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DPA membranes from Allochromatium vinosum cells, in which carotenoid biosynthesis was inhibited using diphenylamine (DPA) were obtained, into which rhodopin was incorporated. The LH2 complex with rhodopin content of 85% was isolated. Using a test for the thermal stability of LH2 complexes (DPA and with incorporated rhodopin), it was established that carotenoids of the early stages of biosynthesis (≤1 molecules per complex) did not interfere with rhodopin incorporation. It was found that when the LH2 complex with incorporated rhodopin was irradiated with light at the wavelength of 502 nm, BChl850 was photobleached at a rate close to that in the control LH2 complex. This indicates that rhodopin, after being incorporated into the DPA LH2 complex, is capable of generating singlet oxygen under illumination. Previously obtained data on heterogeneity of the carotenoid composition in DPA LH2 complexes (variation in the number of individual carotenoids molecules per complex in the general population) and our earlier suggestion about the structural role of carotenoids, namely, their ability to stabilize the LH2 complexes, were confirmed. Based on analysis of our results, as well as of the literature data, the interaction of singlet oxygen and carotenoids is discussed. [ABSTRACT FROM AUTHOR]

The relic Lake Mogilnoe, separated from the Barents Sea by a sand and pebble dam, is located in the high Arctic on the Kildin island (Murmansk region). This lake is a classic example of a meromictic basin of marine origin. The data obtained during the 2018 expedition showed changes in the hydrochemical regime of the lake that have occurred over the past 20 years. Sulfide concentration in the monimolimnion of the lake was as high as 140 mg/L. A tendency for salinization of the surface waters to 7 g/L has been noted. The Lake Mogilnoe is characterized by a discrepancy between the halocline and thermocline levels. The chemocline zone in the lake is below the halocline level. In a narrow oxygen-containing layer between 3 and 7.5 m, aerobic microflora of the marine type and marine fauna were present. The bacterial plate was formed at the boundary of the sulfide layer at ~8 m and mainly consisted of green sulfur bacteria (GSB). Brown-colored GSB species containing bacteriochlorophyll e were predominant. The previously formed concept of anaerobic phototrophic bacteria (APB) biodiversity based on morphological characteristics was modified using metagenomic data obtained by analyzing DNA from two samples of lake water in the chemocline zone, and was also supplemented by identifying new GSB species. Molecular diagnostic data confirmed the absolute dominance of the brackish species of GSB Chlorobium phaeovibrioides. This is the first isolation and identification of brown- and green-colored Prosthecochloris aestuarii morphotypes from Lake Mogilnoe, as well as of bacteriochlorophyll c-containing Prosthecochloris sp. The taxonomic position of Pelodyction phaem, which was constantly present in the Lake Mogilnoe, is discussed in detail. Despite the partial isolation of the ecosystem of Lake Mogilnoe from the Barents Sea, the main properties of the dominant GSB species and Prosthecochlori aestuarii turned out to be similar to those of the phylotypes living in lakes on the White Sea coast. [ABSTRACT FROM AUTHOR]

Formation of the Kanda Bay resulted from construction of a railway dam (1916) and subsequent isolation of the sea lagoon from the main basin of the Kandalaksha Gulf, White Sea. Decreased action of tidal flows, which mix the water column of the lagoon, altered the hydrological regime of the basin. Decreased water exchange resulted in formation of oxygen-depleted near-bottom water and to sulfide contamination. A freshwater lake was, however, preserved in the southern part of the Kanda Bay. The composition of microbial communities was studied for the near-bottom water horizons at different sides of the Kanda Bay. The oxygen regime in this layer was found to change, with increasing concentrations of sulfide and methane and active processes of sulfate reduction and methane oxidation. The composition of the microbial community changed noticeably, with lower abundance of true marine and freshwater microorganisms and development of bacteria and archaea predominant in microbial communities of anoxic water in meromictic basins. Among the microbial diversity, indicator species with increased abundance were revealed. These are archaea of the genera Methanoregula and Methanosaeta (phylum Halobacterota). The sulfur cycle microorganisms, which were the indicators of stagnant marine water, included anoxygenic phototrophic bacteria of the class Chlorobia, (Chlorobium phaeovibrioides, Pelodictyon phaeoclathratiforme), Chloroflexi of the genus Chloronema, nonsulfur purple bacteria related to the genus Rhodoferax, colorless sulfur bacteria of the family Beggiatoaceae, and sulfur oxidizers of the genus Thiobacillus. Archaea of the genus Nitrosopumilus (phylum Crenarchaeota) and bacteria of the genus Woeseia may be considered opposites to the indicator microorganisms, since they were found only in the open sea water. In our opinion, stable water exchange through the dam will result in the stable composition of the Kanda Bay microbial community, with only seasonal variations and year-to-year fluctuations. The negative scenario supports prediction of conversion of the Kanda Bay into a stratified basin with anoxic near-bottom water and the microbial community similar to that found in meromictic lakes. [ABSTRACT FROM AUTHOR]

Three karst lakes were investigated in the Nizhny Novgorod region: Staropustynskie lakes Svyato and Nekrasov Bay and Lake Svetloyar. The studied lakes belonged to the mesotrophic-eutrophic polyhumous type and were characterized by stable stratification with signs of meromixis. Their water columns were divided into aerobic and anaerobic zones, with the bottom water containing sulfide. Fe(II) compounds were also present in the Staropustynskie lakes. In the Lake Nekrasov Bay, the mixolimnion showed a high rate of oxygenic photosynthesis, up to 1.2 µg С L–1 day–1, as well as a maximum of anoxygenic photosynthesis in the chemocline (0.030–0.706 µg С L–1 day–1) at a depth of 1.5−2.5 m. The peak of dark CO2 assimilation (0.146 µg С L–1 day–1) occurred at a depth of 1.5 m in the oxycline zone. Anoxygenic phototrophic bacteria (APB) were found in the Lakes Nekrasov Bay and Svyato at the boundary of light penetration. Green sulfur bacteria with short cell prosthecate outgrowths, "Ancalochloris sp.," predominated. Consortia "Chlorochromatium aggregatum" and filamentous chlorobacteria "Chloronema giganteum" were also found, their cell sheaths accumulated ferric iron salts. In the Staropustynskie lakes, various morphotypes of iron bacteria formed clusters in the microaerobic zone. In Lake Svetloyar the chemocline was located at a depth of 16 m, outside the photic zone, and the conditions were unfavorable for APB growth. In the studied lakes, heterotrophic aerobic bacteria played the main role in the aerobic oxidation of sulfur compounds in the chemocline zone. [ABSTRACT FROM AUTHOR]

The phenomenon of photosynthetic adaptation of cyanobacteria to far-red light (FRL; 700−750 nm) is closely related to such basic themes as: phototrophy, microbial ecology, and diversity of bacteria. In applied terms, this bioenergetic strategy is essential for biotechnology, with a perspective to possess additional photosynthetic energy. The majority of cyanobacteria is known to use 400−700 nm light, excited state being channeled from light-harvesting complex to reaction centers of two photosystems containing chlorophyll (Chl) a showing red maxima at ~700 nm. After the isolation of first strains producing Chls d and f it became clear that cyanobacteria can also use FRL. Large amount of data has been obtained on cyanobacteria which constitutively produce Chl d as well as on those strains which produce Chl f or Chl f/Chl d during FRL photoacclimation (FaRLiP). Inclusion of these pigments in photosynthetic apparatus, particularly using FaRLiP mechanisms, augments the adaptive potential of cyanobacteria and expands their distribution range. The review provides evidence on such aspects as: photosynthetic apparatus containing Chl d or Chld/Chl f; the FaRLiP gene cluster; phylogeny of cyanobacteria which constitutively or inducibly produce red-shifted chlorophylls; the use of chlorophylls in chemotaxonomy of cyanobacteria, and application of this character in nomenclature. [ABSTRACT FROM AUTHOR]

The composition of microbial communities and the rates of microbial processes in the water column of a meromictic trough in the Biofilter Bay, Kandalaksha Bay, White Sea were investigated in September 2020 and March 2021. The chemocline zone was located at the depths from 8 to 9 m. Sulfide was present in the monimolimnion, its concentration at the bottom reaching 25‒38 mg L–1 (0.7‒1.1 mmol). Conditions of the redox zone favored development of both anaerobic anoxygenic phototrophs and aerobic sulfur-oxidizing chemoautotrophs. A pinkish-brown bacterial plate was formed in this zone. Sequencing of the 16S rRNA gene fragments revealed predominance of green sulfur bacteria (GSB) Chlorobium phaeovibrioides. Aerobic sulfur-oxidizing bacteria Sulfurimonas sp. were the second most abundant group. Plating of chemocline samples on selective media resulted in massive formation of brown-colored Chlorobi colonies, while green GSB colonies were few. Both morphotypes were identified as Chlorobium phaeovibrioides. At the time of our study, purple sulfur bacteria (PSB) did not form a bacterial plate in the redox zone, although few PSB colonies were revealed. The PSB isolate was identified as Thiocapsa rosea. Members of this species are able to switch from photosynthesis to aerobic chemosynthesis and may compete for sulfide with sulfur-oxidizing chemo-autotrophs. We suggest that due to its openness the Biofilter Bay meromictic trough may act as a source for the propagation of anoxygenic phototrophic bacteria in the Kandalaksha Bay. [ABSTRACT FROM AUTHOR]

The interaction of singlet oxygen with bacteriochlorophyll (BChl) in the membranes, LH2 light-harvesting complexes and pigment extracts from Allochromatium (Alc.) vinosum strain MSU (previously Alc. minutissimum) was studied. The ability of carotenoids illuminated with light within their absorption region to generate singlet oxygen, which oxidizes BChl, was confirmed; BChl itself was not active in this process and acted a target for singlet oxygen. A sharp decrease in the amount of oxidized BChl in the LH2 complex under illumination in the carotenoid region was noted only at the carotenoid/complex ratio of about 0.1, i.e., when there is less than 1 carotenoid molecule per 10 LH2 complexes. It is assumed that carotenoids from the early stages of biosynthesis (neurosporene, ζ-carotene) are more active in the generation of singlet oxygen under illumination than more mature carotenoids. BChl photooxidation in LH2 complexes occurred only in the presence of oxygen. A decrease in oxygen concentration by 7 or more times resulted in a slowdown of the process or its complete stop. In model systems (pigment extract of the LH2 complex retaining the BChl/carotenoids ratio), BChl under illumination becomes both the main generator of singlet oxygen and a target for the action of the latter. Under these conditions, carotenoids do not protect BChl from oxidation. The ability of BChl850 in the LH2 complex to be oxidized by singlet oxygen suggests that it can be used as a natural sensor for this agent. [ABSTRACT FROM AUTHOR]

Bacterial diversity in attached communities of the anoxic part of the Solodovka wetland (Samara region, Russia), which feeds on cold karst springs with a high (>3 mM) sulfide content was studied using high-throughput sequencing of the variable regions V3−V4 of 16S rRNA gene. The sequences were grouped into 370 operational taxonomic units (OTUs); the OTU number per sample varied within a broad range, from 52 to 277. Taxonomic diversity in the samples depended on mat type, temperature, and sulfide concentration. The highest diversity was found in typical soft cyanobacterial mats; bacterial diversity in hard microbialites was much lower. Phototrophic bacteria formed the basis of all studied communities. In the typical mats, cyanobacteria prevailed, accompanied by phototrophic Chloroflexales, the latter being responsible for 7−13% of the total number of sequences. Hard microbialites and the mat developing at the highest sulfide concentration were characterized by low representation of these taxa and a high proportion of phototrophic Proteobacteria and Chlorobiaceae. Organisms of the sulfur cycle, Desulfobacterota and Campylobacterota, predominated in the chemotrophic part of the communities. While the organisms with fermentative metabolism and facultative chemolithotrophs were represented by a large number of OTUs, they were minor in abundance, and the sequences of the phyla Actinobacteria and Acidobacteria, which are usually widespread in oxic aquatic ecosystems have not been found. In general, the chemotrophic part of the studied communities strongly resembled the attached communities from cave streams and communities of various underground aquifers. Their phototrophic component was formed relatively independently of the chemotrophic one with the participation of the surrounding surface microbiota. The sequences most similar to some of the most abundant OTUs in the Solodovka wetland originated from the chemocline of stratified lakes, including meromictic ones. [ABSTRACT FROM AUTHOR]

The review considers the role of purple sulfur bacteria in the global cycles of hydrogen and sulfur, as well as the ecology and physiology of these bacteria in relation to the metabolism of sulfur and hydrogen. Information is presented on five types of hydrogenases involved in consumption or production of hydrogen, as well as on various enzymes involved in the oxidation/reduction of sulfur compounds. Advances in the biochemistry and genetics of the enzymes from these microorganisms make it possible to analyze the interconnection of processes at a new level. [ABSTRACT FROM AUTHOR]

The possible nitrogen sources for Osc. trichoides DG6, a typical strain of the Oscillochloridaceae family, are ammonium, N2, glutamate, asparagine, glycine, and glutamine. The assimilation of molecular nitrogen occurs with the participation of nitrogenase, the structural gene of which, nifH, is located in the gene cluster which also includes the genes of the nifD and nifK nitrogenase subunits and the auxiliary nifB gene. Considering that nifHBDK clusters have been also annotated in the genomes of other members of the Oscillochloridaceae family, including uncultured and candidate taxa, it can be assumed that the ability to fix nitrogen is a property immanent for this entire family. The pathways for assimilating ammonium in the cells grown using different nitrogen sources may differ. Osc. trichoides DG6 growing in a medium containing ammonium assimilated it with the participation of glutamate dehydrogenase, which is determined by a single gene. The expression product of this gene has dual functionality and can be used to implement the reaction with both NAD and NADP. With the growth of Osc. trichoides DG6 on a medium with glutamate as the only nitrogen source all the enzymes necessary for the implementation of the GS‑GOGAT pathway were found in the cells. However, for the glutamine synthetase reaction, ammonium, which was absent in the growth medium, was required. The source of ammonium may be glutamate metabolized through glutamate dehydrogenase. [ABSTRACT FROM AUTHOR]

Soda lakes are relic ecosystems inhabited by unique microorganisms, which are doubly extremophilic: both haloalkaliphilic and natronophilic. Two morphologically and physiologically similar monocultures of filamentous anoxygenic phototrophic bacteria (FAPB) were isolated from the water samples and biofilms on plants of the coastal zones of the steppe soda lakes Tanatar 6 and Gorchina 1 (Kulunda, Altai krai) during the season of their desalination. In their natural environments, FAPB coexisted with anoxygenic purple sulfur bacteria of the genera Chromatium,Thiocapsa, Ectothiorhodospira, and Thiorhodospira, as well as with oxygenic phototrophs (alkaliphilic cyanobacteria, euglenophytes, and diatoms). FAPB formed filaments surrounded by thin sheaths; their cells contained antenna structures (chlorosomes). Apart from small amounts of bacteriochlorophyll (BChl) a in the reaction center, both isolates contained also antenna BChl c and BChl d. Alpha- and beta-carotenes and their derivatives were also detected. FAPB grew well in the medium containing Na2S ∙ 9H2O (500 mg/L) at total mineralization of 15−30 g/L and pH 8−9.5. Identification of both cultures based on amino acid composition of the PufLM complex revealed that they belonged to the phylum Chloroflexi and were almost 100% identical both to each other and to the halo-alkaliphilic isolate "Candidatus Viridilinea mediisalina" Kir15-3F revealed previously in the Kiran soda lake (Eastern Siberia, Russia). It may be concluded that "Cand. Viridilinea mediisalina" is a typical component of Siberian soda lakes with moderate salinity. [ABSTRACT FROM AUTHOR]

The genes encoding carbonic anhydrase (CA) were found in all anoxygenic purple bacteria. The genes of α- and β-CA were found in purple nonsulfur bacteria of the class Alphaproteobacteria:Rhodospirillum rubrum, Rhodospirillum fulvum, Rhodoblastus acidophilus, and Rhodopseudomonas palustris. The alphaproteobacteria Rhodomicrobium vannielii, Blastochlorisviridis, Rhodobacter sphaeroides, Rhodobacter capsulatus, Rhodobacter veldkampii, Rhodovulumeuryhalinum, and Rhodovulum sulfidophilum possessed only the β-CA genes. Both nonsulfur purple bacteria of the class Betaproteobacteria (Rubrivivax gelatinosus) and purple sulfur bacteria (class Gammaproteobacteria) contained the α- and β-CA. No CA genes were found in green sulfur bacteria Chlorobaculum limnaeum and Chlorobaculum parvum, as well as in filamentous green nonsulfur bacteria Chloroflexus aurantiacus. However, the β-CA gene was revealed in Oscillochloris trichoides, which belonged to the latter taxonomic group. No γ-CA genes were detected in the genomes of the phototrophic bacteria studied in the present work. Although CA genes were present in all purple bacteria, the α- and β-CA activity was observed only in four species of purple nonsulfur Alphaproteobacteria: Rhodospirillum rubrum, Rhodopseudomonas palustris, Rhodoblastusacidophilus, and Rhodospirillum fulvum. These bacteria are able to synthesize CA under both photoautotrophic and photoheterotrophic conditions in the media with acetate, malate, or fructose. These bacteria (except for Rhodospirillum fulvum, which is unable to grow under aerobic conditions), also exhibit CA activity when grown under aerobic conditions in the dark. [ABSTRACT FROM AUTHOR]

The possibility of singlet oxygen generation in five species of photosynthetic bacteria under irradiation with light was studied using the Singlet Oxygen Sensor Green (SOSG) dye that, when singlet oxygen is bound, is transformed into a fluorescent endoperoxide form. Irradiation was carried out using light of different spectral composition: red (absorption of bacteriochlorophyll, BChl) and white (absorption of BChl and carotenoids). No singlet oxygen generation was detected under red light irradiation, which indicated that BChl was not involved in this process. Under white light, as the irradiation time increased, an increase in SOSG fluorescence was recorded in the membranes of four bacterial species: Allochromatium vinosum MSU, Rhodobacter sphaeroides G1C, Rba. blasticus K-1 and Rhodopseudomonas faecalis. In Rba. sphaeroides, no increase in SOSG fluorescence was observed. It is assumed that in the white light this process occurs due to the pigments that absorb in the blue-green region of the spectrum, i.e. carotenoids with 8‒11 conjugated double bonds (neurosporene, spheroidene, lycopene, and rhodopin). Similar to Trolox, SOSG may slow down the bleaching process of BChl850 in the membranes of Alc. vinosum strain MSU and may therefore effectively perform the role of a singlet oxygen trap. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) release by anoxygenic phototrophic bacteria belonging to diverse taxonomic groups is a ubiquitous process, resulting in 5–20% of the CO2 fixed by photosynthesis leaving the cell. The green photosynthetic bacterium Chlorobaculum limnaeum releases ~10% of the carbon assimilated during autotrophic СО2 fixation. Extracellular DOM release by Cba. limnaeum is a normal function of living cells, since it does not occur in the dark and is inhibited by fluoroacetate, an inhibitor of СО2 fixation via the reducing TCA acids cycle, which is used for CO2 assimilation in this bacterium. In the presence of acetate or pyruvate in the medium, DOM release increases to 30 and 60%, respectively. Nitrogen limitation stimulates DOM release by Cba. limnaeum up to 60% of assimilated СО2. Under these conditions, addition of acetate results in DOM release increasing up to 100%. Therefore, the extracellular release of DOC by anoxygenic phototrophic bacteria can be considered as an important source of substrates for the growth of heterotrophic bacteria in oxygen-free aquatic ecosystems. [ABSTRACT FROM AUTHOR]

In the present work, separation and quantitative assessment of bacteriochlorophylls d and e of green sulfur bacteria (GSB) in lake water was attempted. The method developed reveals the ratio of green- and brown-colored GSB in natural water by measurement of absorption spectra of the pigments in the extracts from environmental samples. [ABSTRACT FROM AUTHOR]

Conditions of formation and phylogenetic composition were studied for pigmented biofilms and microbial mats of the Kandalaksha Bay (White Sea) supralittoral and of the littoral of the lakes separated from the sea. During the sampling period, salinity was 15 to 26 g/L, except for several desalinated salt marsh sites (4‒11 g/L); the temperature was 9‒12°C. The species composition and structure of benthic phototrophic communities were affected by severe climatic conditions of the area, including low average annual temperature and freezing of the littoral zones. Application of Next-generation sequencing of the 16S rRNA gene V3-V4 regions combined with microscopy of the samples and obtained cultures for analysis of the biodiversity of microbial communities resulted in improved understanding of diversity of both oxygenic and anoxygenic bacteria in the Kandalaksha Bay littoral. No significant differences were revealed in species composition of microbial mats from salt marshes and shallow sites of the lakes of marine origin. Members of the phyla Bacteroidetes (up to 36%) and Proteobacteria (up to 67%) predominated in the mats and biofilms. The share of phototrophic bacteria was 0.3–18%. Oxygenic phototrophs (cyanobacteria Phormidium, Oscillatoria, Spirulina, and Anabaena, as well as diatoms) predominated in the phototrophic community. The species number of anoxygenic phototrophic bacteria did not exceed 5% of all prokaryotes. These were mainly mesophilic marine species of purple sulfur bacteria of the genera Thiorhodococcus and Thiocapsa. No members of the family Ectothiorhodospiraceae, which are typical of microbial mats from southern seas, were found in subpolar microbial mats. Nonsulfur purple bacteria and aerobic anoxygenic phototrophic bacteria were mostly similar to the known marine species. Green sulfur bacteria (salt-water Prosthecochloris and Сhlorobium species) were detected in two coastal mat samples from meromictic lakes. Anoxygenic filamentous phototrophic bacteria, which occurred in almost all benthic phototrophic communities, were represented by new phylotypes. [ABSTRACT FROM AUTHOR]

Phototrophic communities forming in the bottom of the Berikei highly mineralized mesothermal sulfide springs (Kayakent region, Dagestan, Russia) were investigated. The Berikei springs are an interesting example of combined effect of such factors as temperature, salinity, pH, and sulfide of occurrence and structure of phototrophic microbial communities. The water was of the sodium chloride type with salinity of 48‒97 g/L, near-neutral brine pH, and sulfide concentration of ~1 mM. The temperature at the stream bottom was as high as 60°C. Elevated temperature and high salinity limited the development of phototrophic communities. Formation of cyanobacterial mats occurred at temperatures below 54°C. Phormidium-like cyanobacteria and unicellular Synechocystis sp. predominated in the mats. The number of cyanobacterial species increased at desalination to 48‒57 g/L with emergence of the species morphologically resembling Spirulina sp., Leptolyngbya sp., and Oscillatoria sp. Among anoxygenic phototrophic bacteria, halophilic purple bacteria Ectothiorhodospira sp., Marichromatium sp., and Rhodovulum sp., green sulfur bacteria Prosthecochloris sp., and unidentified Chloroflexi were present. Oxygenic photosynthesis in the mats was not inhibited by sulfide. Production of cyanobacterial mats was up to 4.7‒53.8 µg/(cm2 h). The contribution of anoxygenic phototrophic bacteria to photosynthetic production varied from 0 to 100%. The composition of this microbial community was compared to those of the phototrophic microbial communities of the mesothermal springs of the Dead Sea coast (Israel), the Washington warm lake (United States), and the Paoha Island hot springs (Mono Lake, United States. [ABSTRACT FROM AUTHOR]

The community of anoxygenic phototrophic bacteria (APB) from the water column of the meromictic Lake Trekhtsvetnoe (Kandalaksha Bay, White Sea, Russia) was studied in March 2012 and 2013 and in September 2013 and 2014. The community structure below the chemocline was shown to restore during three years after partial mixing resulting from seawater admixture into the lake in autumn 2011; a dense layer (at least 108 cells mL–1) of green-colored (g/c) sulfur bacteria (GSB) was formed. During winter, development of low numbers of brown colored (b/c) GSB was observed in the upper layer of green water. During summer seasons, b/c GSB were found to be located in the oxic zone above the green water layer, which was unusual for these organisms. The APB community was found to contain purple bacteria. Four APB strains were isolated from the upper part of the sulfide zone. The b/c and g/c GSB strains were phylogenetically close to each other and to the type species Chlorobium phaeovibrioides DSM 265 (99% similarity gene sequences). One strain of purple bacteria was phylogenetically related to the brackish sulfur bacteria Thiocapsa marina, while the other was related to freshwater bacteria Rhodopseudomonas palustris. The strains of sulfur bacteria were phylogenetically close to the chemocline bacteria from the stratified Lake Kislo-Sladkoe, also located in the coastal zone of the Kandalaksha Bay, White Sea. [ABSTRACT FROM AUTHOR]

The effect of singlet oxygen was studied in the system of Allochromatium (Alc.) vinosum MSU membranes, rose bengal, and light (547−600nm) with and without a quencher. In the system without a quencher, bleaching of the BChl850 band of the LH2 light-harvesting complex was observed and an absorption peak emerged at 698 nm, which belonged to the oxidized product, 3-acetyl-chlorophyll. The efficiency of five quenchers of singlet oxygen for neutralization of the effect of singlet oxygen on bacteriochlorophyll in the light-harvesting complexes of the membranes Alc. vinosum MSU was studied: sodium ascorbate, histidine, imidazole, trolox, and sodium azide. All of them, with the exception of sodium azide, neutralized successively the effect of singlet oxygen. [ABSTRACT FROM AUTHOR]

The R and M phase variants of Rhodobacter sphaeroides and Rhodobacter capsulatus were isolated. The growth rates in the dark and in the light in glucose-containing media were much higher for the Rba. sphaeroides R variant than for the M variant. For the Rba. capsulatus R and M variants, growth rates in the dark and in the light in fructose- or glucose-containing media differed insignificantly. The cells of Rba. sphaeroides and Rba. capsulatus phase variants growing in media with glucose and fructose exhibited differences in activity of the key enzymes of the Embden-Meyerhof-Parnas (EMP) and Entner-Doudoroff (ED) pathways. The oxidative pentose phosphate pathway (PPP) does not participate in glucose and fructose metabolism in the studied bacteria. Specific activity of the ED pathway enzymes was higher in dark-grown R and M variants of both Rba. sphaeroides and Rba. capsulatus than in the cells grown under light. Specific activity of the EMP enzymes was higher for the R and M variants of both cultures grown in the light than for those grown in the dark. Activities of the 2-keto-3-deoxy-6-phosphogluconate and fructose bisphosphate aldolases, the key enzymes of the ED and EMP pathways in Rba. sphaeroides M variant grown in the medium with glucose in the light or in the dark, were approximately twice those of the R variant. In the medium with fructose activities of these enzymes in both R and M variants did not change significantly depending on growth conditions. Activities of the enzymes of the EMP and ED pathways in the extracts of the Rba. capsulatus R and M cells grown with glucose or fructose did not change significantly. Cultivation of Rba. sphaeroides and Rba. capsulatus phase variants in the medium with fructose resulted in a considerably increased synthesis of 1-phosphofructokinase. Induction of 1-phosphofructokinase synthesis in Rba. sphaeroides occurred only in the light, while in Rba. capsulatus induction of this enzyme in the medium with fructose was observed both in the dark and in the light. Thus, under aerobic conditions in the dark the phase variants of both bacteria probably assimilated glucose and fructose via the ED pathway, while in the light the EMP pathway was active. [ABSTRACT FROM AUTHOR]

A strain of aerobic anoxygenic phototrophic bacteria (AAPB) isolated from the surface of a cyanobacterial mat of an Eastern Siberian thermal spring (40°C) and designated Se-4 was identified as Porphyrobacter donghaensis according to its 16S rRNA gene sequence. A DNA-DNA hybridization level of 95% was determined between strain Se-4 and the type strain of this species, SW-132. The isolate was an obligate aerobe, forming orange round colonies on solid media, which turn red in the course of growth. The cells were motile rods capable of branching. The cells divided by uniform fission by constriction. Optimal growth was observed at pH 7.5 and NaCl concentrations from 0 to 1 g/L. The pigments present were carotenoids and bacteriochlorophyll a. Another Porphyrobacter donghaensis strain, Noj-1, isolated from a purple mat developing on the surface of a coastal set-up in a steppe weakly mineralized (1.5 g/L) soda lake Nozhii (Eastern Siberia) possessed similar characteristics. Thus, the AAPB species Porphyrobacter donghaensis was shown to occur, apart from marine environments (its known habitat), also in weakly mineralized soda lakes and freshwater thermal springs. Description of the species Porphyrobacter donghaensis was amended. [ABSTRACT FROM AUTHOR]

Size exclusion chromatography was used to assess the relative size of intact and diphenylamine-treated (DPA, with suppressed carotenoid synthesis) peripheral light-harvesting complexes (LH2 complexes) of the sulfur bacterium Allochromatium minutissimum. Both LH2 complexes were nonamers and had the same elution volume V, coinciding with that for the LH2 complex of Rhodoblastus acidophilus (strain 10050). Their molecular weight was 150 kDa. Both pheophytinization of bacteriochlorophyll (BChl) at low pH and treatment with the detergent LDAO, which affects the hydrophobic interactions between the neighboring protomers, result in the fragmentation of the ring of the isolated LH2 complexes and formation of 55-kDa fragments with molecular weights corresponding to one-third of the initial value. Fragmentation caused by both pheophytinization and detergent treatment was much more rapid in DPA LH2 complexes than in the intact ones. The 55-kDa fragments formed at low pH values contained monomeric bacteriopheophytin, while the fragments of a similar molecular weight formed at pH 8.0 in the presence of the detergent contained monomeric BChl. The observed fragmentation was hypothesized to reflect the inherent C symmetry of the LH2 complexes, with the preliminarily assembled trimers used as building blocks. [ABSTRACT FROM AUTHOR]

The R and M variants of a purple photosynthetic bacterium Rhodobacter sphaeroides 2R grown on a medium with acetate accumulate poly-ß-hydroxybutyrate (PHB). Accumulation of this polymer occurs in the cells grown either anaerobically on the light or aerobically in the dark. On the medium with C/N imbalance (C/N = 4), PHB content during the stationary growth phase under aerobic conditions in the dark was 40 and 70% of the dry biomass of the R and M variant, respectively. The Rba. sphaeroides M variant is therefore a promising culture for large-scale PHB production. Investigation of activity of the TCA cycle enzymes revealed that decreased activity of citrate synthase, the key enzyme for acetate involvement in the reactions of the tricarboxylic acid cycle, was primarily responsible for enhanced PHB synthesis by Rba. sphaeroides. Moreover, the Rba. sphaeroides M variant grown under aerobic conditions in the dark exhibited considerably lower activity of NADH oxidase, which participates in the oxidation of reduced NADH produced in the TCA cycle during acetate oxidation. The combination of these two factors increases the possibilities for acetate assimilation via an alternative mechanism of PHB synthesis. [ABSTRACT FROM AUTHOR]

According to paleontological data, large-scale, global glaciations occurred repeatedly over the history of Earth. Such glaciations unavoidably resulted in a sharp decrease in the number of habitats suitable for development of phototrophic microorganisms, which mostly require sunlight. Molecular data indicate that some groups of Antarctic phototrophic microorganisms emerged before formation of the Antarctic ice sheet (30-45 Ma) and probably survived the subsequent glaciation maxima. Analysis of the data on the present-day occurrence of phototrophs in Antarctica revealed the presence of liquid water in a habitat to be the key factor for survival of phototrophic communities. At negative air temperatures, this requirement may be met either in warmer microniches (0 to 30°C and higher) or in brines with freezing temperatures below zero (to −52°C). Development of phototrophic communities in such habitats may indicate the theoretical possibility of existence of the niches favoring growth of phototrophic microorganisms during Precambrian global glaciations. This possibility should be considered in paleontological reconstructions of development of life on Earth. [ABSTRACT FROM AUTHOR]

Cyanobacteria are a group of oxygenic phototrophs that have existed for at least 3.5 Ga. Photosynthetic CO assimilation by cyanobacteria occurs via the Calvin cycle, with RuBisCO, its key enzyme, having very low affinity to CO. This is due to the fact that atmospheric CO concentration in Archaean, when the photosynthetic apparatus evolved, was several orders higher than now. Later, in the epoch of Precambrian microbial communities, CO content in the atmosphere decreased drastically. Thus, present-day phototrophs, including cyanobacteria, require adaptive mechanisms for efficient photosynthesis. In cyanobacterial cells, this function is performed by the CO-concentrating mechanism (CCM), which creates elevated CO concentrations in the vicinity of RuBisCO active centers, thus significantly increasing the rate of CO fixation in the Calvin cycle. CCM has been previously studied only for freshwater and marine cyanobacteria. We were the first to investigate CCM in haloalkaliphilic cyanobacteria from soda lakes. Extremophilic haloalkaliphilic cyanobacteria were shown to possess a well-developed CCM with the structure and functional principles similar to those of freshwater and marine strains. Analysis of available data suggests that regulation of the amount of inorganic carbon transported into the cell is probably the general CCM function under these conditions. [ABSTRACT FROM AUTHOR]

Purple bacteria are able to use H for photoautotrophic, photomixotrophic, and chemoautotrophic growth, exhibiting high metabolic lability. Depending on the type of metabolism, hydrogen may be consumed with release of energy and/or reductive equivalents. Purple bacteria may also release H as a terminal electron acceptor or in the course of dinitrogen fixation. Thus, hydrogen metabolism in purple bacteria is diverse; these bacteria are often used as models for investigation of the metabolic traits and interrelation of the metabolic pathways involving molecular hydrogen. In this review, the present-day state of investigation of hydrogen metabolism in purple bacteria is reflected and its possible practical applications are discussed. Nitrogenase and hydrogenase, the major key enzymes of hydrogen metabolism, are discussed in brief. A generalized scheme of H role in the metabolism of purple bacteria is presented. Experimental approaches for investigation of the rates of hydrogen production are discussed. Immobilized systems are noted as the most promising approach for development of model systems for hydrogen production. [ABSTRACT FROM AUTHOR]

Five phylogenetically similar monocultures of mesophilic filamentous anoxygenic phototrophic bacteria (FAPB) were isolated from microbial mats of low-mineral (5-28 g/L) alkaline lakes in Buryat Republic, Transbaikalia and Mongolia, as well as from biofilms of an alkaline sulfide spring (3 g/L) of the Umhei hydrothermal system (Buryat Republic). New isolates were characterized by short trichomes (15-30 μm long and ∼1 μm in diameter), straight, curved, or wavy, surrounded by a thin iron-sorbing mucous sheath. Gliding motion of the trichomes was not observed. The trichomes formed bunches consisting of several filaments. Trichomes multiply by the separation of short fragments or single cells from the parental trichome. The cells in the filaments were elongated; they contained chlorosomes, gas vesicles, poly-β-hydroxybutyrate granules, and small polyphosphate inclusions. Bacteria contained bacteriochlorophylls c and a and γ-carotene. Absorption maxima of the pigments in the cells were observed at 462, (shoulder at 515), 742, 805, and 863 nm. The organisms were strict anaerobes capable of photoautotrophic growth with sulfide as an electron donor. Elemental sulfur emerged into the medium as a result of sulfide photooxidation. The organisms were tolerant to sulfide (up to 8 mM). Best growth occurred at pH 8.0, 3-15 g/L NaCl, and 1-5 g/L sodium bicarbonate. According to phylogenetic analysis, the 16S rRNA gene sequences of the FAPB isolates formed a separate cluster most closely related to the species cluster of the family Oscillochloridaceae, suborder Chloroflexinae, order Chloroflexales, class Chloroflexi. The differences with the closest 16S rRNA gene sequences of the known FAPB were 9-10%. The formal description of a new taxon, Candidatus' Chloroploca asiatica' gen. nov., sp. nov., is provided. [ABSTRACT FROM AUTHOR]

The composition and macroscopic structure of the floating oxygenic phototrophic communities from Kulunda steppe soda lakes (Cock Soda Lake, Tanatar VI, and Bitter Lake 3) was described based on the data of the 2011 and 2012 expeditions (Winogradsky Institute of Microbiology). The algo-bacterial community with a green alga Ctenocladus circinnatus as an edificator was the typical one. Filamentous Geitlerinema sp. and Nodosilinea sp. were the dominant cyanobacteria. Apart from C. circinnatus, the algological component of the community contained unicellular green algae Dunaliella viridis and cf. Chlorella minutissima, as well as diatoms ( Anomoeoneis sphaerophora, Brachysira brebissonii, Brachysira zellensis, Mastogloia pusilla var. subcapitata, Nitzschia amphibia, Nitzschia communis, and Nitzschia sp.1). The latter have not been previously identified in the lakes under study. In all lakes, a considerable increase in salinity was found to result in changes in the composition and macroscopic structure of algo-bacterial communities. [ABSTRACT FROM AUTHOR]

Growth, bacteriochlorophyll a content, electron transport chain (ETC), and activities of the tricarboxylic acid (TCA) cycle enzymes were studied in R and M phase variants of Rhodobacter sphaeroides cells grown anaerobically in the light and aerobically in the dark. Under all cultivation conditions tested, bacteriochlorophyll a content was 2-3 times lower in the cells of the M variant compared to the R variant, which therefore was predominant in the cultures grown in the light. In both variants, activity of all TCA cycle enzymes was higher for the cells grown in the dark under aerobic conditions. When grown aerobically in the dark, the R variant, unlike the M variant, did not contain cytochrome aa, acting as cytochrome c oxidase, in its ETC. An additional point of coupling the electron transfer to the generation of the proton gradient at the cytochrome aa level provided for more efficient oxidation of organic substrates, resulting in predominance of the M variant in the cultures grown in the dark under aerobic conditions. [ABSTRACT FROM AUTHOR]

A bacterial strain De was isolated from the surface water layer of the meromictic soda lake Doroninskoe. When grown in the dark, it formed pink colonies on agar media. The cells were nonmotile, containing bacteriochlorophyll a and carotenoids. Stationary-phase cells contained intracellular vesicular membranes similar to the membranes of the photosynthetic apparatus of some nonsulfur purple bacteria. Aerobic growth did not occur. Sucrose, citrate, mannitol, sorbitol, casein hydrolysate, and yeast extract were the preferable substrates for aerobic growth. Xylose, lactose, aspartate, benzoate, malate, malonate, succinate, tartrate, formate, fumarate, glycerol, methanol, and ethanol were not utilized. Growth occurred at up to 50 g/L NaCl (optimum at 5 g/L) and pH 9.8. According to the 16S rRNA gene sequencing, similarity between the isolate and the known alkaliphilic genera of nonsulfur purple bacteria ( Rhodobaca) and of aerobic anoxygenic phototrophic bacteria ( Roseinatronobacter) was 96%, which was sufficient for the description of a new genus of aerobic anoxygenic phototrophic bacteria. The name Roseibacula alcaliphilum gen. nov., sp. nov. was proposed for the isolate. [ABSTRACT FROM AUTHOR]

Species composition of anoxygenic phototrophic bacteria in microbial mats of the Goryachinsk thermal spring was investigated along the temperature gradient. The spring belonging to nitrogenous alkaline hydrotherms is located at the shore of Lake Baikal 188 km north-east from Ulan-Ude. The water is of the sulfate-sodium type, contains trace amounts of sulfide, and salinity does not exceed 0.64 g/L, pH 9.5. The temperature at the outlet of the spring may reach 54°C. The cultures of filamentous anoxygenic phototrophic bacteria, nonsulfur and sulfur purple bacteria, and aerobic anoxygenic phototrophic bacteria were identified using the pufLM molecular marker. The fmoA marker was used for identification of green sulfur bacteria. Filamentous cyanobacteria predominated in the mats, with anoxygenic phototrophs comprising a minor component of the phototrophic communities. Thermophilic bacteria Chloroflexus aurantiacus were detected in the samples from both the thermophilic and mesophilic mats. Cultures of nonsulfur purple bacteria similar to Blastochloris sulfoviridis and Rhodomicrobium vannielii were isolated from the mats developed at high (50.6-49.4°C) and low temperatures (45-20°C). Purple sulfur bacteria Allochromatium sp. and Thiocapsa sp., as well as green sulfur bacteria Chlorobium sp., were revealed in low-temperature mats. Truly thermophilic purple and green sulfur bacteria were not found in the spring. Anoxygenic phototrophic bacteria found in the spring were typical of the sulfur communities, for which the sulfur cycle is mandatory. The presence of aerobic bacteriochlorophyll a-containing bacteria identified as Agrobacterium ( Rhizobium) tumifaciens in the mesophilic (20°C) mat is of interest. [ABSTRACT FROM AUTHOR]

The community of anoxygenic phototrophic bacteria (APB) in the water column of the Kislo-Sladkoe stratified lake recently isolated from the sea (White Sea, Kandalaksha Bay) was investigated in September 2010. The water of the sulfide-rich zone was greenish-brown due to intense development of green sulfur bacteria (GSB). Nine APB strains were isolated from the water samples: three belonging to GSB, five, to purple sulfur bacteria (PSB), and one, to purple nonsulfur bacteria (PNB). GSB predominated in the phototrophic community of the chemocline. Unexpectedly, two morphologically different green-colored GSB strains were found to be phylogenetically identical and related to the brown-colored Chlorobium phaeovibrioides (99% similarity according to the 16S rRNA gene sequencing). Homology to the closest green-colored species ( Chlorobium luteolum) was 98%. Two morphologically and physiologically similar PSB strains ( TcrPS10 and AmPS10) had rounded cells containing okenone and gas vesicles. According to the 16S rRNA gene sequencing, these strains were most closely related (99%) to two different Thiocapsa species: Tca. marina (containing okenonee and no gas vesicles) and Tca. rosea (containing spirilloxanthin and gas vesicles). The remaining isolates of purple bacteria were similar to the already described APB species. [ABSTRACT FROM AUTHOR]

Pheophytinization of bacteriochlorophyll (BChl) at low pH was investigated in the core (LH1) and peripheral (LH2) light-harvesting complexes, as well as in the ensemble of the reaction center (RC) with the LH1 complex. The stages in disintegration of the native BChl forms in the LH1 complex and in its ensemble with RC were revealed. They were observed as emergence of the absorption band of monomeric BChl and an increase in its intensity, followed by its transformation into the band of monomeric bacteriopheophytin (BPh) and then into the band of aggregated BPh. Unlike the LH1 complex, in the case of the LH2 complex, monomeric BChl was never detected as an intermediate product. While the spectra revealed formation of monomeric BPh, its accumulation did not occur, since its aggregation is very rapid compared to that in the LH1 complex and in the RC-LH1 ensemble. PAAG electrophoresis revealed that pheophytinization of BChl in the LH2 complex was accompanied by disruption of the stable cylindrical structure of this complex with emergence of characteristic fragments consisting of α and β peptides and bearing monomeric BPh, as well as of the α peptide aggregates bearing BPh aggregates. Unlike the LH2 complex, BChl pheophytinization in the LH1 complex did not result in its fragmentation. This is an indication of different types of structural stabilization in the LH1 and LH2 complexes. In the LH2 complex, coordination of bacteriochlorophyll Mg by conservative histidine residues of the α and β polypeptides is the main factor responsible for the maintenance of its cylindrical structure. Stability of the LH1 complex is probably based primarily on the highly specific hydrophobic interactions between the surfaces of individual polypeptide chains, since the presence of hydrogen bonds results in autonomy of each αβBChl subunit, rather than in stabilization of the LH1 complex as a whole. [ABSTRACT FROM AUTHOR]

The interaction between freshwater nonsulfur purple bacteria Rhodopseudomonas sp. UZ-25p (Uzon caldera, Kamchatka, Russia) and two kaolinite samples (Zhuravlinyi Log, Chelyabinsk oblast) was investigated. Alterations in the chemical composition of the minerals and solutions, the parameters of bacterial growth, and crystal morphology and mineralogy of the kaolinite samples indicated the interactions between all components of the system (minerals, water, growth medium, and bacteria). Bacteria removed some elements from the medium, used them for growth, and promoted their transition into the mineral exchange pool. In the presence of bacteria, kaolinite cation exchange capacity increased and saturation of kaolinites with bases occured. Partial biodegradation of kaolinites, accompanied by ordering of the crystalline structure of their lamellar phase, was the main factor responsible for the increase in cation exchange capacity. For the first time anoxygenic phototrophic bacteria were found to degrade kaolinite with formation of gibbsite. The theoretical and applied significance of the experimental results is discussed. [ABSTRACT FROM AUTHOR]

The ability of purple photosynthetic bacteria to form phase variants (dissociants) was discovered. The R and M phase variants were isolated from the Rhodobacter sphaeroides population, and their affiliation with the parent strain was confirmed by the PCR of their 16S rRNA gene fragments. The R and M variants were different both in colony morphology and in resistance to some physical and chemical factors. The R variant of Rhb. sphaeroides had advantages when grown in the light, at elevated temperature, under aeration, and UV irradiation, whereas the M variant had advantages when grown aerobically in the dark or at increased NaCl concentrations. [ABSTRACT FROM AUTHOR]

Phototrophic sulfur bacteria form dense accumulations in the chemocline zones of stratified lakes where light reaches the sulfide-containing layers of water. Many works are dedicated to the ecophysiology of these microorganisms in meromictic lakes. However, the role of these microorganisms in the trophic network of these ecosystems, the ways of biomass utilization, and the contribution to the turnover of biogenic elements have so far been insufficiently understood. This work deals with the analysis of many years' seasonal dynamics of the biomass of purple sulfur bacteria and the physicochemical conditions of their environment in Lake Shunet (Siberia, Khakassia, Russia), unraveling the causes of their anomalous development in the chemocline of this lake, as well as the comparative analysis of such type of ecosystems. Lake Shunet is characterized by markedly pronounced stratification and the high density of purple sulfur bacteria (PSB) in the chemocline, which is comparable to that of Lake Mahoney (Canada) where the number of PSB is the greatest among those known in the world. It was shown that, in the period 2002-2009, the total amount of bacterio-chlorophyll a in the water column of Lake Shunet increased and did not correlate with the seasonal variations in temperature and illumination in the chemocline. It was established that PSB cells in the purple layer experienced the effect of self-shading. The sedimentation rate of purple sulfur bacteria in Lake Shunet was low due to the pronounced density gradient in the chemocline zone. Thus, the high number of PSB in the chemocline was due to the combination of strong illumination, a high sulfide concentration, and a high water density gradient, which was responsible for stable stratification and contributed to the accumulation of the cells in a narrow layer. The data obtained could be useful for the paleoreconstruction of climatically deter-mined changes in the level of the lake and its periods of meromixis by the presence of carotenoids and bacte-riochlorophylls in the bottom sediments. [ABSTRACT FROM AUTHOR]

External factors affecting the activity of isocitrate lyase (ICL) in Rhodobacter capsulatus B10 grown under controlled photoheterotrophic anaerobic conditions were investigated. The activity of this enzyme was found to depend on the history of the inoculum and on the growth phase on acetate medium. Intracellular degradation of ICL under unfavorable conditions was shown. However, transition of the growing culture from acetate to lactate did not result in active degradation of the enzyme. When transferred to acetate, Rba. capsulatus could grow without the lag phase and did not exhibit ICL activity, suggesting another anaplerotic pathway in Rba. capsulatus cells. Since emergence of the ICL activity in the cells grown on acetate results in an increase in its growth rate, the glyoxylate bypass plays an important role in acetate metabolism of Rba. Capsulatus. [ABSTRACT FROM AUTHOR]

The physicochemical properties, species composition, and vertical distribution of microorganisms in the water column, shoreline microbial mat, and small shoreline mud volcanoes of the stratified soda Lake Doroninskoe were investigated in September 2007. The lake is located in the Transbaikal region, in the permafrost zone (51°25′N; 112°28′E). The maximal depth of the contemporary lake is about 6 m, the pH value of the water is 9.72, and the water mineralization in the near-bottom horizon is 32.3 g l−1. In summer, the surface oxygen-containing horizon of the water column becomes demineralized to 26.5 g l−1; at a depth of 3.5–4.0 m, an abrupt transition occurs to the aerobic zone containing hydrosulfide (up to 12.56 g l−1). Hydrosulfide was also detected in trace quantities in the upper water horizons. The density stratification of the water column usually ensures stable anaerobic conditions until the freezing period (November and December). The primary production of oxygenic phototrophs reached 176–230 μg l−1. High rates of dark CO2 assimilation (61–240 μg l−1) were detected in the chemocline. Within this zone, an alkaliphilic species of sulfur-oxidizing bacteria of the genus Thioalkalivibrio was detected (104 cells ml−1). Lithoheterotrophic bacteria Halomonas spp., as well as bacteriochlorophyll a-containing aerobic anoxygenic phototrophic bacteria (AAP) Roseinatronobacter sp. capable of thiosulfate oxidation, were isolated from samples collected from the aerobic zone (0–3 m). The water transparency in September was extremely low; therefore, no visible clusters of anoxygenic phototrophic bacteria (APBs) were detected at the boundary of the hydrosulfide layer. However, purple sulfur bacteria which, according to the results of the 16S rRNA gene analysis, belong to the species Thioalkalicoccus limnaeus, Ectothiorhodospira variabilis, “Ect. magna,” and Ect. shaposhnikovii, were isolated from samples of deep silt sediments. Ect. variabilis and Ect. shaposhnikovii were the major APB species in the shoreline algo-bacterial mat. The halotolerant bacterium Ect. shaposhnikovii, purple nonsulfur bacteria of the genus Rhodobacter, and AAP of Roseococcus sp. were isolated from the samples collected from mud volcanoes. All these species are alkaliphiles, moderate halophiles, or halotolerant microorganisms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Mass-spectrometric investigation of carbon isotope composition (δ13C) was carried out for suspended organic matter and dissolved mineral compounds for the water column of some meromictic water bodies differing in salinity and trophic state. As a rule, a more pronounced carbon isotope fractionation (resulting from the metabolism of phytoplankton and anoxygenic phototrophic bacteria) was revealed in the zones of enhanced oxygenic and anoxygenic photosynthesis. Carbon isotope fractionation at the border between oxidized and reduced waters depends both on the activity of microbial communities and on the dominant species of phototrophic microorganisms. Analysis of the distribution profiles of the isotopic composition of suspended organic matter and dissolved mineral carbon revealed active mineralization of the organic matter newly formed via anoxygenic photosynthesis in the monimolimnion by microbial communities, resulting in the release of isotopically light carbon dioxide. Mineral carbon in the anaerobic zones of highly productive meromictic water bodies is therefore enriched with the light 12C isotope. [ABSTRACT FROM AUTHOR]

Variation of the distribution of bacteriochlorophyll a (BChl a) between external antenna (LH2) and core complexes (LH1 + RC) of the photosynthetic membrane of the sulfur bacterium Allochromatium minutissimum was studied at light intensities of 5 and 90 Wt/m2 in the temperature range of 12–43°C. The increase of light intensity was shown to result in a 1.5-to 2-times increase of a photosynthetic unit (PSU). PSU sizes pass through a maximum depending on growth temperature, and the increase of light intensity (5 and 90 Wt/m2) results in a shift of the maximal PSU size to higher temperatures (15 and 20°C, respectively). In the narrow temperature interval of ∼14–17°C, the ratio of light intensity to PSU size is typical of phototrophs: lower light intensity corresponds to larger PSU size. The pattern of PSU size change depending on light intensity was shown to differ at extreme growth temperatures (12°C and over 35°C). The comparison of Alc. minutissimum PSU size with the data on Rhodobacter capsulatus and Rhodopseudomonas palustris by measuring the effective optical absorption cross-section for the reaction of photoinhibition of respiration shows a two to four times greater size of light-harvesting antenna for Alc. minutissimum, which seems to correspond to the maximum possible limit for purple bacteria. [ABSTRACT FROM AUTHOR]

The anoxygenic phototrophic bacterial community of the high-altitude meromictic Lake Gek-Gel (Azerbaijan) was investigated in September 2003. The highest concentration of bacteriochlorophyll e (48 μg/l) was detected at a depth of 30 m; the peak of bacteriochlorophyll a (4.5 μg/l) occurred at 29 m. Phylogenetic analysis revealed that brown-colored green sulfur bacteria Chlorobium phaeobacteroides predominated in the lake. Nonsulfur purple bacteria phylogenetically close to Blastochloris sulfoviridis were found in insignificant amounts; these organisms have not been previously reported in Lake Gek-Gel. [ABSTRACT FROM AUTHOR]

We investigated the formation of the B800-850 complex in cells of the bacterium Rhodopseudomonas palustris AB illuminated by red and blue light under anaerobic growth conditions. Under red illumination, the B800-850 complex was assembled with a reduced absorption band at 850 nm. The results of re-electrophoresis of the B800-850 complex and oxidation in the presence of potassium iridate suggest its heterogeneity. It may be a mixture of two complexes (B800 and B800-850). The B800-850 complex lacks the capacity for conformational transitions if assembled under blue illumination. Accordingly, the light-harvesting complex assembled in the blue light contains polypeptides that are not synthesized under normal conditions or at increased or decreased light intensities. The mechanism of regulation of the synthesis of the polypeptides of light-harvesting the B800-850 complex and its dependence on the spectral composition of the light is discussed. [ABSTRACT FROM AUTHOR]

The functional roles of the malate dehydrogenase (MDH) tetrameric and dimeric isoforms in the metabolism of the purple nonsulfur phototrophic bacterium Rhodopseudomonas palustris, strain f-8pt was studied with the use of specific inhibitors. It was shown that the enzyme tetrameric form allows the functioning of the glyoxylate cycle and the dimeric form provides for the operation of the tricarboxylic acid cycle. [ABSTRACT FROM AUTHOR]

The effect of pH on the structure of the communities of anoxygenic phototrophic bacteria (APB) was studied under laboratory conditions. Samples of natural APB communities were inoculated into media that differed in pH values, which were 7, 9.5, or 10.5. The structure of the APB communities in the obtained enrichment cultures at all pH values depended also on the mineralization levels of the media, which were the same as in the lakes from which samples were taken. The same dependence of the community structure on salinity was observed as in the case of the natural communities that had been described previously. APB were most diverse in the enrichment cultures grown at pH 9.5. The shift of the pH to either neutral or extremely alkaline values restricted the species diversity within the APB community, resulting in marked predominance of the most adapted forms. It was shown that the status of Ectothiorhodospira species within the community could serve not only as an indicator of salinity but also as an indicator of pH in soda lakes with a water mineralization of higher than 5 g/l. The statuses of various APB groups in the community as dependent on pH and salinity are discussed, as well as possible changes in these statuses due to changes in the water level and other environmental parameters in the studied lakes. [ABSTRACT FROM AUTHOR]

The anoxygenic phototrophic bacterial community of the brackish meromictic Lake Shira (Khakassia) was investigated in August 2001, July 2002, and February–March 2003. In all the periods of investigation, the prevailing microorganisms were purple sulfur bacteria similar to Lamprocystis purpurea in morphology and pigment composition. Their highest number (3 × 105 cells/ml) was recorded in July 2002 at the depth of 15 m. According to 16S rRNA gene analysis, the strain of purple sulfur bacteria isolated in 2001 and designated Sh Am01 exhibited 98.6% similarity to the type strain of Thiocapsa roseopersicina and 97.1–94.4% similarity to the type strains of Tca. pendens, Tca. litoralis, and Tca. rosea. The minor microorganisms of the anoxygenic phototrophic bacterial community within the period of investigation were nonsulfur purple bacteria phylogenetically close to Rhodovulum strictum (98.3% similarity, strain Sh Rb01), Ahrensia kielensis (of 93.9% similarity, strain Sh Rb02), Rhodomicrobium vannieli (of 99.7% similarity, strain Sh Rmc01), and green sulfur bacteria, phylogenetically close to Chlorobium limicola (of 98.7% similarity, strain Sh Cl03). [ABSTRACT FROM AUTHOR]

Seasonal studies of the anoxygenic phototrophic bacterial community of the water column of the saline eutrophic meromictic Lake Shunet (Khakassia) were performed in 2002 (June) and 2003 (February–March and August). From the redox zone down, the lake water was of dark green color. Green sulfur bacteria predominated in every season. The maximum number of green sulfur bacteria was 107 cells/ml in summer and 106 cells/ml in winter. A multi-syringe stratification sampler was applied for the study of the fine vertical distribution of phototrophs in August 2003; the sampling was performed every 5 cm. A 5-cm-thick pink-colored water layer inhabited by purple sulfur bacteria was shown to be located above the layer of green bacteria. The species composition and ratio of purple bacterial species depended on the sampling depth and on the season. In summer, the number of purple sulfur bacteria in the layer of pink water was 1.6 × 108 cells/ml. Their number in winter was 3 × 105 cells/ml. In the upper oxygen-containing layer of the chemocline the cells of purple nonsulfur bacteria were detected in summer. The maximum number of nonsulfur purple bacteria, 5 × 102 cells/ml, was recorded in August 2003. According to the results of the phylogenetic analysis of pure cultures of the isolated phototrophic bacteria, which were based on 16S rDNA sequencing, green sulfur bacteria were close to Prosthecochloris vibrioformis, purple sulfur bacteria, to Thiocapsa and Halochromatium species, and purple nonsulfur bacteria, to Rhodovulum euryhalinum and Pinkicyclus mahoneyensis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The pigment and auxotrophic mutants of Rhodobacter sphaeroides Y6 were obtained by treatment with ethyl methanesulfonate (EMS) followed by lithium chloride (LiCl). Treatment with 0.081 MEMS and subsequent treatment with 0.071 M LiCl resulted in 12% higher frequency og than that by 0.081 mol/L EMS alone, and the same frequency of pigment mutations than application of 0.081 M EMS alone; the frequency of auxotrophic mutations increased 2.5-fold when treatment with lithium chloride was applied. A blue shift by 10 nm was recorded in the absorption spectrum of carotenoids form YM5-3 green mutant; considerable accumulation of neurosporine was revealed by HPLC and mass spectrometry. The method is efficient for isolating the mutants of photosynthetic bacteria. [ABSTRACT FROM AUTHOR]