the 24 investigated lakes of the southern Transbaikal Region, they were found in 22. In addition, the presence of PNB was noted in most soda lakes of northeastern Mongolia with water mineralization from 3 to 60 g/l. In all of the lakes, PNB were represented by morphologically similar forms. These were motile rods measuring 0.3–0.5 × 1.2–2.5 μm, multiplying by binary fission and containing bacteriochlorophyll a and carotenoids of the spheroidene series. 17 pure cultures of PNB were isolated from soda lakes of Chita Oblast, Buryat Republic, Agin Buryat Autonomous District, and northeastern Mongolia. All isolates were weakly halophilic and alkaliphilic and grew in wide ranges of salinity (0.3–15%) and pH (7.5–9.5). The highest growth rate was recorded at a 1–3% salinity and a pH value of about 8.5. The bacteria failed to grow in freshwater medium or at pH 7. All of the isolates were assigned to the genus Rhodovulum according to their morphological and physiological properties. For more precise identification of the new isolates, their phylogenetic analysis was performed. According to the results of 16S rRNA gene sequencing and DNA-DNA hybridization, the isolates were most close to the species Rhodovulum strictum, from which they however differed at the species level (98.5–99.5% 16S rRNA gene identity and 42–44% DNA-DNA hybridization level). Moreover, the isolates fell into two groups, one of which was comprised by strain A-20s and its close relatives (100% 16S rRNA identity and 93–98% DNA-DNA hybridization level), and the other was represented by the phylogenetically distinct strain A-36s (98.7% 16S rRNA identity and 50–55% DNA-DNA hybridization level). In the nucleotide sequences of the 16S rRNA genes, sequence signatures were revealed that were specific to the isolates and the two closest species and distinguished them from other Rhodovulum representatives. Thus, the new PNB isolates represent two new species. Currently, their morphological and physiological investigation is in progress, aiming at their description as two new species of the genus Rhodovulum. The fact that PNB of weakly and moderately mineralized soda lakes are represented by new species is one more piece of evidence in favor of our earlier conclusion about the specificity of these habitats and of the autochthonous microflora characteristic of them.

Comparative study of the fatty acid composition of some groups of purple nonsulfur bacteria

The fatty acid composition (FAC) of 43 strains of purple nonsulfur bacteria belonging to six genera—Rubrivivax, Rhodopseudomonas, Rhodoplanes, Blastochloris, Rhodobium, and Rhodomicrobium—was studied by capillary gas chromatography. The cultures were grown on standard medium under standard conditions. Automatic identification of the fatty acid methyl esters and statistical processing of the results were performed by the computerized Microbial Identification System (MIS). Significant differences between the FACs of different genera, species, and, sometimes, strains were revealed. 16S rRNA genes of some of the new isolates, primarily those having a specific FAC, were sequenced. The taxonomic status of a number of the strains in question was determined using the FAC characteristics as one of the criteria. It was shown that the FAC characteristics may be used both for affiliating isolates to known species and for revealing new taxa.

Primary production of organic matter and phototrophic communities in the soda lakes of the Kulunda steppe (Altai krai)

The rates of photosynthesis and dark CO2 fixation were determined in 12 soda lakes of the Kulunda steppe. Characterization of the phototrophic communities was given, and the cell numbers of anoxygenic phototrophic bacteria (APB) were determined. The photosynthetic production in different lakes was substantially different, constituting from 0.01 to 1.32 g C m−2 day−1. The main part of carbon dioxide was assimilated in the process of oxygenic photosynthesis. Anoxygenic photosynthesis was recorded only in 5 of the 12 lakes studied. Its values varied between 0.06 and 0.42 g C m−2 day−1, constituting from 8 to 34% of the total photosynthetic activity. Anoxygenic photosynthesis was revealed in the lakes where the number of APB reached 107–109 CFU cm−3. Dark CO2 fixation constituted 0.01–0.15 g C m−2 day−1. Positive correlation was observed between the primary production value and water alkalinity. No relationship between productivity and water mineralization was revealed in the 30–200 g l−1 range, whereas an increase in salinity above 200 g l−1 suppressed the photosynthetic activity. The mechanisms of influence of the environmental factors on the rate of photosynthesis are discussed.

Interaction of the haloalkaliphilic purple bacteria Rhodovulum steppense with aluminosilicate minerals

The interaction was investigated between the haloalkaliphilic nonsulfur purple bacteria Rhodovulum steppense A-20sT and layered aluminosilicates: micas (biotite, phlogopite, and muscovite) and clay minerals (montmorillonite and kaolinite). The interaction between all components of this system (minerals, water, medium, and bacteria) resulted in the changes in the chemical composition of the minerals and solutions. These changes were especially significant in the presence of bacteria. By using some elements for growth and promoting their transfer into the exchange pool of the minerals, bacteria removed these elements from the medium. The content of exchange bases in the aluminosilicates incubated in the presence of bacteria was several times higher than in the minerals incubated in sterile medium. The observed saturation of the mineral phase with potassium and magnesium may be considered the initial phase of diagenesis of the aluminosilicates under study.