Reduction in arsenic toxicity and uptake in rice (Oryza sativa L.) by As-resistant purple nonsulfur bacteria

This study aimed to investigate the potential of Rhodopseudomonas palustris C1 and Rubrivivax benzoatilyticus C31 to ameliorate As toxicity and to reduce As uptake in rice. Strain C1 was superior to strain C31 for siderophore production. The mixed culture (1: 1) was most effective in reducing the toxicity of As species [As(III) and/or As(V), each 30 mg/l] by yielding maximal germination index that related to α- and β-amylase activities in two Thai rice cultivars (HomNil: HN and PathumThani 1: PT). Arsenic toxicity to the seed germination followed the order: mixed As species > As(III) > As(V); and the toxicity was reduced in inoculated sets, particularly with a mixed culture. The mixed culture significantly enhanced rice growth under As stress in both rice cultivars as indicated by an increase in the production of chlorophyll a and b, and also supporting the non-enzymatic (carotenoids, lipid oxidation, and nitric oxide) and enzymatic (superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase) activities. These were concomitant with productions of 5-aminolevulinic acid, indole-3-acetic acid, exopolymeric substances, and siderophores which significantly reduced As accumulation in treated rice. It can be concluded that the mixed culture has great potential to ameliorate rice from As toxicity by preventing As species entry into rice for enhancing rice growth and also for reducing As accumulation to produce safe rice from rice grown in contaminated paddy fields.

Effect of carbon sources on the aggregation of photo fermentative bacteria induced by L-cysteine for enhancing hydrogen production

Poor flocculation of photo fermentative bacteria resulting in continuous biomass washout from photobioreactor is a critical challenge to achieve rapid and stable hydrogen production. In this work, the aggregation of Rhodopseudomonas faecalis RLD-53 was successfully developed in a photobioreactor and the effects of different carbon sources on hydrogen production and aggregation ability were investigated. Extracellular polymeric substances (EPS) production by R. faecalis RLD-53 cultivated using different carbon sources were stimulated by addition of L-cysteine. The absolute ζ potentials of R. faecalis RLD-53 were considerably decreased with addition of L-cysteine, and aggregation barriers based on DLVO dropped to 15-43 % of that in control groups. Thus, R. faecalis RLD-53 flocculated effectively, and aggregation abilities of strain RLD-53 cultivated with acetate, propionate, lactate and malate reached 29.35, 32.34, 26.07 and 24.86 %, respectively. In the continuous test, hydrogen-producing activity was also promoted and reached 2.45 mol H₂/mol lactate, 3.87 mol H₂/mol propionate and 5.10 mol H₂/mol malate, respectively. Therefore, the aggregation of R. faecalis RLD-53 induced by L-cysteine is independent on the substrate types, which ensures the wide application of this technology to enhance hydrogen recovery from wastewater dominated by different organic substrates.

Effects of metal ions on biomass and 5-aminolevulinic acid production in Rhodopseudomonas palustris wastewater treatment

This work investigated the effects of eight metal ions on Rhodopseudomonas palustris growth and 5-aminolevulinic acid (ALA) yield in wastewater treatment. Results show that metal ions (Mg(2+) of 15 mmol/L, Fe(2+) of 400 μmol/L, Co(2+) of 4 μmol/L, Ni(2+) of 8 μmol/L and Zn(2+) of 4 μmol/L) could effectively improve the chemical oxygen demand (COD) removal, Rp. palustris biomass and ALA yield. The highest ALA yield of 13.1 mg/g-biomass was achieved with Fe(2+) of 400 μmol/L. ALA yields were differentially increased under different metal ions in the following order: Fe(2+) group > Mg(2+) group > Co(2+) group = Ni(2+) group > Zn(2+) group = Mo(2+) group > control. Cu(2+) and Mn(2+) inhibited Rp. palustris growth and ALA production. Mechanism analysis revealed that metal ions changed ALA yields by influencing the activities of ALA synthetase and ALA dehydratase.

Purple non-sulfur photosynthetic bacteria monitor environmental stresses

Heavy metal ion pollution and oxygen deficiency are major environmental risks for microorganisms in aqueous habitat. The potential of purple non-sulfur photosynthetic bacteria for biomonitoring and bioremediation was assessed by investigating the photosynthetic capacity in heavy metal contaminated environments. Cultures of bacterial strains Rhodobacter sphaeroides, Rhodospirillum rubrum and Rubrivivax gelatinosus were treated with heavy metal ions in micromolar (Hg(2+)), submillimolar (Cr(6+)) and millimolar (Pb(2+)) concentration ranges. Functional assays (flash-induced absorption changes and bacteriochlorophyll fluorescence induction) and electron micrographs were taken to specify the harmful effects of pollution and to correlate to morphological changes of the membrane. The bacterial strains and functional tests showed differentiated responses to environmental stresses, revealing that diverse mechanisms of tolerance and/or resistance are involved. The microorganisms were vulnerable to the prompt effect of Pb(2+), showed weak tolerance to Hg(2+) and proved to be tolerant to Cr(6+). The reaction center controlled electron transfer in Rvx. gelatinosus demonstrated the highest degree of resistance against heavy metal exposure.

Metabolism of Multiple Aromatic Compounds in Corn Stover Hydrolysate by Rhodopseudomonas palustris

Lignocellulosic biomass hydrolysates hold great potential as a feedstock for microbial biofuel production, due to their high concentration of fermentable sugars. Present at lower concentrations are a suite of aromatic compounds that can inhibit fermentation by biofuel-producing microbes. We have developed a microbial-mediated strategy for removing these aromatic compounds, using the purple nonsulfur bacterium Rhodopseudomonas palustris. When grown photoheterotrophically in an anaerobic environment, R. palustris removes most of the aromatics from ammonia fiber expansion (AFEX) treated corn stover hydrolysate (ACSH), while leaving the sugars mostly intact. We show that R. palustris can metabolize a host of aromatic substrates in ACSH that have either been previously described as unable to support growth, such as methoxylated aromatics, and those that have not yet been tested, such as aromatic amides. Removing the aromatics from ACSH with R. palustris, allowed growth of a second microbe that could not grow in the untreated ACSH. By using defined mutants, we show that most of these aromatic compounds are metabolized by the benzoyl-CoA pathway. We also show that loss of enzymes in the benzoyl-CoA pathway prevents total degradation of the aromatics in the hydrolysate, and instead allows for biological transformation of this suite of aromatics into selected aromatic compounds potentially recoverable as an additional bioproduct.

The purification of crude glycerol derived from biodiesel manufacture and its use as a substrate by Rhodopseudomonas palustris to produce hydrogen

Crude glycerol (CG) from biodiesel production is often contaminated with several compounds, including saponified fatty acids (SFAs). Photofermentative growth of Rhodopseudomonas palustris on glycerol leads to hydrogen production; however, R. palustris is inhibited by SFAs. This study examines inhibition of R. palustris by SFAs, finding that, with increasing concentration of SFA, growth rate falls, reaching zero at an SFA concentration of 0.2 mM. Methods for purifying CG were examined, namely (i) treatment with ethanol and activated carbon, (ii) pH adjustment, (iii) solvent extraction, and (iv) precipitation of the fatty acids with calcium. The rates of growth and production of hydrogen were investigated using CG treated by these methods. It was found that treatment with activated carbon, pH reduction, and calcium precipitation reduced inhibition, while solvent extraction was effective only when used in conjunction with pH adjustment. These treatments allow crude glycerol to be used for hydrogen production by R. palustris.

Bioconversion characteristics of Rhodopseudomonas palustris CQK 01 entrapped in a photobioreactor for hydrogen production

The performance of the entrapped-cell photobioreactor during H2 production was assessed by using glucose as substrate in a continuous operation mode. The maximal hydrogen production rate and light conversion efficiency, 2.61 mmol/L/h and 82.3%, were obtained at a HRT of 11.4 h, an substrate loading rate of 4.2 mmol/h and an illumination of 590 nm and 6000 lux, the corresponding hydrogen yield and total energy efficiency were 0.62 mmol H2/(mmol glucose) and 4.8%, respectively. The results indicate the H2 production system illuminated at 590 nm wavelength engaged in energy storage for H2 production due to more ATP synthesized in primary reaction center, and was of higher energy recovery capacity. Furthermore, the total energy efficiency was far lower than the corresponding light conversion efficiency due to intermediates production.

Nano-TiO2 enhanced photofermentative hydrogen produced from the dark fermentation liquid of waste activated sludge

After anaerobic dark fermentation of waste activated sludge (WAS) for hydrogen production, there are a large number of organic compounds including protein, polysaccharide, and volatile fatty acids left in the dark fermentation liquid, which can be further bioconverted to hydrogen by photofermentation techniquea. In this study, the enhancement of photofermentative hydrogen produced from WAS dark fermentation liquid by using nano-TiO2 is reported. First, high concentration of NH(4)(+)-N in the dark fermentation liquid was observed to inhibit the photofermentative hydrogen production, and its removal was essential. Then the effect of nano-TiO2 on photofermentative hydrogen generation was investigated, and the addition of 100 mg/L nano-TiO2 increased hydrogen by 46.1%. Finally, the mechanisms for nano-TiO2 improving hydrogen production were investigated. It was found that nano-TiO2 improved the decomposition of protein and polysaccharide to small-molecule organic compounds and promoted the growth of photosynthetic bacteria and the activity of nitrogenase but decreased the H2-uptake hydrogenase activity.

Hydrogen production by Rhodopseudomonas palustris WP 3-5 in a serial photobioreactor fed with hydrogen fermentation effluent

In this study, a lab-scale serial photobioreactor composed of three column reactors was constructed and continuously operated to investigate several parameters influencing photohydrogen production when using the synthetic wastewater and the anaerobic hydrogen fermentation effluents as the influents. The results indicated that better hydrogen production rate was obtained when the serial photobioreactor was operated under cellular recycling at a short HRT of 8h. The serial photobioreactor maintained high hydrogen content ca. 80% in the produced gas and 0.4× dilution ratio was the suitable ratio for hydrogen production. When the photobioreactor fed with the real wastewater (Effluent 1) containing 100 mg/L NH4Cl, Column 1 reactor successfully reduced ammonia concentration to about 60 mg/L for cell synthesis, resulting in a steady hydrogen production in the following two column reactors. The average hydrogen production rate was 205 mL-H2/L/d.

Improved phototrophic H2 production with Rhodopseudomonas palustris WP3-5 using acetate and butyrate as dual carbon substrates

An indigenous purple nonsulfur bacterium Rhodopseudomonas palustris WP3-5 was used to produce hydrogen phototrophically from acetate (HAc) and butyrate (HBu), which are the major soluble products from acidogenic dark fermentation. Statistical experimental design methodology was applied to identify optimal composition of the two carbon substrates in the medium, leading to better H2 production performance of R. palustris WP3-5. Three performance indexes were used to assess the effectiveness of the phototrophic H2 production; they were H2 yield (Y H2), maximum H2 production rate (Rmax) and maximum cumulative H2 evolution (Hmax). An overlay contour plot was used to determine the optimal concentration range of HAc and HBu, taking into account all three performance indexes (i.e., Rmax, Hmax, and Y H2) simultaneously. With the response surface analysis, R. palustris WP3-5 could produce H2 efficiently with the best Rmax, Hmax, and Y H2 of 39.5 ml/h, 2738 ml, and 51.6%, respectively. This performance is superior to most reported values in the literature, indicating that the statistical experimental design is an effective tool to improve phototrophic H2 production with R. palustris WP3-5.

Evolution of a bacteriophytochrome from light to redox sensor

Bacteriophytochromes are red/far-red photoreceptors that bacteria use to mediate sensory responses to their light environment. Here, we show that the photosynthetic bacterium Rhodopseudomonas palustris has two distinct types of bacteriophytochrome-related protein (RpBphP4) depending upon the strain considered. The first type binds the chromophore biliverdin and acts as a light-sensitive kinase, thus behaving as a bona fide bacteriophytochrome. However, in most strains, RpBphP4 does not to bind this chromophore. This loss of light sensing is replaced by a redox-sensing ability coupled to kinase activity. Phylogenetic analysis is consistent with an evolutionary scenario, where a bacteriophytochrome ancestor has adapted from light to redox sensing. Both types of RpBphP4 regulate the synthesis of light harvesting (LH2) complexes according to the light or redox conditions, respectively. They modulate the affinity of a transcription factor binding to the promoter regions of LH2 complex genes by controlling its phosphorylation status. This is the first complete description of a bacteriophytochrome signal transduction pathway involving a two-component system.

Augmentation of H2 photoproduction in Rhodopseudomonas palustris by N-heterocyclic aromatic compounds

Increases of 23- (5.6 mmol acetylene reduced mg dry wt(-1)) and 16- (4 mmol acetylene reduced mg dry wt(-1)) fold in nitrogenase activity and 12- (671 microl H2 mg dry wt(-1) h(-1)) and 6- (349 microl mg dry wt(-1) h(-1)) fold in H2 photoproduction in Rhodopseudomonas palustris JA1 over 24 h were achieved with pyrazine 2-carboxylate (3 mM) and 3-picoline (3 mM), respectively, and were higher than earlier reports of enhancement (1.5 to 5-fold) in biological H2 production using various alternative methods.

[Hydrogen photoproduction from acetate by Rhodopseudomonas palustris]

Based on the characteristics of metabolism of photosynthetic bacteria and the major kinds of organic compounds produced in wastewater degradation, eleven kinds of organic compounds were chosen for hydrogen photoproduction using Rhodopseudomonas palustris Z strain. The maximal volumetric H2 productivity was obtained using acetate as the sole carbon source and electron donor. The kinetics of cell growth and H2 liberation, and the influences of several major limiting factors on photoevolution of H2 were examined using acetate as carbon source. It was shown that hydrogen production was partially correlated with cell growth. The medium composition of the preculture, the preculture time, and inoculation volume were confirmed to have big effects on hydrogen photoevolution. The time delay of H2 production was evidently shortened using the inoculum of late exponential growth phase or stationary phase using ammonium sulfate as nitrogen source or with the inoculum of middle exponential growth phase using glutamate as the nitrogen source. The identity of temperature and light intensity for H2 evolution and cell growth has significant potential application in the technology of splitting organic acid into H2 by photosynthetic bacteria. The concentrations of acetate and glutamate in the medium affected hydrogen photoevolution and cell growth significantly. The productivity of H2 increased with substrate concentrations when substrate concentrations of sodium acetate and sodium glutamate were lower than 70 mmol/L and 15 mmol/L, respectively. Hydrogen production was inhibited but the cell growth was faster when the concentration of sodium glutamate over 15 mmol/L due to forming free NH4+. The highest rate of hydrogen production was 19.4 mL.L-1.h-1 using 30 mmol/L of sodium acetate as hydrogen donor under the standard conditions, respectively. The optimal conditions for hydrogen production were 35-37 degrees C, 6000-8000 lx and pH 7.3-8.3. The effects of oxygen and inoculation volume on photoproduction of hydrogen were also discussed.

Taxis response of various denitrifying bacteria to nitrate and nitrite

The taxis response of Rhodobacter sphaeroides 2.4.1 and 2.4.3, Rhodopseudomonas palustris, and Agrobacterium tumefaciens to nitrate and nitrite was evaluated by observing the macroscopic behavior of cells suspended in soft agar and incubated under various conditions. R. sphaeroides 2.4.3, which is capable of both nitrate and nitrite reduction, showed a taxis response to both nitrate and nitrite. R. sphaeroides 2.4.1, which contains nitrate reductase but not nitrite reductase, did not show a taxis response towards either nitrogen oxide. Insertional inactivation of the nitrite reductase structural gene or its transcriptional regulator, NnrR, in strain 2.4.3 caused a loss of a taxis response towards both nitrate and nitrite. An isolate of 2.4.1 carrying a copy of the nitrite reductase gene from 2.4.3 showed a taxis response to both nitrogen oxides. The taxis response of 2.4.3 was observed under anaerobic conditions, suggesting that the taxis response was due to nitrate and nitrite respiration, not to inhibition of oxygen respiration by respiration of nitrogen oxides. Strain 2.4.3 showed a taxis response to nitrate and nitrite under photosynthetic and aerobic conditions. Changing the carbon source in the culture medium caused an unexpected subtle shift in the taxis response of 2.4.3 to nitrite. A taxis response to nitrogen oxides was also observed in R. palustris and A. tumefaciens. R. palustris exhibited a taxis response to nitrite but not to nitrate, while A. tumefaciens exhibited a response to both compounds.

HbaR, a 4-hydroxybenzoate sensor and FNR-CRP superfamily member, regulates anaerobic 4-hydroxybenzoate degradation by Rhodopseudomonas palustris

Under anaerobic conditions, structurally diverse aromatic compounds are catabolized by bacteria to form benzoyl-coenzyme A (benzoyl-CoA), the starting compound for a central reductive pathway for aromatic ring degradation. The structural genes required for the conversion of 4-hydroxybenzoate (4-HBA) to benzoyl-CoA by Rhodopseudomonas palustris have been identified. Here we describe a regulatory gene, hbaR, that is part of the 4-HBA degradation gene cluster. An hbaR mutant that was constructed was unable to grow anaerobically on 4-HBA. However, the mutant retained the ability to grow aerobically on 4-HBA by an oxygen-requiring pathway distinct from the anaerobic route of 4-HBA degradation. The effect of the HbaR protein on expression of hbaA encoding 4-HBA-CoA ligase, the first enzyme for 4-HBA degradation, was investigated by using hbaA::'lacZ transcriptional fusions. HbaR was required for a 20-fold induction of beta-galactosidase activity that was observed with a chromosomal hbaA::'lacZ fusion when cells grown anaerobically on succinate were switched to anaerobic growth on succinate and 4-HBA. HbaR also activated expression from a plasmid-borne hbaA-'lacZ fusion when it was expressed in aerobically grown Pseudomonas aeruginosa cells, indicating that the activity of this regulator is not sensitive to oxygen. The deduced amino acid sequence of HbaR indicates that it is a member of the FNR-CRP superfamily of regulatory proteins. It is most closely related to transcriptional activators that are involved in regulating nitrate reduction. Previously, it has been shown that R. palustris has an FNR homologue, called AadR, that is also required for 4-HBA degradation. Our evidence indicates that AadR activates expression of hbaR in response to anaerobiosis and that HbaR, in turn, activates expression of 4-HBA degradation in response to 4-HBA as an effector molecule.

4-hydroxybenzoyl coenzyme A reductase (dehydroxylating) is required for anaerobic degradation of 4-hydroxybenzoate by Rhodopseudomonas palustris and shares features with molybdenum-containing hydroxylases

The anaerobic degradation of 4-hydroxybenzoate is initiated by the formation of 4-hydroxybenzoyl coenzyme A, with the next step proposed to be a dehydroxylation to benzoyl coenzyme A, the starting compound for a central pathway of aromatic compound ring reduction and cleavage. Three open reading frames, divergently transcribed from the 4-hydroxybenzoate coenzyme A ligase gene, hbaA, were identified and sequenced from the phototrophic bacterium Rhodopseudomonas palustris. These genes, named hbaBCD, specify polypeptides of 17.5, 82.6, and 34.5 kDa, respectively. The deduced amino acid sequences show considerable similarities to a group of hydroxylating enzymes involved in CO, xanthine, and nicotine metabolism that have conserved binding sites for [2Fe-2S] clusters and a molybdenum cofactor. Cassette disruption of the hbaB gene yielded a mutant that was unable to grow anaerobically on 4-hydroxybenzoate but grew normally on benzoate. The hbaB mutant cells did not accumulate [14C]benzoyl coenzyme A during short-term uptake of [14C]4-hydroxybenzoate, but benzoyl coenzyme A was the major radioactive metabolite formed by the wild type. In addition, crude extracts of the mutant failed to convert 4-hydroxybenzoyl coenzyme A to benzoyl coenzyme A. This evidence indicates that the hbaBCD genes encode the subunits of a 4-hydroxybenzoyl coenzyme A reductase (dehydroxylating). The sizes of the specified polypeptides are similar to those reported for 4-hydroxybenzoyl coenzyme A reductase isolated from the denitrifying bacterium Thauera aromatica. The amino acid consensus sequence for a molybdenum cofactor binding site is in HbaC. This cofactor appears to be an essential component because anaerobic growth of R. palustris on 4-hydroxybenzoate, but not on benzoate, was retarded unless 0.1 microM molybdate was added to the medium. Neither tungstate nor vanadate replaced molybdate, and tungstate competitively inhibited growth stimulation by molybdate.

Modeling the quinone-B binding site of the photosystem-II reaction center using notions of complementarity and contact-surface between atoms

Functional identity and significant similarities in cofactors and sequence exist between the L and M reaction center proteins of the photosynthetic bacteria and the D1 and D2 photosystem-II reaction center proteins of cyanobacteria, algae, and plants. A model of the quinone (QB) binding site of the D1 protein is presented based upon the resolved structure of the QB binding pocket of the L subunit, and introducing novel quantitative notions of complementarity and contact surface between atoms. This model, built without using traditional methods of molecular mechanics and restricted to residues in direct contact with QB, accounts for the experimentally derived functional state of mutants of the D1 protein in the region of QB. It predicts the binding of both the classical and phenol-type PSII herbicides and rationalizes the relative levels of tolerance of mutant phenotypes.

Structural and functional consequences of a Glu L212-->Lys mutation in the QB binding site of the photosynthetic reaction center of Rhodopseudomonas viridis

The properties of the quinone acceptor complex in the photosynthetic reaction center of the atrazine-resistant Rhodopseudomonas viridis mutant A2 (Glu L212-->Lys) were studied by EPR spectroscopy and by photoelectric measurements. The EPR signal attributed to the semiquinone-iron (QB-Fe2+) was significantly different from wild type and resembled that found in PS II. Essentially normal oscillations of QB-Fe2+ were observed upon flash illumination. The kinetics of the first and the second electron transfer from QA to QB were characterized by a photoelectric double-flash method. Compared to wild type, the rate of the first electron transfer in the large majority of reaction centers was decreased drastically from k1 = (18 microseconds)-1 in the wild type to (70 ms)-1 in the mutant, whereas the second electron transfer was only slightly slowed down with a rate of k2 = (260 microseconds)-1 compared to (65 microseconds)-1 in wild type (pH 7). When the pH was raised above 10, in a major fraction of the reaction centers a fast kinetics of the first electron transfer, like that in wild type, reappeared. The experimental results are interpreted as an effect of the positive charge on the lysine causing a significant structural change of the QB binding pocket and a strongly diminished affinity for ubiquinone. The slow QA(-)-->QB electron transfer kinetics are thus attributed to ubiquinone binding, which is rate limiting. The possible role of the residue Glu L212, which is conserved in all purple bacteria, in electron and proton transfer to QB is discussed.

Evidence that serine L223 is involved in the proton transfer pathway to QB in the photosynthetic reaction center of Rhodopseudomonas viridis

In the reaction center of purple photosynthetic bacteria, the reducing equivalents produced by primary charge separation are exported via an ubiquinone molecule working as a two-electron shuttle. This loosely-bound quinone, called QB, accepts in successive flashes two electrons from the tightly bound primary quinone acceptor QA, along with two protons from the external medium. The surrounding protein plays an important role in stabilizing the semiquinone anion and in providing a pathway for protons from the cytoplasmic phase to QB. Herbicides of the triazine type compete with QB for the binding pocket and their binding is controlled by nearby amino acid residues. We have studied the kinetics of the first and second electron transfer from QA to QB in two herbicide-resistant mutants from Rhodopseudomonas viridis, T1 (ArgL217-->His,Ser L223-->Ala) and MAV5 (Arg L217-->His, Val L220-->Leu), in order to determine whether these residues are involved in proton transfer to the reduced QB. The main effect of the mutant T1 was a drastic (600-fold at pH 7) decrease in the rate of the second electron transfer to QB compared to the wild type. In contrast, the rate of the second electron transfer in the mutant MAV5 was decreased only slightly (10-fold) in the pH range from 7 to 11. We attribute the inhibition of the second electron transfer in the Ser L223-->Ala mutation to an essential role of Ser L223 in the donation of the first proton to the reduced QB.(ABSTRACT TRUNCATED AT 250 WORDS)

Herbicide binding in the bacterial photosynthetic reaction center

The ureas and phenolics are two major classes of herbicides that act on Photosystem II (PSII) and are normally inactive in the photosynthetic reaction centers of purple bacteria. However, the triazine-resistant mutant T4 from Rhodopseudomonas (Rps.) viridis, which has the tyrosine residue at position 222 on the L subunit substituted for phenylalanine (TyrL222Phe), is sensitive to both ureas and phenolics. Since for the first time structural data on urea binding are available, T4 is a particularly interesting model for the herbicide-binding site of PSII.

Study of QB- stabilization in herbicide-resistant mutants from the purple bacterium Rhodopseudomonas viridis

The pH dependences of the rate constants of P+QB- (kBP) and P+QA- (kAP) charge recombination decays have been studied by flash-induced absorbance change technique, in chromatophores of three herbicide-resistant mutants from Rhodopseudomonas (Rps.) viridis, and compared to the wild type. P, QA, and QB are the primary electron donor and the primary and the secondary quinone acceptors, respectively. The triazine resistant mutants T1 (Arg L217----His and Ser L223----Ala), T3 (Phe L216----Ser and Val M263----Phe), and T4 (Tyr L222----Phe), all mutated in the QB binding pocket of the reaction center, have previously been characterized (Sinning, I., Michel, H., Mathis, P., & Rutherford, A. W. (1989) Biochemistry 28, 5544-5553). The pH dependence curves of kBP in T4 and the wild type are very close. This confirms that the sensitivity toward DCMU of T4 is mainly due to a structural rearrangement in the QB pocket rather than to a change in the charge distribution in this part of the protein. In T3, a 6-fold increase of kAP is observed (kAP = 4200 +/- 300 s-1 at pH 8) compared to that of the wild type (kAP = 720 +/- 50 s-1 at pH 8). We propose that the Val M263----Phe mutation induces a free energy decrease between P+QA- and P+I- (delta G zero IA) (I is the primary electron acceptor) of about 49 meV. The very different pH dependence of kAP in T3 suggests a substantial change in the QA pocket. The 2.5 times increase of kAP above pH 9.5 in the wild type is no longer detected in T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of Rhodobacter capsulatus mutants defective in oxygen regulation of the puf operon

cis-acting mutations that affect regulation of the Rhodobacter capsulatus puf operon by oxygen were isolated by placing the mutagenized puf regulatory region 5' to a promoterless Tn5 neo gene, which encodes resistance to kanamycin (Kmr). R. capsulatus mutants that failed to show wild-type repression of KMr by oxygen were selected and analyzed. Four independent clones contained point mutations, three of which were identical, in a region of dyad symmetry located between puf operon nucleotide positions 177 and 207, approximately 45 base pairs 5' to the site of initiation of puf transcripts. The phenotypic effects of the aerobically selected mutations were duplicated by single and double point mutations introduced site specifically into the region of dyad symmetry by oligonucleotide-directed mutagenesis. Determinations of the bacterial 50% lethal dose of kanamycin, of aminoglycoside phosphotransferase activity in cell sonicates, and of neo-specific mRNA confirmed the diminished responsiveness of the mutants to oxygen and consequently implicated the mutated region in O2-mediated transcriptional regulation.

Sequence analysis of four atrazine-resistant mutants from Rhodopseudomonas viridis

Four atrazine-resistant mutants from the purple bacterium Rhodopseudomonas viridis were isolated. Sequence analysis revealed three different mutant strains carrying mutations in the herbicide-binding pocket: i) MAV 2: L212-Glu----Lys, ii) MAV 3: L216-Phe----Ser and iii) MAV 4 = MAV 5: L217-Arg----His, L220-Val----Leu. Except MAV 3 all Rps. viridis mutants are different from those selected by their resistance towards the closely related triazine terbutryn.

Comparison of the contribution from different energy-linked reactions to the function of a membrane potential in photosynthetic bacteria

The steady-state membrane potentials generated by light, PP(i), ATP or the reverse transhydrogenase reaction were studied in chromatophores from two different phototrophic bacteria, Rhodospirillum rubrum and Rhodopseudomonas viridis. The membrane potentials generated by the different energy-linked reactions were evaluated by a tetraphenylboron(TPB(-)) ion-selective electrode. The generated by light was estimated to be 110 mV and 50 mV in R. rubrum and Rps. viridis chromatophores, respectively. In the dark, PP (i), ATP and reversed transhydrogenase generated membrane potentials in R. rubrum and Rps. viridis chromatophores 50, 60 and 35 mV, and 14, 35 and 25 mV,respectively. The effect of magnesium ion on the membrane potential generated by different energy-linked reactions was also studied. The induced by different energy-generating reactions in R. rubrum and Rps. viridis chromatophores and the possible relationship to the chromatophore structures are discussed.

Mutations conferring resistance to quinol oxidation (Qz) inhibitors of the cyt bc1 complex of Rhodobacter capsulatus

Several spontaneous mutants of the photosynthetic bacterium Rhodobacter capsulatus resistant to myxothiazol, stigmatellin and mucidin--inhibitors of the ubiquinol: cytochrome c oxidoreductase (cyt bc1 complex)--were isolated. They were grouped into eight different classes based on their genetic location, growth properties and inhibitor cross-resistance. The petABC (fbcFBC) cluster that encodes the structural genes for the Rieske FeS protein, cyt b and cyt c1 subunits of the cyt bc1 complex was cloned out of the representative isolates and the molecular basis of inhibitor-resistance was determined by DNA sequencing. These data indicated that while one group of mutations was located outside the petABC(fbcFBC) cluster, the remainder were single base pair changes in codons corresponding to phylogenetically conserved amino acid residues of cyt b. Of these substitutions, F144S conferred resistance to myxothiazol, T163A and V333A to stigmatellin, L106P and G152S to myxothiazol + mucidin and M140I and F144L to myxothiazol + stigmatellin. In addition, a mutation (aer126) which specifically impairs the quinol oxidase (Qz) activity of the cyt bc1 complex of a non-photosynthetic mutant (R126) was identified to be a glycine to an aspartic acid replacement at position 158 of cyt b. Six of these mutations were found between amino acid residues 140 and 163, in a region linking the putative third and fourth transmembrane helices of cyt b. The non-random clustering of several inhibitor-resistance mutations around the non-functional aer126 mutation suggests that this region may be involved in the formation of the Qz inhibitor binding/quinol oxidation domain(s) of the cyt bc1 complex. Of the two remaining mutations, the V333A replacement conferred resistance to stigmatellin exclusively and was located in another region toward the C terminus of cyt b. The L106P substitution, on the other hand, was situated in the transmembrane helix II that carries two conserved histidine residues (positions 97 and 111 in R. capsulatus) considered to be the axial ligands for the heme groups of cyt b. The structural and functional roles of the amino acid residues involved in the acquisition of Qz inhibitor resistance are discussed in terms of the primary structure of cyt b and in relation to the natural inhibitor-resistance of various phylogenetically related cyt bc/bf complexes.

Characterization of four herbicide-resistant mutants of Rhodopseudomonas viridis by genetic analysis, electron paramagnetic resonance, and optical spectroscopy

Herbicides of the triazine class block electron transfer in the photosynthetic reaction centers of purple bacteria and PSII of higher plants. They are thought to act by competing with one of the electron acceptors, the secondary quinone, QB, for its binding site. Several mutants of the purple bacterium Rhodopseudomonas viridis resistant to terbutryn [2-(methylthio)-4-(ethylamino)-6-(tert-butylamino)-s-triazine] have been isolated by their ability to grow photosynthetically in the presence of the herbicide. Sequence analysis of the genes coding for the L and M subunits of the reaction center showed that four different mutants were obtained, two of them being double mutated: T1 (SerL223----Ala and ArgL217----His), T3 (PheL216----Ser and ValM263----Phe), T4 (TyrL222----Phe), and T6 (PheL216----Ser). The residues L223 and L216 are involved in binding of QB, whereas L217 and L222 are not. M263 is part of the binding pocket of the primary quinone, QA. The affinity of the reaction centers for terbutryn and the electron transfer inhibitor o-phenanthroline, determined via the biphasic charge recombination after one flash, is decreased for all mutants. The affinity for ubiquinone 9 is also decreased, except in T1. Characterization by EPR spectroscopy showed that the QB.-Fe2+ signal of T4, having a g = 1.93 peak, is different from the signals obtained with the wild type and the other mutants but very similar to those of Rhodospirillum rubrum and PSII. The results obtained by the combination of these different techniques are discussed with respect to the three-dimensional structure of the wild type and the mode of binding of ubiquinone, terbutryn, and o-phenanthroline as determined by X-ray structure analysis.

Microaerophilic growth and induction of the photosynthetic reaction center in Rhodopseudomonas viridis

Rhodopseudomonas viridis was grown in liquid culture at 30 degrees C anaerobically in light (generation time, 13 h) and under microaerophilic growth conditions in the dark (generation time, 24 h). The bacterium could be cloned at the same temperature anaerobically in light (1 week) and aerobically in the dark (3 to 4 weeks) if oxygen was limited to 0.1%. Oxygen could not be replaced by dimethyl sulfoxide, potassium nitrate, or sodium nitrite as a terminal electron acceptor. No growth was observed anaerobically in darkness or in the light when air was present. A variety of additional carbon sources were used to supplement the standard succinate medium, but enhanced stationary-phase cell density was observed only with glucose. Conditions for induction of the photosynthetic reaction center upon the change from microaerophilic to phototrophic growth conditions were investigated and optimized for a mutant functionally defective in phototrophic growth. R. viridis consumed about 20-fold its cell volume of oxygen per hour during respiration. The MICs of ampicillin, kanamycin, streptomycin, tetracycline, 1-methyl-3-nitro-1-nitrosoguanidine, and terbutryn were determined.

Adaptive response to simple alkylating agents in the phototrophic bacteria Rhodobacter capsulatus and R.sphaeroides

The presence of an adaptive response to low doses of alkylating chemicals in the phototrophic bacteria Rhodobacter sphaeroides and R.capsulatus has been studied. Results obtained show that both strains display this repair response against the challenge doses of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), when they are pretreated with low doses of this compound for 120 min. The adaptive response of both R.sphaeroides and R.capsulatus induced an increase of cell survival and a decrease of mutagenesis in the MNNG-pretreated cells. Furthermore, the MNNG-induced adaptive repair also gives protection to diethylsulphate and ethylmethanesulphonate in both phototrophic bacteria. Finally, the MNNG-promoted adaptive response is sensitive to inhibitors of protein synthesis such as chloramphenicol, indicating that this DNA repair mechanism needs protein synthesis in R.sphaeroides and R.capsulatus, in a way similar to that which occurs in Escherichia coli.

Effect of uncoupler on assembly pathway for pigment-binding protein of bacterial photosynthetic membranes

The uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) was used to investigate membrane protein assembly in the phototrophic bacterium Rhodobacter capsulatus. As found for Escherichia coli (T. Date, G. Zwizinsky, S. Ludmerer, and W. Wickner, Proc. Natl. Acad. Sci. 77:827-831, 1980) and mitochondrial proteins (N. Nelson and G. Schatz, Proc. Natl. Acad. Sci. USA 76:4365-4369, 1979), assembly across the bacterial photosynthetic membranes was sensitive to CCCP. At uncoupler concentrations which were sufficient to block the export of the periplasmic cytochrome c2 and an outer membrane protein, the integration of pigment-binding protein into the photosynthetic apparatus was abolished. The unassembled protein was detected on the inner surface of the intracytoplasmic membrane. After inactivation of CCCP, accumulated protein continued insertion into the membrane. The data suggest that after binding to the cytoplasmic face of the membrane, translocation of protein into a transmembrane orientation takes place, which is a prerequisite for the formation of a functional pigment-protein complex.

Development of a gene cloning system for the hydrogen-producing marine photosynthetic bacterium Rhodopseudomonas sp

Seventy-six strains of marine photosynthetic bacteria were analyzed by agarose gel electrophoresis for plasmid DNA content. Among these strains, 12 carried two to four different plasmids with sizes ranging from 3.1 to 11.0 megadaltons. The marine photosynthetic bacterium Rhodopseudomonas sp. NKPB002106 had two plasmids, pRD06S and pRD06L. The smaller plasmid, pRD06S, had a molecular weight of 3.8 megadaltons and was cut at a single site by restriction endonucleases SalI, SmaI, PstI, XhoI, and BglII. Moreover, the marine photosynthetic bacterium Rhodopseudomonas sp. NKPB002106 containing plasmid pRD06 had a satisfactory growth rate (doubling time, 7.5 h), a hydrogen-producing rate of 0.96 mumol/mg (dry weight) of cells per h, and nitrogen fixation capability. Plasmid pRD06S, however, had neither drug resistance nor heavy-metal resistance, and its copy number was less than 10. Therefore, a recombinant plasmid consisting of pRD06S and Escherichia coli cloning vector pUC13 was constructed and cloned in E. coli. The recombinant plasmid was transformed into Rhodopseudomonas sp. NKPB002106. As a result, Rhodopseudomonas sp. NKPB002106 developed ampicillin resistance. Thus, a shuttle vector for gene transfer was constructed for marine photosynthetic bacteria.

Primary donor recovery kinetics in reaction centers from Rhodopseudomonas viridis. The influence of ferricyanide as a rapid oxidant of the acceptor quinones

In reaction centers from Rhodopseudomonas viridis that contain a single quinone, the decay of the photo-oxidized primary donor, P+, was found to be biphasic when the bound, donor cytochromes were chemically oxidized by ferricyanide. The ratio of the two phases was dependent on pH with an apparent pK of 7.6. A fast phase, which dominated at high pH (t1/2 = 1 ms at pH 9.5), corresponded to the expected charge recombination of P+ and the primary acceptor QA-. A much slower phase dominated at low pH and was shown to arise from a slow reduction of P+ by ferrocyanide in reaction centers where QA- has been rapidly oxidized by ferricyanide. The rate of QA- oxidation was linear with respect to ferricyanide activity and was strongly pH-dependent. The second-order rate constant, corrected for the activity coefficient of ferricyanide, approached a maximum of 2 X 10(8) M-1 X s-1 at low pH, but decreased steadily as the pH was raised above a pK of 5.8, indicating that a protonated state of the reaction center was involved. The slow reduction of P+ by ferrocyanide was also second-order, with a maximum rate constant at low pH of 8 X 10(5) M-1 X s-1 corrected for the activity coefficient of ferrocyanide. This rate also decreased at higher pH, with a pK of 7.4, indicating that ferrocyanide also was most reactive with a protonated form of the reaction center. The oxidation of QA- by ferricyanide was unaffected by the presence of o-phenanthroline, implying that access to QA- was not via the QB-binding site. In reaction centers supplemented with ubiquinone, oxidation of reduced secondary quinone, QB-, by ferricyanide was observed but was substantially slower than that for QA-. It is suggested that Q-B may be oxidized via QA so that the rate is modulated by the equilibrium constant for QA-QB in equilibrium with QAQB-.

Nitrous oxide reduction by members of the family Rhodospirillaceae and the nitrous oxide reductase of Rhodopseudomonas capsulata

After growth in the absence of nitrogenous oxides under anaerobic phototrophic conditions, several strains of Rhodopseudomonas capsulata were shown to possess a nitrous oxide reductase activity. The enzyme responsible for this activity had a periplasmic location and resembled a nitrous oxide reductase purified from Pseudomonas perfectomarinus. Electron flow to nitrous oxide reductase was coupled to generation of a membrane potential and inhibited by rotenone but not antimycin. It is suggested that electron flow to nitrous oxide reductase branches at the level of ubiquinone from the previously characterized electron transfer components of R. capsulata. This pathway of electron transport could include cytochrome c', a component hitherto without a recognized function. R. capsulata grew under dark anaerobic conditions in the presence of malate as carbon source and nitrous oxide as electron acceptor. This confirms that nitrous oxide respiration is linked to ATP synthesis. Phototrophically and anaerobically grown cultures of nondenitrifying strains of Rhodopseudomonas sphaeroides, Rhodopseudomonas palustris, and Rhodospirillum rubrum also possessed nitrous oxide reductase activity.

Isolation of a recombination-deficient mutant of Rhodopseudomonas capsulata

To facilitate genetic analysis in the purple photosynthetic bacterium Rhodopseudomonas capsulata, a recombination-deficient derivative was sought. A UV irradiation-sensitive mutant (FG106F) was isolated after mutagenesis, and two procedures were used to determine the recombinational capacity of the mutant. First, recombinants were not detected after transduction of this derivative by the phage-like vector gene transfer agent. Second, an R-prime plasmid containing appropriately marked genes for photosynthesis was introduced by conjugation, and again no recombinants were observed. Additional phenotypes displayed by the mutant that are characteristic of a defect in recombination were an increased sensitivity to DNA-damaging antibiotics and a tendency to filament.

Depression of the synthesis of the intermediate and large forms of ribulose-1,5-bisphosphate carboxylase/oxygenase in Rhodopseudomonas capsulata

Rhodopseudomonas capsulata produces both an intermediate (I) and a large (L) form of ribulose-1,5-bisphosphate carboxylase/oxygenase. Both forms are derepressed under CO2-limiting conditions. The L-form of the enzyme is completely repressed when the culture is grown either photoautotrophically or photoheterotrophically with malate as the electron donor. The L-form is derepressed in the late logarithmic phase of growth when cells are grown photoheterotrophically with butyrate as the electron donor and the NaHCO3 supplement is 0.01%. The level of the I-form is increased about fivefold under latter growth conditions when compared to malate-grown cells. Analytical ultracentrifugation revealed the molecular masses of the I- and L-forms to be 300,000 and 542,000, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the I-form to be composed of only one type subunit with a molecular weight of 64,000. The L-form possessed both large and small subunits with molecular weights of 58,000 and 10,000.

Electron flow to dimethylsulphoxide or trimethylamine-N-oxide generates a membrane potential in Rhodopseudomonas capsulata

Under dark and essentially anaerobic conditions electron flow to either dimethylsulphoxide or trimethylamine-N-oxide in cells of Rhodopseudomonas capsulata has been shown to generate a membrane potential. This conclusion is based on the observation of a red shift in the carotenoid absorption band which is a well characterised indicator of membrane potential in this bacterium. The magnitude of the dimethylsulphoxide- or trimethylamine-N-oxide-dependent membrane potential was reduced either by a protonophore uncoupler of oxidative phosphorylation or synergistically by a combination of a protonophore plus rotenone, an inhibitor of electron flow from NADH dehydrogenase. These findings, together with the observation that venturicidin, an inhibitor of the proton translocating ATPase, did not reduce the membrane potential, show that electron flow to dimethylsulphoxide or trimethylamine-N-oxide is coupled to proton translocation. Thus contrary to some previous proposals dark and anaerobic growth of Rps. capsulata in the presence of dimethylsulphoxide or trimethylamine-N-oxide cannot be regarded as purely fermentative.

Transcriptional regulation of several genes for bacteriochlorophyll biosynthesis in Rhodopseudomonas capsulata in response to oxygen

Although it has been shown that bacteriochlorophyll synthesis in Rhodopseudomonas capsulata is repressed by oxygen and high light intensity, few details of regulation by these environmental factors are known, primarily owing to a lack of assays for the biosynthetic enzymes. We have examined regulation at the transcriptional level by isolating and studying fusions between the Mu d1(Apr lac) phage and various bch genes. In these strains, the lacZ gene of the phage is under the control of bch gene promoters. We have found that atmospheric oxygen tension (20% O2) reduces the expression of these fusions at least twofold compared with low oxygen tension (2% O2). Therefore, transcription of the bchA, bchB, bchC, bchG, and bchH genes is regulated in response to oxygen.

Oxygen-induced inhibition of light-dependent uptake of tetraphenylphosphonium ions as a probe of a direct interaction between photosynthetic and respiratory components in cells of Rhodopseudomonas capsulata

Light-generated and oxygen-dependent membrane potentials by heterotrophycally grown cells of Rhodopseudomonas capsulata have been investigated by using a tetraphenylphosphonium ion-selective electrode. The results show that respiratory electron transport affects the magnitude of photogenerated membrane potential while photosynthesis seems to either inhibit or stimulate respiration in coupled or uncoupled cells, respectively. These observations have been considered as evidence that the intracytoplasmic membrane system of R. capsulata contain respiratory and photosynthetic apparatuses which are strictly intermingled.

Uncouplers can shuttle between localized energy-coupling sites during photophosphorylation by chromatophores of Rhodopseudomonas capsulata N22

Two models of the action of uncoupler molecules in inhibiting photophosphorylation in bacterial chromatophores are considered: either uncoupler molecules shuttle rapidly between energy-coupling sites, or uncoupler molecules that are bound to particular sites in the chromatophores for a time that is comparable with the turnover time of the photophosphorylation apparatus may uncouple by a co-operative "substoichiometric' mechanism. It is found that the titre of uncoupler necessary to cause complete uncoupling is lowered if the rate of photophosphorylation is initially decreased by partially restricting electron flow with an appropriate titre of antimycin A. This result indicates that uncoupler molecules shuttle rapidly between energy coupling in which the energized intermediate between electron transport and phosphorylation is delocalized over the entire chromatophore membrane and those in which it is not. If the rate of photophosphorylation is partially restricted with the covalent H+-translocating ATP synthase inhibitor dicyclohexylcarbodi-imide, the titre of uncoupler necessary to effect complete inhibition of photophosphorylation is also decreased relative to that in which the covalent H+-ATP synthase inhibitor is absent. This important result appears to be inconsistent with models of electron-transport phosphorylation in which the "energized state' of the chromatophore membrane that is set up by electron transport and utilized in photophosphorylation is delocalized over the entire chromatophore membrane.

Alterations in the phospholipid composition of Rhodopseudomonas sphaeroides and other bacteria induced by Tris

Alterations in the phospholipid head group composition of most strains of Rhodopseudomonas sphaeroides, as well as Rhodopseudomonas capsulata and Paracoccus denitrificans, occurred when cells were grown in medium supplemented with Tris. Growth of R. sphaeroides M29-5 in Tris-supplemented medium resulted in the accumulation of N-acylphosphatidylserine (NAPS) to as much as 40% of the total whole-cell phospholipid, whereas NAPS represented approximately 28 an 33% of the total phospholipid when R. capsulata and P. denitrificans respectively, were grown in medium containing 20 mM Tris. The accumulation of NAPS occurred primarily at the expense of phosphatidylethanolamine in both whole cells and isolated membranes of R. sphaeroides and had no detectable effect on cell growth under either chemoheterotrophic or photoheterotrophic conditions. Yeast extract (0.1%) and Casamino Acids (1.0%) were found to be antagonistic to the Tris-induced (20 mM) alteration in the phospholipid composition of R. sphaeroides. The wild-type strains R. sphaeroides 2.4.1 and RS2 showed no alteration in their phospholipid composition when they were grown in medium supplemented with Tris. In all strains of Rhodospirillaceae tested, as well as in P. denitrificans, NAPS represented between 1.0 and 2.0% of the total phospholipid when cells were grown in the absence of Tris. [32P]orthophosphoric acid entered NAPS rapidly in strains of R. sphaeroides that do (strain M29-5) and do not (strain 2.4.1) accumulate this phospholipid in response to Tris. Our data indicate that the phospholipid head group composition of many Rhodospirillaceae strains, as well as P. denitrificans, is easily manipulated; thus, these bacteria may provide good model systems for studying the effects of these modifications on membrane structure and function in a relatively unperturbed physiological system.

On the extent of localization of the energized membrane state in chromatophores from Rhodopseudomonas capsulata N22

1. The principle of the double-inhibitor titration method for assessing competing models of electron transport phosphorylation is expounded. 2. This principle is applied to photophosphorylation by chromatophores from Rhodopseudomonas capsulata N22. 3. It is found that, in contrast to the predictions of the chemiosmotic coupling model, free energy transfer is confined to individual electron transport chain and ATP synthase complexes. 4. This conclusion is not weakened by arguments concerning, the degree of uncoupling in the native chromatophore preparation or the relative number of electron transport chain and ATP synthase complexes present. 5. Photophosphorylation is completely inhibited by the uncoupler SF 6847 at a concentration corresponding to 0.31 molecules per electron transport chain. 6. The apparent paradox is solved by the proposal, consistent with the available evidence on the mode of action of uncouplers, that uncoupler binding causes a co-operative conformation transition in the chromatophore membrane, which leads to uncoupling and which is not present in the absence of uncoupler.

Regulation of nitrogenase A and R concentrations in Rhodopseudomonas capsulata by glutamine synthetase

Nitrogen-starved purple non-sulphur bacteria have an active unregulated form of nitrogenase (nitrogenase A); however, the nitrogenase of a glutamine synthetase-negative mutant of Rhodopseudomonas capsulata, when nitrogen-starved, was predominantly inactive and required activation by Mn2+ and activating-factor protein. This regulatory form of nitrogenase has been called nitrogenase R. Treatment of wild-type cells (containing nitrogenase A) with methionine sulphoximine, an inhibitor of glutamine synthetase, converted the enzyme into nitrogenase R. Glutamine synthetase thus appears to control the intracellular concentrations of nitrogenase A and R and in this way regulates nitrogenase activity in the photosynthetic bacterium.

The effect of nalidixic acid on the cell cycle of synchronous Rhodopseudomonas palustris cultures

The influence of the DNA synthesis inhibitor, nalidixic acid, on the properties of synchronous cultures of selected Rhodopseudomonas palustris swarmer cells was examined. There was little alteration in the changes in morphology, extinction, volume distribution and leucine incorporation up to bud development, and photosynthetic membrane lamellae were still synthesized de novo in the bud. However, there was no subsequent division, or flagellum or holdfast synthesis. Instead cells elongated by continued outgrowth of the abortive bud. Since DNA synthesis was also inhibited, this suggested a dependence of cell division, and flagellum and holdfast synthesis, on the completion of chromosome replication. By addition or removal of nalidixic acid at various times in the cell cycle, periods were demonstrated when the organism was insensitive to the antibiotic indicating that there was a pre-synthetic and post-synthetic gap in the pattern of DNA synthesis in R. palustris swarmers.

Characterization of Rhodopseudomonas capsulata

Thirty-three strains of Rhodopseudomonas capsulata have been studied in order to develop a more comprehensive characterization of the species. On the basis of morphological, nutritional, physiological and other properties, the characteristics of an "ideal biotype" have been defined, which can be used to distinguish Rps. capsulata from similar purple bacteria. In this connection, two properties of Rps. capsulata are of particular note: a) sensitivity to penicillin G is 10(3)-10(5) times greater than that shown by closely related species, and b) all strains examined are susceptible to lysis by one or more strains of host species-specific virulent bacteriophages. It appears that members of the species Rps. capsulata form a stringent taxonomic grouping.