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Bacteriophytochrome photoreceptors (BphPs) and their cognate response regulators make up two-component signal transduction systems which direct bacteria to mount phenotypic responses to changes in environmental light quality. Most of these systems utilize single-domain response regulators to transduce signals through unknown pathways and mechanisms. Here we describe the photocycle and autophosphorylation kinetics of RtBphP1, a red light-regulated histidine kinase from the desert bacterium Ramlibacter tataouinensis. RtBphP1 undergoes red to far-red photoconversion with rapid thermal reversion to the dark state. RtBphP1 is autophosphorylated in the dark; this activity is inhibited under red light. The RtBphP1 cognate response regulator, the R. tataouinensis bacteriophytochrome response regulator (RtBRR), and a homolog, AtBRR from Agrobacterium tumefaciens, crystallize unexpectedly as arm-in-arm dimers, reliant on a conserved hydrophobic motif, hFWAhL (where h is a hydrophobic M, V, L, or I residue). RtBRR and AtBRR dimerize distinctly from four structurally characterized phytochrome response regulators found in photosynthetic organisms and from all other receiver domain homodimers in the Protein Data Bank. A unique cacodylate-zinc-histidine tag metal organic framework yielded single-wavelength anomalous diffraction phases and may be of general interest. Examination of the effect of the BRR stoichiometry on signal transduction showed that phosphorylated RtBRR is accumulated more efficiently than the engineered monomeric RtBRR (RtBRRmon) in phosphotransfer reactions. Thus, we conclude that arm-in-arm dimers are a relevant signaling intermediate in this class of two-component regulatory systems. [ABSTRACT FROM AUTHOR]

Microbial sulfide oxidation in aquatic environments is an important ecosystem process, as sulfide is potently toxic to aerobic organisms. Sulfide oxidation in anoxic waters can prevent the efflux of sulfide to aerobic water masses, thus mitigating toxicity. The contribution of phototrophic sulfide-oxidizing bacteria to anaerobic sulfide oxidation in the Chesapeake Bay and the redox chemistry of the stratified water column were investigated in the summers of 2011 to 2014. In 2011 and 2013, phototrophic sulfide-oxidizing bacteria closely related to Prosthecochloris species of the phylum Chlorobi were cultivated from waters sampled at and below the oxic-anoxic interface, where measured light penetration was sufficient to support populations of low-light-adapted photosynthetic bacteria. In 2012, 2013, and 2014, light-dependent sulfide loss was observed in freshly collected water column samples. In these samples, extremely low light levels caused 2- to 10-fold increases in the sulfide uptake rate over the sulfide uptake rate under dark conditions. An enrichment, CB11, dominated by Prosthecochloris species, oxidized sulfide with a Ks value of 11 μM and a Vmax value of 51 μM min-1 (mg protein-1). Using these kinetic values with in situ sulfide concentrations and light fluxes, we calculated that a small population of Chlorobi similar to those in enrichment CB11 can account for the observed anaerobic light-dependent sulfide consumption activity in natural water samples. We conclude that Chlorobi play a far larger role in the Chesapeake Bay than currently appreciated. This result has potential implications for coastal anoxic waters and expanding oxygen-minimum zones as they begin to impinge on the photic zone. [ABSTRACT FROM AUTHOR]

The purple sulfur bacterium Allochromatium vinosum DSM 180T is one of the best-studied sulfur-oxidizing anoxygenic phototrophic bacteria, and it has been developed into a model organism for laboratory-based studies of oxidative sulfur metabolism. Here, we took advantage of the organism's high metabolic versatility and performed whole-genome transcriptional profiling to investigate the response of A. vinosum cells upon exposure to sulfide, thiosulfate, elemental sulfur, or sulfite compared to photoorganoheterotrophic growth on malate. Differential expression of 1,178 genes was observed, corresponding to 30% of the A. vinosum genome. Relative transcription of 551 genes increased significantly during growth on one of the different sulfur sources, while the relative transcript abundance of 627 genes decreased. A significant number of genes that revealed strongly enhanced relative transcription levels have documented sulfur metabolism-related functions. Among these are the dsr genes, including dsrAB for dissimilatory sulfite reductase, and the sgp genes for the proteins of the sulfur globule envelope, thus confirming former results. In addition, we identified new genes encoding proteins with appropriate subcellular localization and properties to participate in oxidative dissimilatory sulfur metabolism. Those four genes for hypothetical proteins that exhibited the strongest increases of mRNA levels on sulfide and elemental sulfur, respectively, were chosen for inactivation and phenotypic analyses of the respective mutant strains. This approach verified the importance of the encoded proteins for sulfur globule formation during the oxidation of sulfide and thiosulfate and thereby also documented the suitability of comparative transcriptomics for the identification of new sulfur-related genes in anoxygenic phototrophic sulfur bacteria. [ABSTRACT FROM AUTHOR]

Light is a ubiquitous environmental signal that many organisms sense and respond to by modulating their physiological responses accordingly. While this is an expected response among phototrophic microorganisms, the ability of chemotrophic prokaryotes to sense and react to light has become a puzzling and novel issue in bacterial physiology, particularly among bacterial pathogens. In this work, we show that the opportunistic pathogen Acinetobacter baumannii senses and responds to blue light. Motility and formation of biofilms and pellicles were observed only when bacterial cells were incubated in darkness. In contrast, the killing of Candida albicans filaments was enhanced when they were cocultured with bacteria under light. These bacterial responses depend on the expression of the A. baumannii ATCC 17978 A1S_2225 gene, which codes for an 18.6-kDa protein that contains an N-terminal blue-light-sensing-using flavin (BLUF) domain and lacks a detectable output domain(s). Spectral analyses of the purified recombinant protein showed its ability to sense light by a red shift upon illumination. Therefore, the A1S_2225 gene, which is present in several members of the Acinetobacter genus, was named blue-light-sensing A (blsA). Interestingly, temperature plays a role in the ability of A. baumannii to sense and respond to light via the BlsA photoreceptor protein. [ABSTRACT FROM AUTHOR]

Nitrogenase activity in Rhodospirillum rubrum and in some other photosynthetic bacteria is regulated in part by the availability of light. This regulation is through a posttranslational modification system that is itself regulated by PII homologs in the cell. PII is one of the most broadly distributed regulatory proteins in nature and directly or indirectly senses nitrogen and carbon signals in the cell. However, its possible role in responding to light availability remains unclear. Because PII binds ATP, we tested the hypothesis that removal of light would affect PII by changing intracellular ATP levels, and this in turn would affect the regulation of nitrogenase activity. This in vivo test involved a variety of different methods for the measurement of ATP, as well as the deliberate perturbation of intracellular ATP levels by chemical and genetic means. To our surprise, we found fairly normal levels of nitrogenase activity and posttranslational regulation of nitrogenase even under conditions of drastically reduced ATP levels. This indicates that low ATP levels have no more than a modest impact on the PII-mediated regulation of NifA activity and on the posttranslational regulation of nitrogenase activity. The relatively high nitrogenase activity also shows that the ATP-dependent electron flux from dinitrogenase reductase to dinitrogenase is also surprisingly insensitive to a depleted ATP level. These in vivo results disprove the simple model of ATP as the key energy signal to PII under these conditions. We currently suppose that the ratio of ADP/ATP might be the relevant signal, as suggested by a number of recent in vitro analyses. [ABSTRACT FROM AUTHOR]

In the facultatively phototrophic proteobacterium Rhodobacter sphaeroides, formation of the photosynthetic apparatus is oxygen dependent. When oxygen tension decreases, the response regulator PrrA of the global two-component PrrBA system is believed to directly activate transcription of the puf, puh, and puc operons, encoding structural proteins of the photosynthetic complexes, and to indirectly upregulate the photopigment biosynthesis genes bch and crt. Decreased oxygen also results in inactivation of the photosynthesis-specific repressor PpsR, bringing about derepression of the puc, bch, and crt operons. We uncovered a hierarchical relationship between these two regulatory systems, earlier thought to function independently. We also more accurately assessed the spectrum of gene targets of the PrrBA system. First, expression of the appA gene, encoding the PpsR antirepressor, is PrrA dependent, which establishes one level of hierarchical dominance of the PrrBA system over AppA-PpsR. Second, restoration of the appA transcript to the wild-type level is insufficient for rescuing phototrophic growth impairment of the prrA mutant, whereas inactivation of ppsR is sufficient. This suggests that in addition to controlling appA transcription, PrrA affects the activity of the AppA-PpsR system via an as yet unidentified mechanism(s). Third, PrrA directly activates several bch and crt genes, traditionally considered to be the PpsR targets. Therefore, in R. sphaeroides, the global PrrBA system regulates photosynthesis gene expression (i) by rigorous control over the photosynthesis-specific AppA-PpsR regulatory system and (ii) by extensive direct transcription activation of genes encoding structural proteins of photosynthetic complexes as well as genes encoding photopigment biosynthesis enzymes. [ABSTRACT FROM AUTHOR]

The cyclization of lycopene to {gamma}- or β-carotene is a major branch point in the biosynthesis of carotenoids in photosynthetic bacteria. Four families of carotenoid cyclases are known, and each family includes both mono- and dicyclases, which catalyze the formation of {gamma}- and β-carotene, respectively. Green sulfur bacteria (GSB) synthesize aromatic carotenoids, of which the most commonly occurring types are the monocyclic chlorobactene and the dicyclic isorenieratene. Recently, the cruA gene, encoding a conserved hypothetical protein found in the genomes of all GSB and some cyanobacteria, was identified as a lycopene cyclase. Further genomic analyses have found that all available fully sequenced genomes of GSB encode an ortholog of cruA. Additionally, the genomes of all isorenieratene-producing species of GSB encode a cruA paralog, now named cruB. The cruA gene from the chlorobactene-producing GSB species Chlorobaculum tepidum and both cruA and cruB from the brown-colored, isorenieratene-producing GSB species Chlorobium phaeobacteroides strain DSM 266T were heterologously expressed in lycopene- and neurosporene-producing strains of Escherichia coli, and the cruB gene of Chlorobium clathratiforme strain DSM 5477T was also heterologously expressed in C. tepidum by inserting the gene at the bchU locus. The results show that CruA is probably a lycopene monocyclase in all GSB and that CruB is a {gamma}-carotene cyclase in isorenieratene-producing species. Consequently, the branch point for the synthesis of mono- and dicyclic carotenoids in GSB seems to be the modification of {gamma}-carotene, rather than the cyclization of lycopene as occurs in cyanobacteria. [ABSTRACT FROM AUTHOR]

It is now well established that, for photosynthetic bacteria, the aerobic-to-microaerophilic transition activates the membrane-bound sensor kinase RegB, which subsequently phosphorylates the transcriptional activator RegA, thereby inducing elevated levels of intracellular photosynthetic membranes. The mechanism of RegB activation—in particular, the role of ubiquinone-10—is controversial at present. One problem here is that very limited quantitative in vivo data for the response of the ubiquinone redox state to different cultivation conditions exist. Here, we utilize Rhodospirillum rubrum to study the correlation of the quinone redox state to the expression level of photosynthetic membranes and determine an effective response function directly. Our results show that changes in the photosynthetic membrane levels between 50 and 95% of that maximally attainable are associated with only a twofold change in the ubiquinol/ubiquinone ratio and are not necessarily proportional to the total levels of either quinone or [NAD+ + NADH]. There is no correlation between the redox potentials of the quinone and pyridine nucleotide pools. Hill function analysis of the photosynthetic membrane induction in response to the quinone redox state suggests that the induction process is highly cooperative. Our results are probably generally applicable to quinone redox regulation in bacteria. [ABSTRACT FROM AUTHOR]

SenC, a Sco1 homolog found in the purple photosynthetic bacteria, has been implicated in affecting photosynthesis and respiratory gene expression, as well as assembly of cytochrome c oxidase. In this study, we show that SenC from Rhodobacter capsulatus is involved in the assembly of a fully functional cbb3-type cytochrome c oxidase, as revealed by decreased cytochrome c oxidase activity in a senC mutant. We also show that a putative copper-binding site in SenC is required for activity and that a SenC deletion phenotype can be rescued by the addition of exogenous copper to the growth medium. In addition, we demonstrate that a SenC mutation has an indirect effect on gene expression caused by a reduction in cytochrome c oxidase activity. A model is proposed whereby a reduction in cytochrome c oxidase activity impedes the flow of electrons through the respiratory pathway, thereby affecting the oxidation/reduction state of the ubiquinone pool, leading to alterations of photosystem and respiratory gene expression. [ABSTRACT FROM AUTHOR]

During growth on ethanolamine, Salmonella enterica synthesizes a multimolecular structure that mimics the carboxysome used by some photosynthetic bacteria to fix CO2. In S. enterica, this carboxysome-like structure (hereafter referred to as the ethanolamine metabolosome) is thought to contain the enzymatic machinery needed to metabolize ethanolamine into acetyl coenzyme A (acetyl-CoA). Analysis of the growth behavior of mutant strains of S. enterica lacking specific functions encoded by the 17-gene ethanolamine utilization (eut) operon established the minimal biochemical functions needed by this bacterium to use ethanolamine as a source of carbon and energy. The data obtained support the conclusion that the ethanolamine ammnonia-lyase (EAL) enzyme (encoded by the eutBC genes) and coenzyme B12 are necessary and sufficient to grow on ethanolamine. We propose that the EutD phosphotransacetylase and EutG alcohol dehydrogenase are important to maintain metabolic balance. Glutathione (GSH) had a strong positive effect that compensated for the lack of the EAL reactivase EutA protein under aerobic growth on ethanolamine. Neither GSH nor EutA was needed during growth on ethanolamine under reduced-oxygen conditions. GSH also stimulated growth of a strain lacking the acetaldehyde dehydrogenase (EutE) enzyme. The role of GSH in ethanolamine catabolism is complex and requires further investigation. Our data show that the ethanolamine metabolosome is not involved in the biochemistry of ethanolamine catabolism. We propose the metabolosome is needed to concentrate low levels of ethanolamine catabolic enzymes, to keep the level of toxic acetaldehyde low, to generate enough acetyl-CoA to support cell growth, and to maintain a pool of free CoA. [ABSTRACT FROM AUTHOR]

PpsR from the anoxygenic phototrophic bacterium Rhodobacter sphaeroides has been known as an oxygen- and light-dependent repressor of bacteriochiorophyll and carotenoid biosynthesis genes and puc operons involved in photosystem development. However, the putative PpsR-binding sites, TGTN12ACA, are also located upstream of numerous nonphotosystem genes, thus raising the possibility that the role of PpsR is broader. To characterize the PpsR regulon, transcriptome profiling was performed on the wild-type strain grown at high and low oxygen tensions, on the strain overproducing PpsR, and on the ppsR mutant. Transcriptome analysis showed that PpsR primarily regulates photosystem genes; the consensus PpsR binding sequence is TGTcN10gACA (lowercase letters indicate lesser conservation); the presence of two binding sites is required for repression in vivo. These findings explain why numerous single TGTN12ACA sequences are nonfunctional. In addition to photosystem genes, the hemC and hemE genes involved in the early steps of tetrapyrrole biosynthesis were identified as new direct targets of PpsR repression. Unexpectedly, PpsR was found to indirectly repress the puf and puhA operons encoding photosystem core proteins. The upstream regions of these operons contain no PpsR binding sites. Involvement in regulation of these operons suggests that PpsR functions as a master regulator of photosystem development. Upregulation of the puf and puhA operons that resulted from ppsR inactivation was sufficient to restore the ability to grow phototrophically to the prrA mutant. PrrA, the global redox-dependent activator, was previously considered indispensable for phototrophic growth. It is revealed that the PrrBA and AppA-PpsR systems, believed to work independently, in fact interact and coordinately regulate photosystem development. [ABSTRACT FROM AUTHOR]

The photochemical reaction center (RC) complex of Roseiflexus castenholzii, which belongs to the filamentous anoxygenic phototrophic bacteria (green filamentous bacteria) but lacks chlorosomes, was isolated and characterized. The genes coding for the subunits of the RC and the light-harvesting proteins were also cloned and sequenced. The RC complex was composed of L, M, and cytochrome subunits. The cytochrome subunit showed a molecular mass of approximately 35 kDa, contained hemes c, and functioned as the electron donor to the photo-oxidized special pair of bacteriochlorophylls in the RC. The RC complex appeared to contain three molecules of bacteriochlorophyll and three molecules of bacteriopheophytin, as in the RC preparation from Chioroflexus aura ntiacus. Phylogenetic trees based on the deduced amino acid sequences of the RC subunits suggested that R. castenholzii had diverged from C. aura ntiacus very early after the divergence of filamentous anoxygenic phototrophic bacteria from purple bacteria. Although R. castenholzii is phylogenetically related to C. aurantiacus, the arrangement of its puf genes, which code for the light-harvesting proteins and the RC subunits, was different from that in C. aurantiacus and similar to that in purple bacteria. The genes are found in the order pufB, -A, -L, -M, and -C, with the puJL and puJM genes forming one continuous open reading frame. Since the photosynthetic apparatus and genes of R. castenholzii have intermediate characteristics between those of purple bacteria and C. aurantiacus, it is likely that they retain many features of the common ancestor of purple bacteria and filamentous anoxygenic phototrophic bacteria. [ABSTRACT FROM AUTHOR]

The core of the photosynthetic apparatus of purple photosynthetic bacteria such as Rhodobacter capsulatus consists of a reaction center (RC) intimately associated with light-harvesting complex 1 (LH1) and the PufX polypeptide. The abundance of the RC and LH1 components was previously shown to depend on the product of the puhB gene (formerly known as orf214). We report here that disruption of puhB diminishes RC assembly, with an indirect effect on LH1 assembly, and reduces the amount of PufX. Under semiaerobic growth conditions, the core complex was present at a reduced level in puhB mutants. After transfer of semiaerobically grown cultures to photosynthetic (anaerobic illuminated) conditions, the RC/LH1 complex became only slightly more abundant, and the amount of PufX increased as cells began photosynthetic growth. We discovered that the photosynthetic growth of puhB disruption strains of R. capsulatus starts after a long lag period, which is due to physiological adaptation rather than secondary mutations. Using a hybrid protein expression system, we determined that the three predicted transmembrane segments of PuhB are capable of spanning a cell membrane and that the second transmembrane segment could mediate self-association of PuhB. We discuss the possible function of PuhB as a dimeric RC assembly factor. [ABSTRACT FROM AUTHOR]

In Rhodobacter capsulatus, genes encoding enzymes of the Calvin-Benson-Bassham reductive pentose phosphate pathway are located in the cbbI and cbbII operons. Each operon contains a divergently transcribed LysR-type transcriptional activator (CbbRI and CbbRII) that regulates the expression of its cognate cbb promoter in response to an as yet unidentified effector molecule(s). Both CbbRI and CbbRII were purified, and the ability of a variety of potential effector molecules to induce changes in their DNA binding properties at their target promoters was assessed. The responses of CbbRI and CbbRII to potential effectors were not identical. In gel mobility shift assays, the affinity of both CbbRI and CbbRII for their target promoters was enhanced in the presence of ribulose-1,5-bisphosphate (RuBP), phosphoenolpyruvate, 3-phosphoglycerate, 2-phosphoglycolate. ATP, 2-phosphoglycerate, and KH2PO4 were found to enhance only CbbRI binding, while fructose-1,6-bisphosphate enhanced the binding of only CbbRII. The DNase I footprint of CbbRI was reduced in the presence of RuBP, while reductions in the CbbRII DNase I footprint were induced by fructose-1,6-bisphosphate, 3-phosphoglycerate, and KH2PO4. The current in vitro results plus recent in vivo studies suggest that CbbR-mediated regulation of cbb transcription is controlled by multiple metabolic signals in R. capsulatus. This control reflects not only intracellular levels of Calvin-Benson-Bassham cycle metabolic intermediates but also the fixed (organic) carbon status and energy charge of the cell. [ABSTRACT FROM AUTHOR]

Rhodospirillum rubrum possesses a putative intracellular poly(3-hydroxybutyrate) (PHB) depolymerase system consisting of a soluble PHB depolymerase, a heat-stable activator, and a 3-hydroxybutyrate dimer hydrolase (J. M. Merrick and M. Doudoroff, J. Bacteriol. 88:60–71, 1964). In this study we reinvestigated the soluble R. rubrum PHB depolymerase (PhaZ1). It turned out that PhaZ1 is a novel type of PHB depolymerase with unique properties. Purified PhaZ1 was specific for amorphous short-chain-length polyhydroxyalkanoates (PHA) such as native PHB, artificial PHB, and oligomer esters of (R)-3-hydroxybutyrate with 3 or more 3-hydroxybutyrate units. Atactic PHB, (S)-3-hydroxybutyrate oligomers, medium-chain-length PHA, and lipase substrates (triolein, tributyrin) were not hydrolyzed. The PHB depolymerase structural gene (phaZ1) was cloned. Its deduced amino acid sequence (37,704 Da) had no significant similarity to those of intracellular PHB depolymerases of Wautersia eutropha or of other PHB-accumulating bacteria. PhaZ1 was found to have strong amino acid homology with type-II catalytic domains of extracellular PHB depolymerases, and Ser42, Asp138, and His178 were identified as catalytic-triad amino acids, with Ser42 as the putative active site. Surprisingly, the first 23 amino acids of the PHB depolymerase previously assumed to be intracellular revealed features of classical signal peptides, and Edman sequencing of purified PhaZ1 confirmed the functionality of the predicted cleavage site. Extracellular PHB depolymerase activity was absent, and analysis of cell fractions unequivocally showed that PhaZ1 is a periplasm-located enzyme. The previously assumed intracellular activator/depolymerase system is unlikely to have a physiological function in PHB mobilization in vivo. A second gene, encoding the putative true intracellular PHB depolymerase (PhaZ2), was identified in the genome sequence of R. rubrum. [ABSTRACT FROM AUTHOR]

The photosynthetic bacterium Rhodobacter capsulatus contains two [NiFe] hydrogenases: an energy-generating hydrogenase, HupSL, and a regulatory hydrogenase, HupUV. The synthesis of HupSL is specifically activated by H[sub 2] through a signal transduction cascade comprising three proteins: the H[sub 2]-sensing HupUV protein, the histidine kinase HupT, and the transcriptional regulator HupR. Whereas a phosphotransfer between HupT and HupR was previously demonstrated, interaction between HupUV and HupT was only hypothesized based on in vivo analyses of mutant phenotypes. To visualize the in vitro interaction between HupUV and HupT proteins, a six-His (His[sub 6])-HupU fusion protein and the HupV protein were coproduced by using a homologous expression system. The two proteins copurified as a His[sub 6]-HupUHupV complex present in dimeric and tetrameric forms, both of which had H[sub 2] uptake activity. We demonstrated that HupT and HupUV interact and form stable complexes that could be separated on a native gel. Interaction was also monitored with surface plasmon resonance technology and was shown to be insensitive to salt concentration and pH changes, suggesting that the interactions involve hydrophobic residues. As expected, H[sub 2] affects the interaction between HupUV and HupT, leading to a weakening of the interaction, which is independent of the phosphate status of HupT. Several forms of HupT were tested for their ability to interact with HupUV and to complement hupT mutants. Strong interaction with HupUV was obtained with the isolated PAS domain of HupT and with inactive HupT mutated in the phosphorylable histidine residue, but only the wild-type HupT protein was able to restore normal H[sub 2] regulation. [ABSTRACT FROM AUTHOR]

Flagellar hook-basal body (HBB) complexes were purified from Rhodobacter sphaeroides. The HBB was more acid labile but more heat stable than that of Salmonella species, and protein identification revealed that HBB components were expressed only from one of the two sets of flagellar gene clusters on the R. sphaeroides genome, under the heterotrophic growth conditions tested here. [ABSTRACT FROM AUTHOR]

The phototrophic bacterium Rhodobacter capsulatus contains a single, oxygen-responsive superoxide dismutase (SOD[sub Rc]) homologous to iron-containing superoxide dismutase enzymes. Recombinant SOD[sub Rc], however, displayed higher activity after refolding with Mn[sup 2+], especially when the pH of the assay mixture was raised. SOD[sub Rc] isolated from Rhodobacter cells also preferentially contains manganese, but metal discrimination depends on the culture conditions, with iron fractions increasing from 7% in aerobic cultures up to 40% in photosynthetic cultures. Therefore, SOD[sub Rc] behaves as a Mn-containing dismutase with cambialistic properties. [ABSTRACT FROM AUTHOR]

Examines the role of Atmb on the nitrogenase activity and physiology of Rhodobacter capsulatus. Reduction of dinitrogen to ammonia; Induction of the photosynthetic bacteria; Concentration of ammonium.

Examines the role of bchP gene in encoding geranylgeranyl-bacteriophytin (Bphe) reductase in Rhodospirillum rubrum. Catalysis of Bphe reduction by bchP gene product; Classification of purple photosynthetic bacteria; Components of the reaction center of purple bacteria.

Examines the factors involved in regulating carbon dioxide fixation in Rhodobacter capsulatus and Rhodobacter sphaeroides. Isolation of mutations responsible for disrupting complex 1; Connection between the control of carbon and nitrogen metabolism to the complex I function in Rhodobacter capsulatus; Analysis of the role of complex I in redox homeostasis under phototrophic growth conditions.

Examines the rhodobacter capsulatus redox-balancing systems phototrophic metabolism. Considerations on the intracellular oxidation-reduction balancing mechanism of rhodobacter capsulatus; Specifications on the metabolic circumstance on phototrophic growth conditions; Existence of redox poise on photoheterotrophic and photoautotrophic growth.

Investigates the role of draTG and rnf genes in 2,4-dinitrophenol reduction (DNP) in the phototrophic bacterium Rhodobacter capsulatus. Effect of ammonium on DNP metabolism; Implication of the Rnf complex for nitrogen fixation and DNP reduction; Enhancement of protein nitrogen fixation by [2-oxoglutarate]/[glutamine] ratio.

Investigates the hook gene flgE expression from the flgBCDEF operon in Rhodobacter sphaeroides. Isolation of flgE gene mutants; Application of the Northern blot analysis; Characterization of the flgBCDEF operon.

Reveals that urea utilization in the phototrophic bacterium Rhodobacter capsulatus is regulated by the transcriptional activator NtrC. Genetic analyses of the R. capsulatus ure gene region; Activation of expression of ure genes under nitrogen-limiting conditions; Direct binding of NtrC to the ureD promoter.

Focuses on the characterization of the hydrogen-deuterium exchange (H-D) activities of the energy-transducing hupSL hydrogenase and H[sub 2]-signaling HupUV hydrogenase in photosynthetic bacterium Rhodobacter capsulatus. Sensitivity of the H-D exchange activity catalyzed by the HupUV protein compex to oxygen; Catalytic properties of the HupUV protein.

Deals with the isolation and characterization of canthaxanthin biosynthesis genes from the photosynthetic bacterium Bradyrhizobium species strain ORS278. Isolation of a carotenoid gene cluster; Scheme of the canthaxanthin and spirilloxanthin biosynthesis pathways; Structure of the canthaxanthin crt gene cluster.

Identifies four open reading frames, bchG in purple photosynthetic bacterium, Rhodobacter sphaeroides. Homology of bchG with bacteriochlorophyll synthetases; Accumulation of bacteriopheophorbide in mutant genes; Function of bchG in the esterification of bacteriochlorophyllide with an alcohol moiety.

Investigates the role of the AppA-PpsR antirepressor system, FnrL for the transcriptional regulation of the photosynthesis (PS) genes in Rhodobacter sphaeroides 2.4.1. Non-mediation of FnrL in the transmission of the inhibitory signal from the cbb3 oxidase; Role of Fnrl in PS gene expression; Similarity of FnrL and PrrBA activation system function.

Provides evidence of a molecular link for the coregulation of nitrogenase and hydrogenase biosynthesis in an anoxygenic photosynthetic bacterium. Control of the RegB-RegA two-component regulatory system in Rhodobacter capsulatus over molybdenum nitrogenase biosynthesis; Sources of cellular energy in photosynthetic bacteria; Role of the RegB-RegA system.

Investigates transcriptional control of gene expression for photosynthetic reaction center and light-harvesting proteins in photosynthetic bacterium Rhodovulum sulfidophilum. Conditions for synthesis of photosynthetic apparatus; Analysis of possible promoters of puf operon expression; Mechanism of oxygen-independent expression of photosynthetic genes.

Reveals that cytochrome c' (cycP) from the photosynthetic bacteria Rhodobacter capsulatus confers increased resistance to nitric oxide. Cloning and sequencing of cycP; Insertional mutagenesis of cycP; Effect of nitric oxide gas on growth rate of bacteria.

Reports on the discovery of enhanced nitrogenase activity in strains of the photosynthetic bacteria Rhodobacter capsulatus that overexpress rnf genes. Cloning of the rnfABCDFEH operon; Complementation of mutants of the bacteria; Overproduction of rnf gene products in strains carrying pNR117.

Studies the novel variant of Ubihydroquinone-cytochrome c oxidoreductase named cytochrome b6c1 complex with a split cytochrome b that supports photosynthetic growth of Rhodobacter capsulatus. Effect of mutagenesis; C-to-T transition; Electron paramagnetic spectroscopy; Inhibitor resistance; Redox potential differences.

Studies photosynthetic regulatory genes regA and regB from Rhodovulum sulfidophilum, Roseobacter denitrificans, and Rhodobacter capsulatus. Cloning and seqience analysis of the photosynthesis regulatory gene cluster of Rhodovulum sulfidophilum and Roseobacter denitrificans; Complementation analysis of regulatory genes among different species.

Studies the means by which photosynthetic bacteria harvest solar energy. Structure of light-harvesting 1 and reaction center (LH1-RC) complexes; Evolution of antenna complexes to increase the effective cross-sectional area for light absorption of each reaction center; Energy transfer within the bacterial photosynthetic unit.

Shows that the photosynthetic bacterium Rhodobacter capsulatus regulates its nitrogenase by covalent modification via the reversible ADP-ribosylation of iron protein in response to darkness of addition of external NH4+. Bacterial strains and growth conditions; Assimilation requirements; Continuous cultivation under NH4+ limitation.

Provides information on a study which demonstrated that the photosynthetic bacterium Rhodobacter capsulatus carry out nitrogenase `switch off.' Review of related literature; Effects of ammonium additions on nitrogenase activity; Conclusions.

Measures the photoresponse of two purple nonsulfur bacteria, Rhodobacter sphaeroides and Rhodospirillum centenum, under defined conditions in a light beam propagating at 90 degrees to the optical axis of the microscope. Effect of this beam on cells; Results obtained; Comparison of liquid-grown R. centenum to surface-grown R. centenum; Findings of this comparison.

Presents a study which used transposon mutagenesis to obtain nonmotile flagellar mutants from the photosynthetic bacterium, Rhodobacter sphaeroides. Isolation and characterization of a mutant that illustrates a polyhook phenotype; Technique utilized for the morphological characterization of the mutant; How polyhooks were obtained; Results obtained from experiments conducted.

Focuses on the specialized photosynthetic membrane, a rhodobacter sphaeroides which synthesizes upon reduction of the O2 tension below threshold levels. Description of the prrB and prrA genes; Reference to the prrC gene; Detailed information provided on rhodobacter sphaeroides.

Studies Rhodobacter capsulatus CycH, a bipartite gene product with pleiotropic effects on the biogenesis of structurally different c-type cytochromes. Bacterial strains and growth conditions; Molecular genetic techniques; Biochemical techniques; Nucleotide sequence accession number; Photosynthetic and respiratory electron transport pathways.

Examines whether the hupTUV operon is involved in negative control of hydrogenase synthesis in Rhodobacter capsulatus. Bacterial strains and cultures; DNA preparation and bacterial mating; Nucleotide and protein sequence studies; Overexpression of the hupU and hupV genes in Escherichia coli; Interposon mutagenesis of the hupV gene.

Reports on the sequencing of the Chloroflexus aurantiacus open reading frame thought to be the C. aurantiacus homolog of the Rhodobacter capsulatus bchG gene. Nucleotide sequence and derived amino acid sequence; Sequencing of the C. aurantiacus bchG gene; Sequence comparisons.

Presents information on a study which constructed and evaluated Rhodobacter capsulatus puhA mutant strains containing either a nonpolar or polar insertion of an antibiotic resistance cartridge for their photosynthetic growth properties, absorption spectroscopy profiles, and chromatophore protein compositions. What structural studies of purified light-harvesting (LH) complexes have shown; Bacterial strains and plasmids used in study.

Describes the cloning, sequencing and expression of the Rhodobacter sphaeroides pgsA gene encoding phosphatidylglycerophosphate synthase in both R. sphaeroides and Escherichia coli. DNA sequence of plasmid pBSP8; Overexpression of PgsARs in R. sphaeroides; Phospholipid composition.

Describes a genetic selection that uses transposon mutagenesis to identify loci affecting the aerobic expression of the hemA gene of Rhodobacter sphaeroides. Defining the region upstream of hemA required for aerobically regulated expression; Transposon-induced trans-acting mutations affecting the expression of hemA.

Demonstrates the photosynthetic bacteria, Rhodobacter capsulatus contains a gene, termed senC, that is a homolog of the yeast SCO1 gene. Bacterial strains and culture conditions; Genomic library construction and cloning; Sequence analysis; Genetic manipulations; Nucleotide sequence accession number.

Investigates the resistance of the photosynthetic eubacterium Rhodobacter sphaeroides to ultraviolet radiation. Isolation and mapping of DNA repair-deficient mutants; Characterization of mutants; Cloning of transposon insertions.