Phototrophic Purple Nonsulfur Bacterium Research Articles

Construction of a Rhodobacter sphaeroides Strain That Efficiently Produces Hydrogen Gas from Acetate without Poly(β-Hydroxybutyrate) Accumulation: Insight into the Role of PhaR in Acetate Metabolism.

The purple nonsulfur phototrophic bacterium Rhodobacter sphaeroides produces hydrogen gas (H2) from acetate. An approach to improve the H2 production is preventing accumulation of an intracellular energy storage molecule known as poly(β-hydroxybutyrate) (PHB), which competes with H2 production for reducing power. However, disruption of PHB biosynthesis has been reported to severely impair the acetate assimilation depending on the genetic backgrounds and/or culture conditions. To solve this problem, we analyzed the relationship between PHB accumulation and acetate metabolism in R. sphaeroides. Gene deletion analyses based on the wild-type strain revealed that among the two polyhydroxyalkanoate synthase genes in the genome, phaC1, but not phaC2, is essential for PHB accumulation, and the phaC1 deletion mutant exhibited slow growth with acetate. On the other hand, a strain with the deletion of phaC1 together with phaR, which encodes a transcriptional regulator capable of sensing PHB accumulation, exhibited growth comparable to that of the wild-type strain despite no accumulation of PHB. These results suggest that PHB accumulation is required for normal growth with acetate by altering the expression of genes under the control of phaR. This hypothesis was supported by a transcriptome sequencing (RNA-seq) analysis revealing that phaR is involved in the regulation of the ethylmalonyl coenzyme A pathway for acetate assimilation. Consistent with these findings, deletion of phaC1 in a genetically engineered H2-producing strain resulted in lower H2 production from acetate due to growth defects, whereas deletion of phaR together with phaC1 restored growth with acetate and increased H2 production from acetate without PHB accumulation. IMPORTANCE This study provides a novel approach for increasing the yield of photofermentative H2 production from acetate by purple nonsulfur phototrophic bacteria. This study further suggests that polyhydroxyalkanoate is not only a storage substance for carbon and energy in bacteria, but may also act as a signaling molecule that mediates bacterial metabolic adaptations to specific environments. This notion will be helpful for understanding the physiology of polyhydroxyalkanoate-producing bacteria, as well as for their metabolic engineering via synthetic biology.

Potential of Phototrophic Purple Nonsulfur Bacteria to Fix Nitrogen in Rice Fields.

Biological nitrogen fixation catalyzed by Mo-nitrogenase of symbiotic diazotrophs has attracted interest because its potential to supply plant-available nitrogen offers an alternative way of using chemical fertilizers for sustainable agriculture. Phototrophic purple nonsulfur bacteria (PNSB) diazotrophically grow under light anaerobic conditions and can be isolated from photic and microaerobic zones of rice fields. Therefore, PNSB as asymbiotic diazotrophs contribute to nitrogen fixation in rice fields. An attempt to measure nitrogen in the oxidized surface layer of paddy soil estimates that approximately 6–8 kg N/ha/year might be accumulated by phototrophic microorganisms. Species of PNSB possess one of or both alternative nitrogenases, V-nitrogenase and Fe-nitrogenase, which are found in asymbiotic diazotrophs, in addition to Mo-nitrogenase. The regulatory networks control nitrogenase activity in response to ammonium, molecular oxygen, and light irradiation. Laboratory and field studies have revealed effectiveness of PNSB inoculation to rice cultures on increases of nitrogen gain, plant growth, and/or grain yield. In this review, properties of the nitrogenase isozymes and regulation of nitrogenase activities in PNSB are described, and research challenges and potential of PNSB inoculation to rice cultures are discussed from a viewpoint of their applications as nitrogen biofertilizer.

Anaerobic 3-methylhopanoid production by an acidophilic photosynthetic purple bacterium

Bacterial lipids are well-preserved in ancient rocks and certain ones have been used as indicators of specific bacterial metabolisms or environmental conditions existing at the time of rock deposition. Here we show that an anaerobic bacterium produces 3-methylhopanoids, pentacyclic lipids previously detected only in aerobic bacteria and widely used as biomarkers for methane-oxidizing bacteria. Both Rhodopila globiformis, a phototrophic purple nonsulfur bacterium isolated from an acidic warm spring in Yellowstone, and a newly isolated Rhodopila species from a geochemically similar spring in Lassen Volcanic National Park (USA), synthesized 3-methylhopanoids and a suite of related hopanoids and contained the genes encoding the necessary biosynthetic enzymes. Our results show that 3-methylhopanoids can be produced under anoxic conditions and challenges the use of 3-methylhopanoids as biomarkers of oxic conditions in ancient rocks and as prima facie evidence that methanotrophic bacteria were active when the rocks were deposited.

Distribution of Phototrophic Purple Nonsulfur Bacteria in Massive Blooms in Coastal and Wastewater Ditch Environments.

The biodiversity of phototrophic purple nonsulfur bacteria (PNSB) in comparison with purple sulfur bacteria (PSB) in colored blooms and microbial mats that developed in coastal mudflats and pools and wastewater ditches was investigated. For this, a combination of photopigment and quinone profiling, pufM gene-targeted quantitative PCR, and pufM gene clone library analysis was used in addition to conventional microscopic and cultivation methods. Red and pink blooms in the coastal environments contained PSB as the major populations, and smaller but significant densities of PNSB, with members of Rhodovulum predominating. On the other hand, red-pink blooms and mats in the wastewater ditches exclusively yielded PNSB, with Rhodobacter, Rhodopseudomonas, and/or Pararhodospirillum as the major constituents. The important environmental factors affecting PNSB populations were organic matter and sulfide concentrations and oxidation–reduction potential (ORP). Namely, light-exposed, sulfide-deficient water bodies with high-strength organic matter and in a limited range of ORP provide favorable conditions for the massive growth of PNSB over co-existing PSB. We also report high-quality genome sequences of Rhodovulum sp. strain MB263, previously isolated from a pink mudflat, and Rhodovulum sulfidophilum DSM 1374T, which would enhance our understanding of how PNSB respond to various environmental factors in the natural ecosystem.

Wastewater bioremediation with using of phototrophic non-sulfur bacteria Rhodopseudomonas yavorovii IMV B-7620

Phototrophic purple non-sulfur bacteria (PNSB) mineralize organic waste. In media with different organic substances they are metabolized from simple aliphatic organic acids to complex polysaccharides. These bacteria can produce H2, indole-3-acetic acid and 5-aminolevulinic acid. PNSB purify waters from hydrogen sulfide and, as components of ecosystem trophic chains, participate in process of sulfur cycle. The ability of these bacteria to denitrification is of particular interest to specialists because nitrates concentrations in industrial effluents are often much higher than the maximum permissible concentrations. The use of industrial, agricultural and household wastes to produce PNSB biomass is economically profitable. Therefore, the aim of our work was to investigate the influence of wastewater of the yeast plant and the water of the settler № 3 filtrate of the Lviv Solid Household Waste Landfill (LSHWL) on the biomass accumulation by PNSB Rhodopseudomonas yavorovii IMV B-7620 and the changes in the composition of these waters in the process of cultivation of the investigated bacteria. Bacteria were grown for 21 days anaerobically at an illumination intensity of 200 lux in 500 ml flasks at +29 ... +30 °C. The wastewater of the yeast plant and the water of the settler № 3 filtrate of the LSHWL were used as the cultivation media. Water was diluted at 10; 30; 50; 100 times. In water, diluted at 10 times, the pH, total ferrum content, Ca2+, Mg2+, Cl-, NO3-, NO2-, SO42-, HS- and chemical oxygen demand (COD) were determined. The biomass of bacteria was measured turbidimetrically at λ = 660 nm. The concentration of HS- was determined spectrophotometrically (λ = 665 nm) by the formation of methylene blue. The content of sulfate ions was determined turbidimetrically (λ = 520 nm) after their precipitation with barium chloride. The concentrations of Ca2+ and Mg2+ were determined titrometrically by reaction with trilon B; Na+ and K+ were analyzed by flame emission spectrometry method (lK = 768 nm, lNa = 589 nm). The pH of the water was measured potentiometrically. The concentration of Cl- was determined titrometrically by reaction with AgNO3. The concentration of nitrite ions was determined spectrophotometrically by the method of sulfanilic acid diazotization by nitrite ions and the interaction of the formed salt with n-(naphthyl)ethylenediamine dihydrochloride (λ = 540 nm, l = 10 mm). The concentration of nitrate ions was determined spectrophotometrically by the diazotization method. Zinc powder was used as the reducing agent. COD was measured with using of KMnO4. It is characterised the patterns of biomass accumulation by R. yavorovii IMV B-7620 bacteria in the wastewater of the yeast plant and the water of the settler № 3 filtrate of the LSHWL, diluted at 10–100 times. The optimal dilution (at 10 times) of water for bacteria cultivation was selected. Bacteria R. yavorovii IMV B-7620 accumulate biomass of 2.2 g/l during growth in a yeast plant wastewater that is twice as large as the biomass, accumulated by bacteria in the diluted water of the settler № 3 filtrate. The organic compounds oxidation efficiency of the yeast plant wastewater and of the settler № 3 filtrate of LSHWL, determined by chemical oxygen demand, was 42.3 and 65.6 %, respectively, on the 21st day of cultivation. The established possibility of the influence of R. yavorovii IMV B-7620 on the decreasing of the content of total Fe, Ca2+, Mg2+, NO3-, NO2-, SO42-, Cl-, HS- in wastewater has complemented and broadened the understanding of the role of purple non-sulfur bacteria in ecosystems, which can significantly influence on the biogeochemical cycles of these compounds in nature. The results obtained may form the basis for the development of effective biotechnologies for wastewater treatment from hydrogen sulfide, chlorine, ferrum, nitrogen, sulfur compounds with the participation of these microorganisms.

Performance and bacterial diversity of bioreactors used for simultaneous removal of sulfide, solids and organic matter from UASB reactor effluents.

Two bioreactors were investigated as an alternative to post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor treating domestic sewage, with an aim of oxidizing sulfide into elemental sulfur, and removal of solid and organic material. The bioreactors were operated at different hydraulic retention times (HRTs) (6, 4, and 2 h) and in the presence or absence (control) of packing material (polypropylene rings). Greater sulfide removal efficiencies - 75% (control reactor) and 92% (packed reactor) - were achieved in both reactors for an HRT of 6 h. Higher organic matter (COD) and solid (TSS) removal levels were observed in the packed reactor, which produced effluent with low COD (100 mg CODL-1) and TSS concentrations (30 mg TSSL-1). Denaturing gradient gel electrophoresis results revealed that a metabolically diverse bacterial community was present in both bioreactors, with sequences related to heterotrophic bacteria, sulfur bacteria (Thiocapsa, Sulfurimonas sp., Chlorobaculum sp., Chromatiales and Sulfuricellales), phototrophic purple non-sulfur bacteria (Rhodopseudomonas, Rhodocyclus sp.) and cyanobacteria. The packed reactor presented higher extracellular sulfur formation and potential for elemental sulfur recovery was seen. Higher efficiencies related to the packed reactor were attributed to the presence of packing material and higher cell retention time. The studied bioreactors seemed to be a simple and low-cost alternative for the post-treatment of anaerobic effluent.

Whole-genome sequencing and comparative analysis of two plant-associated strains of Rhodopseudomonas palustris (PS3 and YSC3)

Rhodopseudomonas palustris strains PS3 and YSC3 are purple non-sulfur phototrophic bacteria isolated from Taiwanese paddy soils. PS3 has beneficial effects on plant growth and enhances the uptake efficiency of applied fertilizer nutrients. In contrast, YSC3 has no significant effect on plant growth. The genomic structures of PS3 and YSC3 are similar; each contains one circular chromosome that is 5,269,926 or 5,371,816 bp in size, with 4,799 or 4,907 protein-coding genes, respectively. In this study, a large class of genes involved in chemotaxis and motility was identified in both strains, and genes associated with plant growth promotion, such as nitrogen fixation-, IAA synthesis- and ACC deamination-associated genes, were also identified. We noticed that the growth rate, the amount of biofilm formation, and the relative expression levels of several chemotaxis-associated genes were significantly higher for PS3 than for YSC3 upon treatment with root exudates. These results indicate that PS3 responds better to the presence of plant hosts, which may contribute to the successful interactions of PS3 with plant hosts. Moreover, these findings indicate that the existence of gene clusters associated with plant growth promotion is required but not sufficient for a bacterium to exhibit phenotypes associated with plant growth promotion.

Restricted Localization of Photosynthetic Intracytoplasmic Membranes (ICMs) in Multiple Genera of Purple Nonsulfur Bacteria.

ABSTRACTIn bacteria and eukaryotes alike, proper cellular physiology relies on robust subcellular organization. For the phototrophic purple nonsulfur bacteria (PNSB), this organization entails the use of a light-harvesting, membrane-bound compartment known as the intracytoplasmic membrane (ICM). Here we show that ICMs are spatially and temporally localized in diverse patterns among PNSB. We visualized ICMs in live cells of 14 PNSB species across nine genera by exploiting the natural autofluorescence of the photosynthetic pigment bacteriochlorophyll (BChl). We then quantitatively characterized ICM localization using automated computational analysis of BChl fluorescence patterns within single cells across the population. We revealed that while many PNSB elaborate ICMs along the entirety of the cell, species across as least two genera restrict ICMs to discrete, nonrandom sites near cell poles in a manner coordinated with cell growth and division. Phylogenetic and phenotypic comparisons established that ICM localization and ICM architecture are not strictly interdependent and that neither trait fully correlates with the evolutionary relatedness of the species. The natural diversity of ICM localization revealed herein has implications for both the evolution of phototrophic organisms and their light-harvesting compartments and the mechanisms underpinning spatial organization of bacterial compartments.

Oligomeric forms of bacterial malate dehydrogenase: a study of the enzyme from the phototrophic non-sulfur bacterium Rhodovulum steppense A-20s.

Malate dehydrogenase (EC 1.1.1.37) was purified to homogeneity from the phototrophic purple non-sulfur bacterium Rhodovulum steppense A-20s. According to gel-chromatography and electrophoretic studies, malate dehydrogenase is present as a dimer, tetramer and octamer depending on cultivation conditions. In phototrophic aerobic conditions only the tetrameric form was present, in chemotrophic aerobic conditions all three forms were detected, while in the absence of oxygen the octameric form disappeared. The malate dehydrogenase oligomers are encoded by a single gene and composed of the same 35kDa polypeptide but differ in pH and temperature optimum, in affinities to malate, oxaloacetate, NADH and NAD+ and in regulation by cations and citrate. By modulating the cultivation conditions, it has been established that the dimer participates in the glyoxylate cycle; the tetramer operates in the tricarboxylic acid cycle, and the octamer may be involved in the adaptation to oxidative stress.

Clades of Photosynthetic Bacteria Belonging to the Genus Rhodopseudomonas Show Marked Diversity in Light-Harvesting Antenna Complex Gene Composition and Expression.

Many photosynthetic bacteria have peripheral light-harvesting (LH) antenna complexes that increase the efficiency of light energy capture. The purple nonsulfur photosynthetic bacterium Rhodopseudomonas palustris produces different types of LH complexes under high light intensities (LH2 complex) and low light intensities (LH3 and LH4 complexes). There are multiple pucBA operons that encode the α and β peptides that make up these complexes. However, low-resolution structures, amino acid similarities between the complexes, and a lack of transcription analysis have made it difficult to determine the contributions of different pucBA operons to the composition and function of different LH complexes. It was also unclear how much diversity of LH complexes exists in R.palustris and affiliated strains. To address this, we undertook an integrative genomics approach using 20 sequenced strains. Gene content analysis revealed that even closely related strains have differences in their pucBA gene content. Transcriptome analyses of the strains grown under high light and low light revealed that the patterns of expression of the pucBA operons varied among strains grown under the same conditions. We also found that one set of LH2 complex proteins compensated for the lack of an LH4 complex under low light intensities but not under extremely low light intensities, indicating that there is functional redundancy between some of the LH complexes under certain light intensities. The variation observed in LH gene composition and expression in Rhodopseudomonas strains likely reflects how they have evolved to adapt to light conditions in specific soil and water microenvironments. IMPORTANCERhodopseudomonas palustris is a phototrophic purple nonsulfur bacterium that adapts its photosystem to allow growth at a range of light intensities. It does this by adjusting the amount and composition of peripheral light-harvesting (LH) antenna complexes that it synthesizes. Rhodopseudomonas strains are notable for containing numerous sets of light-harvesting genes. We determined the diversity of LH complexes and their transcript levels during growth under high and low light intensities in 20 sequenced genomes of strains related to the species Rhodopseudomonas palustris. The data obtained are a resource for investigators with interests as wide-ranging as the biophysics of photosynthesis, the ecology of phototrophic bacteria, and the use of photosynthetic bacteria for biotechnology applications.

Isolation and Characterization of L-Tryptophan Ammonia Lyase from Rubrivivax benzoatilyticus Strain JA2.

Ammonia lyase belongs to the family of enzymes that catalyzes the deamination of amino acids. Depending on the relative activity towards the substrates, L-tryptophan ammonia lyase converts L-tryptophan to indole 3-acrylic acid and ammonia. Here, we isolated, purified, and characterized an L-tryptophan ammonia lyase from phototrophic purple non-sulfur bacterium Rubrivivax benzoatilyticus JA2. The isolated L-tryptophan ammonia lyase found to catalyze the reaction of L-tryptophan to produce indole 3-acrylic acid and NH3. The enzyme is a heterotetramer and has the highest affinity to L-tryptophan. The optimum pH and temperature for the enzymatic action were 7.5 and 35°C, respectively and the Km and Vmax were 40.4 ± 23.1 nM and 0.964±0.2046 s(-1), respectively. These results suggest that the isolated enzyme is highly bioactive and could be a new class. Further molecular analyses are required to confirm the novelty of the enzyme.

Posttranslational modification of a vanadium nitrogenase.

In microbes that fix nitrogen, nitrogenase catalyzes the conversion of N2 to ammonia in an ATP-demanding reaction. To help conserve energy some bacteria inhibit nitrogenase activity upon exposure to ammonium. The purple nonsulfur phototrophic bacterium Rhodopseudomonas palustris strain CGA009 can synthesize three functional nitrogenase isoenzymes: a molybdenum nitrogenase, a vanadium nitrogenase, and an iron nitrogenase. Previous studies showed that in some alphaproteobacteria, including R. palustris, molybdenum nitrogenase activity is inhibited by ADP-ribosylation when cells are exposed to ammonium. Some iron nitrogenases are also posttranslationally modified. However, the posttranslational modification of vanadium nitrogenase has not been reported. Here, we investigated the regulation of the alternative nitrogenases of R. palustris and determined that both its vanadium nitrogenase and its iron nitrogenase activities were inhibited and posttranslationally modified when cells are exposed to ammonium. Vanadium nitrogenase is not found in all strains of R. palustris, suggesting that it may have been acquired by horizontal gene transfer. Also, phylogenetic analyses of the three nitrogenases suggest that VnfH, the target of ADP-ribosylation, may be the product of a gene duplication of nifH, the molybdenum nitrogenase homolog.

Use of mixed culture bacteria for photofermentive hydrogen of dark fermentation effluent

Hydrogen production (HP) from dark fermentation effluent of starch wastewater via vertical tubular photo-bioreactor was investigated. The reactor was inoculated with mixed culture of bacteria and operated at light intensity of 190W/m2. Hydraulic retention time (HRT) and organic loading rate (OLR) was varied between 0.9 to 4.0h and 3.2 to 16gCOD/l.d., respectively. Increasing the HRT from 0.9 to 2.5h, significantly (P<0.05) increased HP from 1±0.04 to 3.05±0.19l/d, respectively. However, minimal increase in HP occurred when increasing the HRT up to 4.0h. The HP remained unaffected when increasing the OLR from 3.2 to 6.4gCOD/l.d. Further increase in the OLR up to 8.2 and 16gCOD/l.d., resulted in a drop in HP i.e. 0.96 and 0.19l/d, respectively. Microbial community analysis of the reactor samples showed the presence and dominance of hydrogen producing purple non-sulfur phototrophic (PNS) bacterium, Rhodopseudomonas palustris in the reactor.

Planktonic bacterial community composition of an extremely shallow soda pond during a phytoplankton bloom revealed by cultivation and molecular cloning

Böddi-szék is one of the shallow soda ponds located in the Kiskunság National Park, Hungary. In June 2008, immediately prior to drying out, an extensive algal bloom dominated by a green alga (Oocystis submarina Lagerheim) was observed in the extremely saline and alkaline water of the pond. The aim of the present study was to reveal the phylogenetic diversity of the bacterial communities inhabiting the water of Böddi-szék during the blooming event. Using two different selective media, altogether 110 aerobic bacterial strains were cultivated. According to the sequence analysis of the 16S rRNA gene, most of the strains belonged to alkaliphilic or alkalitolerant and moderately halophilic species of the genera Bacillus and Gracilibacillus (Firmicutes), Algoriphagus and Aquiflexum (Bacteroidetes), Alkalimonas and Halomonas (Gammaproteobacteria). Other strains were closely related to alkaliphilic and phototrophic purple non-sulfur bacteria of the genera Erythrobacter and Rhodobaca (Alphaproteobacteria). Analysis of the 16S rRNA gene-based clone library indicated that most of the total of 157 clone sequences affiliated with the anoxic phototrophic bacterial genera of Rhodobaca and Rhodobacter (Alphaproteobacteria), Ectothiorhodospira (Gammaproteobacteria) and Heliorestis (Firmicutes). Phylotypes related to the phylum Bacteroidetes formed the second most abundant group. Clones related to the mainly anaerobic and alkaliphilic bacterial genera of Anoxynatronum (Firmicutes), Spirochaeta (Spirochaetes) and Desulfonatronum (Deltaproteobacteria) were also abundant. Further clone sequences showed less than 95% similarity values to cultivated species of the phyla Actinobacteria, Cyanobacteria, Deinococcus-Thermus, Fibrobacteres, Gemmatimonadetes and Lentisphaerae.

English

&nbsp; Six strains of phototrophic purple non-sulfur bacteria were isolated from paddy soil, lake water and pond sediment samples. They showed the ability to produce 5-aminolevulinic acid under anaerobic-light (3,000 lux) condition. A selected strain, designated as PS-5, produced the highest 5-aminolevulinic acid (ALA) concentration (45.10&nbsp;mM) and productivity (0.94&nbsp;mM h-1) in glutamate-malate (GM) medium as well as possessed self-flocculating ability. Based on physiological and 16S rRNA sequence, the isolate PS-5 was identified to be&nbsp;Rubrivivax benzoatilyticus. The optimum concentration of C4&nbsp;pathway precursors was 7.5 mM glycine and 10 mM succinate with supplementation of 10 mM levulinic acid. This resulted in 4.2 fold increase of 5-aminolevulinic acid production to 190.74&nbsp;mM and 2.7-fold increase of its productivity to 2.57&nbsp;mM h-1&nbsp;compared to the control. In addition, the optimum concentration of C5pathway precursor was 50 mM glutamate with the maximum 5-aminolevulinic acid production of 84.12&nbsp;mM and productivity of 1.56&nbsp;mM h-1. Therefore,&nbsp;R. benzoatilyticusPS-5 could produce 5-aminolevulinic acid using both C4&nbsp;and C5&nbsp;pathway precursors and preferred C4&nbsp;pathway over C5&nbsp;pathway as it produced more than 2.3 folds higher 5-aminolevulinic acid concentration. &nbsp; Key words:&nbsp;5-Aminolevulinic acid, photosynthetic bacteria, self-flocculation, optimization,&nbsp;Rubrivivax benzoatilyticus.

Neurosporene is the major carotenoid accumulated by Rhodobacter viridis JA737

The carotenoid, neurosporene, is of commercial importance due to its use as an antioxidant and UV-B radiation protector. It is usually obtained from fruits and vegetables. Although some bacterial mutants can accumulate neurosporene, these are unstable. A recently-isolated, natural and stable neurosporene accumulating, phototrophic purple non-sulfur bacterium Rhodobacter viridis JA737 is described that accumulates neurosporene as the major (98%) carotenoid up to ~7 mg g dry cell(-1) and at 7.3 mg l(-1).

Distribution and Origin of Oxygen-Dependent and Oxygen-Independent Forms of Mg-Protoporphyrin Monomethylester Cyclase among Phototrophic Proteobacteria

Magnesium-protoporphyrin IX monomethylester cyclase is one of the key enzymes of the bacteriochlorophyll biosynthesis pathway. There exist two fundamentally different forms of this enzyme. The oxygen-dependent form, encoded by the gene acsF, catalyzes the formation of the bacteriochlorophyll fifth ring using oxygen, whereas the oxygen-independent form encoded by the gene bchE utilizes an oxygen atom extracted from water. The presence of acsF and bchE genes was surveyed in various phototrophic Proteobacteria using the available genomic data and newly designed degenerated primers. It was found that while the majority of purple nonsulfur bacteria contained both forms of the cyclase, the purple sulfur bacteria contained only the oxygen-independent form. All tested species of aerobic anoxygenic phototrophs contained acsF genes, but some of them also retained the bchE gene. In contrast to bchE phylogeny, the acsF phylogeny was in good agreement with 16S inferred phylogeny. Moreover, the survey of the genome data documented that the acsF gene occupies a conserved position inside the photosynthesis gene cluster, whereas the bchE location in the genome varied largely between the species. This suggests that the oxygen-dependent cyclase was recruited by purple phototrophic bacteria very early during their evolution. The primary sequence and immunochemical similarity with its cyanobacterial counterparts suggests that acsF may have been acquired by Proteobacteria via horizontal gene transfer from cyanobacteria. The acquisition of the gene allowed purple nonsulfur phototrophic bacteria to proliferate in the mildly oxygenated conditions of the Proterozoic era.

Improvement of hydrogen production with Rhodopseudomonas palustris CQK-01 by Ar gas sparging

For improving photo-biohydrogen production, a novel gas bubble column photobioreactor with Ar gas sparging was developed for biohydrogen production by purple non-sulfur phototrophic bacteria, Rhodoseudomonas palustris CQK-01. The dissolved hydrogen concentration was in-situ measured by a hydrogen microsensor. Experimental results demonstrated that Ar gas sparging dramatically decreased the dissolved hydrogen concentration, resulting in an improvement in the photo-biohydrogen production performance. Furthermore, effects of the gas flow rate and the time interval of gas sparging were investigated. The results showed that with an increase in the gas flow rate, the hydrogen production performance increased initially due to the reduced dissolved hydrogen concentration and enhanced mass transport, and then it decreased as a result of an increased shear stress. Meanwhile, the short sparging time interval resulted in a low accumulation of dissolved hydrogen in the bioreactor, hence high hydrogen production performance. The optimal hydrogen production rate (5.86 mmol/l/h) and hydrogen yield (3.38 mol H2/mol glucose) were obtained at the gas flow rate of 10 ml/min, respectively.

Electrochemical regulation of microbial growth on disposable screen printed carbon electrodes

Herein we report an effective method to enhance microbial immobilization on screen-printed carbon electrode (SPCE) surface by electrochemical regulation of redox potential. This technique could deliver a prospective electrode for microbial biofuel cell and other applications. A phototrophic purple nonsulfur bacterium Rhodopseudomonas palustris CGA009 was selected as a model organism to examine the proposed approach. Scanning the electrode between −0.7 to 0.3V (vs. Ag/AgCl) at 70mV/s for 50 cycles (∼24min), placed in the growth medium with bacteria, significantly increased microbial adhesion when compared to SPCE without electrochemical stimulation. The electron-transfer effect between the adsorbed microorganism and electrode surface was further studied by AC impedance spectroscopy to confirm the accelerated microbial immobilization. Stable photosynthetic electron transport chain from immobilized bacteria through SPCE was achieved.

Effect of Substrate pH Value on Hydrogen Production by Photosynthetic Bacteria*

For exploring the hydrogen production mechanism of photosynthetic bacteria,hydrogen production by the purple non-sulfur phototrophic bacterium Rhodoseudomonas palustris CQK-01 illuminated by light-emitting diodes with light wavelength of 470 nm was experimentally investigated in batch culture mode under anaerobic conditions,and the effect of initial substrate pH value on hydrogen production performance and energy conversion efficiencies were discussed.Glucose with concentration of 75 mmol/L was used as carbon source in medium,and the initial substrate pH values were set at 5.5,6.0,7.0,8.0 and 9.0.The light intensity was set at 1 000 lx and operation temperature was 30 ℃.The experimental results showed that the weak alkaline condition was favorable for the growth of photosynthetic bacteria,and after 96 hours' operation for hydrogen production,the total hydrogen production and the maximum hydrogen production rate was 8.0 mmol and 3.39 mmol g-1(cell dry weight) h-1 at the optimal pH 7.0,respectively.The produced hydrogen purity was 70%,and the substrate energy conversion efficiency and light energy conversion efficiency were 1.98% and 7.7%,respectively.It was also found that the substrate energy conversion efficiency,light energy conversion efficiency,hydrogen production and hydrogen production rate were higher in acidic substrate than in alkaline substrate,while the hydrogen purity increased with the increase of initial substrate pH value