Strains Of Purple Nonsulfur Bacteria Research Articles

New tolerant strains of purple nonsulfur bacteria for hydrogen production in a two-stage integrated system

In this study we described the isolation of eight new strains of purple non-sulfur bacteria resistant to salinity ≥30 g L−1 and high concentration of VFAs (200 mM). These strains were characterized by their general physiological properties and the occurrence of hupSL genes. Some correlation was observed between the rate of H2 photoproduction, the absence of hupSL genes and hydrogenase activity. Two fast-growing strains without hupSL genes showed high nitrogenase activity and hydrogen accumulation during growth on Ormerod medium. These strains were capable of H2 photoproduction using non-treated dark culture (75% in water) after dark fermentation of starch at 30 g L−1, unlike control strains, Rhodobacter capsulatus B10 and Rb. sphaeroides GL. New N7 and 13 strains identified as Rb. sphaeroides can be recommended for application in a two-stage H2 production system.

Rhodovulum tesquicola sp. nov., a haloalkaliphilic purple non-sulfur bacterium from brackish steppe soda lakes

Two strains of purple non-sulfur bacteria (A-36s(T) and A-51s) were isolated from brackish steppe soda lakes of southern Siberia. Genetically, the isolates were related most closely to the type strains of Rhodovulum steppense and Rhodovulum strictum, from which they differed at the species level (98.5% 16S rRNA gene sequence similarity, 40-53% DNA-DNA relatedness). Cells of the two strains were ovoid to rod-shaped, 0.4-0.8 µm wide and 1.0-2.5 µm long, and motile by means of a polar flagellum. They contained internal photosynthetic membranes of vesicular type and photosynthetic pigments (bacteriochlorophyll a and carotenoids of the spheroidene series). The strains were obligate haloalkaliphiles, growing over wide ranges of salinity (0.3-10.0% NaCl) and pH (7.5-10.0), with growth optima at 1.0-3.0% NaCl and pH 8.5-9.0. Photoheterotrophic and chemoheterotrophic growth occurred with a number of organic compounds and biotin, p-aminobenzoate, thiamine and niacin as growth factors. No anaerobic respiration on nitrite, nitrate or fumarate and no fermentation were demonstrated. The strains grew photolithoautotrophically 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 the electron donor was observed. The major fatty acid was C(18:1) (78%). The major quinone was ubiquinone Q-10. The DNA G+C content of strain A-36s(T) was 65.4 mol% (T(m)). According to genotypic and phenotypic characteristics, the investigated strains were assigned to a novel species of the genus Rhodovulum, for which the name Rhodovulum tesquicola sp. nov. is proposed. The type strain is A-36s(T) ( = VKM B-2491(T) = ATCC BAA-1573(T)), which was isolated from steppe soda lake Sul'fatnoe (Zabaikal'skii Krai, southern Siberia, Russia).

Removal of heavy metals by exopolymeric substances produced by resistant purple nonsulfur bacteria isolated from contaminated shrimp ponds

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Flux balance analysis of photoheterotrophic growth of purple nonsulfur bacteria relevant to biohydrogen production

Purple nonsulfur bacteria can produce hydrogen during photoheterotrophic growth on a variety of organic substrates. To facilitate metabolic engineering of this group of bacteria with the purpose of maximizing hydrogen production, we have developed the first comprehensive mathematical model of anaerobic photoheterotrophic metabolism. This model is a stoichiometric model to which Flux Balance Analysis also known as constraint-based analysis has been applied. Because Rhodobacter sphaeroides emerged as one of the best understood purple nonsulfur bacteria, we based our modeling on this species. However, the approach is readily applicable to other purple nonsulfur bacteria. The metabolic space used in model construction contains 314 reconstructed biochemical reactions and 287 compounds. The list of simulated metabolic pathways involves major carbon and nitrogen metabolic pathways. A distinctive feature of our model is that it considers maximization of two different cell objective functions, namely, biomass production rate, which is commonly used in flux balance models, and reductant removal rate, which is a unique feature of this model reflecting peculiarity of photoheterotrophic metabolism. The performance of this model has been assessed by comparing computed metabolic fluxes with experimental values obtained by several research groups who worked on various strains of purple nonsulfur bacteria and utilized different growth setups. The model testing revealed remarkably good agreement between the predicted and measured metabolic fluxes, which validates the presented model.

Factors affecting immobilization of heavy metals by purple nonsulfur bacteria isolated from contaminated shrimp ponds

In order to remove heavy metals (HMs) from contaminated shrimp pond at the highest concentrations found of; 0.75 mg/l Cd2+, 62.63 mg/l Pb2+, 34.60 mg/l Cu2+ and 58.50 mg/l Zn2+, two strains of purple nonsulfur bacteria isolated from shrimp ponds (NW16 and KMS24) were investigated for their ability to immobilize HMs in 3% NaCl in both microaerobic-light and aerobic-dark conditions. Based on metabolic inhibition and metabolic-dependent studies, it was concluded that both strains removed HMs using biosorption and also bioaccumulation. The efficiency of removal by both strains with both incubating conditions tested was in the order of lead (Pb) > copper (Cu) > zinc (Zn) > cadmium (Cd). Optimal conditions for removal of HMs by strain NW16 were; cells in the log phase at 4.5 mg DCW/ml, pH 6.0, and 30°C for 30 min. With microaerobic-light conditions, the relative percent removal of HMs was: Pb, 83; Cu, 59; Zn, 39; Cd, 23 and slightly more with the aerobic-dark conditions (Pb, 90; Cu, 69; Zn, 46; Cd, 28). Cells in the log phase at 5.0 mg DCW/ml, pH 5.5, and 35°C for 45 min were optimal conditions for strain KMS24 and there were no significant differences for the removal percentages of HMs with either incubating conditions (averages: Pb, 96; Cu, 75; Zn, 46; Cd, 30). The presence of Ca2+ and Mg2+ significantly decreased the removal capacity of HMs for both strains.

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 (Zabaikal'skii Krai, southern Siberia, Russia).

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 (M.I.S). 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 the isolates to known species and for revealing new taxa.

Ecological role of thiosulfate and sulfide utilizing purple nonsulfur bacteria of a riverine ecosystem

The screening of purple nonsulfur bacteria (PNSB) from the polluted and unpolluted zones of the river Ganga and from the discharged effluents (pollutants), revealed that the population densities of PNSB were highest in the discharged pollutants followed by polluted and unpolluted river waters in decreasing order. The allochthonous input of PNSB affected the ambient PNSB population. In all the monitored sites, the PNSB population utilizing malate as electron donor was higher than those utilizing thiosulfate or sulfide or both as electron donors. The physico-chemical parameters of the river water related to the distribution of PNSB were recorded. Twenty-four isolates of PNSB utilizing sulfide and thiosulfate, assigned to Rhodopseudomonas palustris including a morphophysiological variant of the species, Rhodobacter capsulatus and Rhodocyclus gelatinosus (=Rubrivivax gelatinosus), were screened from river Ganga. The surviving ability of PNSB population under simulated condition differed amongst the monitored sites. The isolated strains of PNSB were able to convert thiosulfate to sulfate or to elemental sulfur and also were able to oxidize sulfide. However, there was heterogeneity with respect to the rates at which they transformed these sulfur compounds. The overall thiosulfate transformation rate by the PNSB isolates in the river water was 117.3 μmol d−1 mg−1 and that of sulfide transformation was in the order of 0.15 μmol d−1 mg−1. The ecological significance of sulfide utilization in the aquatic bodies by the isolates of PNSB is discussed.

Rhodobaca bogoriensis gen. nov. and sp. nov., an alkaliphilic purple nonsulfur bacterium from African Rift Valley soda lakes.

From enrichment cultures established for purple nonsulfur bacteria using water and sediment samples from Lake Bogoria and Crater Lake, two soda lakes in the African Rift Valley, three strains of purple nonsulfur bacteria were isolated; strain LBB1 was studied in detail. Cells of strain LBB1 were motile and spherical to rod-shaped, suggesting a relationship to Rhodobacter or Rhodovulum species, and the organism was capable of both phototrophic and chemotrophic growth on a wide variety of organic compounds. Phototrophically grown cultures were yellow to yellow-brown in color and grew optimally at pH 9 (pH range 7.5-10) and 1% NaCl (range 0-10%). In physiological studies of strain LBB1, neither photoautotrophy (H2- or sulfide-dependent) nor nitrogen fixation was observed. Absorption spectra revealed that all three strains contained bacteriochlorophyll a and carotenoids of the spheroidene pathway and synthesized only a light-harvesting (LH) I-type photosynthetic antenna complex. Electron microscopy of cells of strain LBB1 revealed a vesicular intracytoplasmic membrane system, although only a few vesicles were observed per cell. The G+C content of strain LBB1 DNA was 59 mol%, significantly lower than that of known Rhodobacter and Rhodovulum species, and its phylogeny as determined by ribosomal RNA gene sequencing placed it within the Rhodobacter/Rhodovulum clade yet distinct from all described species of either of these genera. The unique assemblage of properties observed in strain LBB1 warrants its inclusion in a new genus of purple nonsulfur bacteria and the name Rhodobaca bogoriensis is proposed herein, the genus name reflecting morphological characteristics and the species epithet referring to the habitat.

Using fluorine-induced chemiluminescence to detect organo-metalloids the headspace of phototrophic bacterial cultures amended with selenium and tellurium

Purple nonsulfur bacteria are resistant to metalloid oxyanions. The key to this resistance seems to lie in their ability to reduce and, in some cases, methylate these toxic chemical species. Six strains of purple nonsulfur bacteria have been grown under photo-heterotrophic conditions and exposed to varied concentrations of inorganic forms of selenium, tellurium and dimethyl selenone, a proposed biological intermediate of the selenium reduction/methylation process. Selenium and tellurium metallic powders have also been added to live cultures. All of the phototrophic bacteria studied here reduce and methylate one or the other oxyanion of Se used, and three strains reduce and methylate Te° and Se°. All strains respond to the addition of dimethyl selenone by producing dimethyl selenide and/or dimethyl diselenide. In all six cases the highest amounts of volatile selenium compounds are found in cultures amended with dimethyl selenone and the lowest amounts in cultures doped with selenate. Some of the phototrophic bacteria studied here, when amended with oxyanions of both Se and Te, increase their release of dimethyl telluride (produced by their bioreduction and methylation of tellurate) in the presence of selenate. Control experiments show that this synergism is biological and not merely caused by the presence of other organo-sulfides or -selenides in culture.

Ecological role of thiosulfate and sulfide utilizing purple nonsulfur bacteria of a riverine ecosystem

The screening of purple nonsulfur bacteria (PNSB) from the polluted and unpolluted zones of the river Ganga and from the discharged effluents (pollutants), revealed that the population densities of PNSB were highest in the discharged pollutants followed by polluted and unpolluted river waters in decreasing order. The allochthonous input of PNSB affected the ambient PNSB population. In all the monitored sites, the PNSB population utilizing malate as electron donor was higher than those utilizing thiosulfate or sulfide or both as electron donors. The physico-chemical parameters of the river water related to the distribution of PNSB were recorded. Twenty-four isolates of PNSB utilizing sulfide and thiosulfate, assigned to Rhodopseudomonas palustris including a morphophysiological variant of the species, Rhodobacter capsulatus and Rhodocyclus gelatinosus (= Rubrivivax gelatinosus), were screened from river Ganga. The surviving ability of PNSB population under simulated condition differed amongst the monitored sites. The isolated strains of PNSB were able to convert thiosulfate to sulfate or to elemental sulfur and also were able to oxidize sulfide. However, there was heterogeneity with respect to the rates at which they transformed these sulfur compounds. The overall thiosulfate transformation rate by the PNSB isolates in the river water was 117.3 μmol d −1 mg −1 and that of sulfide transformation was in the order of 0.15 μmol d −1 mg −1. The ecological significance of sulfide utilization in the aquatic bodies by the isolates of PNSB is discussed.

DNA-DNA Hybridization Studies on Some Purple Nonsulfur Bacteria

Summary The relatedness of some strains of purple nonsulfur bacteria has been studied by DNA-DNA hybridization. Values of 30–100% homology were found between strains of the same species. Strains of different species exhibited 7–18% homology. The genomic relatedness of the group of halophilic strains studied indicates that they merit separate species status. The results agree well with data from 16 S rRNA sequences, cytochrome c structure and rRNA-DNA hybridization studies all of which support recent changes in the classification of the purple nonsulfur bacteria.

Electrophoretic Analysis of Lipopolysaccharides of Purple Nonsulfur Bacteria

Sodium deoxycholate gel electrophoresis was used to analyze the lipopolysaccharides of a variety of species and strains of purple nonsulfur bacteria. The electrophoretic migration patterns found for various lipopolysaccharides indicated their S or R characters, differences in their O-chain lengths, the presence or absence of unsubstituted core stubs, and the approximate sizes of the repeating units. The gel patterns were similar for closely related species (e.g., Rhodopseudomonas viridis and Rhodopseudomonas sulfoviridis or Rhodocyclus tenuis and Rhodocyclus purpureus). Species-specific migration patterns were noted for Rhodocyclus gelatinosus and Rhodopseudomonas viridis. Identical electrophoretic mobilities were observed for different chemo-/serotypes within the same species (e.g., Rhodopseudomonas palustris, Rhodobacter sphaeroides, and Rhodocyclus tenuis). A good correlation between chemo-serotypes and migration patterns was observed. Thus, gel electrophoresis of lipopolysaccharides proved to be useful for chemotaxonomic investigations.