DNA-DNA hybridization of Rhodopseudomonas capsulata,Rhodopseudomonas sphaeroides and Rhodopseudomonas sulfidophila strains

The genetic relatedness of 21 Rhodopseudomonas strains has been studied by means of DNA-DNA hybridization. All strains included in the study belonged to the subgroup of the genus Rhodopseudomonas which is characterized by a short-rod to coccus morphology, a vesicular intracytoplasmic membrane system and carotenoids of the spheroidene group. Mol percentages guanine + cytosine ranged from 64 to 73, most strains having values between 68 and 72. With few exceptions, the hybridization data obtained were in agreement with the subdivision in three (or possibly four) species on the basis of classical taxonomy. Strain SCJ, formerly considered to be a somewhat atypical R. capsulata strain, is most probably a R. sphaeroides strain and two out of seven strains that were received as R. sulfidophila did not fit in this species on the basis of the hybridization data. The results also showed that two undesignated strains that were previously thought to be related to R. capsulata (Hansen et al. 1975) cannot be assigned to this species and may be representatives of another species. The seven strains that required approximately 2.5% NaCl in the medium and that had been designated R. sulfidophila were found to synthesize far higher levels of bacteriochlorophyll during fully aerobic growth in the dark than the purple bacteria studied thus far.Abbreviations GC guanosine + cytosine - SSC standard saline citrate buffer     

Characterization of the plasmid DNAs of Rhodopseudomonas capsulata

Presence of extrachromosomal DNa in Rhodopseudomonas capsulata strain BH9 was shown by the appearance of a satellite band in a dye-buoyant density gradient. Radioactively labelled DNA was prepared from this satellite band and examined on a 5–20% sucrose gradient. Three radioactive peaks with sedimentation coefficients of 100 S, 94 S, and 58–64 S, respectively, were consistently observed. Analysis of these sedimentation coefficients suggested that there are two species of plasmid DNA with molecular sizes of 94×10⁶ daltons (named pBH91) and 74×10⁶ daltons (named pBH92). The 58–64 S peak is attributed to open circular molecules. DNAs from each peak of the sucrose gradient were examined by electronmicroscopy, and the results agree closely with those of the sucrose gradient analysis. Reassociation kinetics of the plasmid DNA was also followed. Addition of total DNA of strain BH9 increased the renaturation rate of the plasmid DNA. It was calculated from the magnitude of the increase that approximately 10% of the BH9 total DNA may hybridize with the plasmid sequences. DNA prepared from the gene transfer agent (GTA) produced by R. capsulata increases the renaturation rate of the plasmid to the same extent as total DNA isolated from the GTA producing strain, Y262.     

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 10³–10⁵ 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.     

Modulation by fumarate of a P i -insensitive pyruvate kinase from Rhodopseudomonas capsulata

Cold lability was found to be responsible for the initial failure to detect pyruvate kinase activity in extracts of the facultative phototroph, Rhodopseudomonas capsulata. Taking advantage of the reversal of cold inactivation by high concentrations of monovalent cations, the enzyme could be partially purified by (NH₄)₂SO₄-precipitation and gelfiltration. In contrast to the enzyme from Rhodospirillum rubrum, the pyruvate kinase from R. capsulata is nearly insensitive to inorganic phosphate. Instead, it is susceptible to allosteric inhibition by fumarate. Adenosinemonophosphate and sugar phosphates as activators prevent the inhibitory action of fumarate.     

Respiratory deficient mutants of Rhodopseudomonas capsulata

The facultative photosynthetic bacterium Rhodopseudomonas capsulata was mutagenized by transfer of the plasmid pSUP201::Tn5 from Escherichia coli to R. capsulata. Mutants defective in cytochrome oxidase and other respiratory functions were selected by replica plating, NADI-reaction and immunological methods. Among 20,000 mutants no clone was detected, which lacks the 65,000-protein of the cytochrome oxidase, but many mutants have been isolated which were cytochrome oxidase deficient (or inactive). Other mutants excrete heme and cytochrome c into the medium and lack cytochrome c ₂.Abbreviations Ap ampicillin - CIE crossed immunoelectrophoresis - cyt cytochrome - Cm chloramphenicol - Km kanamycin - SDS sodium dodecylsulfate - Tc tetracycline     

Ammonium uptake in Rhodopseudomonas capsulata

Investigations of the uptake of ammonium (NH ₄ ⁺ ) by Rhodopseudomonas capsulata B100 supported the presence of an NH ₄ ⁺ transport system. Experimentally NH ₄ ⁺ was determined by electrode or indophenol assay and saturation kinetics were observed with two apparent K _m's of 1.7 M and 11.1 M (pH 6.8, 30°) and a V _max at saturation of 50–60 nmol/min·mg protein. The optimum pH and temperature were 7.0 and 33° C, respectively. The Q₁₀ quotient was calculated to be 1.9 at 100 M NH ₄ ⁺ , indicating enzymatic involvement. In contrast to the wild type, B100, excretion of NH ₄ ⁺ , not uptake, was observed in a glutamine auxotroph, R. capsulata G29, which is derepressed for nitrogenase and lacks glutamine synthetase activity. G29R1, a revertant of G29, also took up NH ₄ ⁺ at the same rate as wild type and had fully restored glutamine synthetase activity. Partially restored derivatives, G29R5 and G29R6, grew more slowly than wild type on NH ₄ ⁺ as the nitrogen source, remained derepressed for nitrogenase in the presence of NH ₄ ⁺ , and displayed rates of NH ₄ ⁺ uptake in proportion to their glutamine synthetase activity. Ammonium uptake and glutamine synthetase activity were also restored in R. capsulata G29 exconjugants which had received the plasmid pPS25, containing the R. capsulata glutamine synthetase structural gene. These data suggest that NH ₄ ⁺ transport is tightly coupled to assimilation.Abbreviations used CHES cyclohexylaminoethanesulfonic acid - GS glutamine synthetase - SDS sodium dodecylsulfate     

Photoheterotrophic utilization of acetate by the wild type and an acetate-adapted mutant of Rhodopseudomonas capsulata

Rhodopseudomonas capsulata strain St. Louis can grow anaerobically in the light-with acetate as the carbon source. The organism is sensitive to acetate, however, initial concentrations exceeding 25 mM resulting in an extensive growth lag. Bicarbonate is not required for growth of this strain on acetate, but addition of bicarbonate shortens the lag phase in media with high initial acetate concentration. A spontaneous mutant which exhibited a minimal lag phase and rapid growth rates on acetate media was derived from strain St. Louis. This mutant possessed elevated levels of the glyoxylate cycle enzyme, isocitrate lyase.     

The influence of acetate on the oxidation of sulfide by Rhodopseudomonas capsulata

The capacity to oxidize sulfide and the influence of the simultaneous presence of acetate in heterotrophically (acetate) and autotrophically (sulfide/CO₂) grown Rhodopseudomonas capsulata was investigated.Sulfide oxidation of acetate-limited cultures was found inversely related to the specific growth rate. Upon acetate deprevation (metering pump stopped) increased rates of sulfide oxidation were observed. This points to the existence of a constitutive acceptor for the electrons from sulfide. It is suggested that a carrier functional in the light-induced cyclic electron flow operates as such. The rate of sulfide oxidation, however, is low when compared to autotrophically-grown cells. This is probably due to the low levels of Calvin cycle enzymes present in the acetate-grown cells.In cells growing on sulfide/CO₂, the addition of acetate resulted in less sulfide being oxidized. Upon depletion of the acetate, the rate of sulfide oxidation again increased, however, insufficiently to maintain the accelerated growth rate. This indicates that under mixotrophic conditions the enzymes of the Calvin cycle are being synthesized to a far lesser extent.Non-Standurd Abbreviations PHB poly--hydroxybutyric acid - D dilution rate - TCA Tri carboxylic acid cycle - RubPcase ribulose 1,5-bisphosphate carboxylase - RP reducing power     

Regulation of isocitrate lyase in a mutant of Rhodopseudomonas capsulata adapted to growth on acetate

Studies on acetate utilization by Rhodopseudomonas capsulata strain St. Louis indicated that the wild type grew poorly on acetate and made little if any of the glyoxylate cycle enzyme isocitrate lyase. A spontaneous mutant, Ac-l, capable of vigorous and immediate growth on acetate and exhibiting high levels of isocitrate lyase activity, was isolated in the course of those studies.Isocitrate lyase was not formed when the mutant was grown on malate. Addition of malate to cultures of Ac-l growing on acetate resulted in loss of the enzyme by dilution through growth.Starvation of acetate-grown Ac-l for acetate resulted in a rapid and complete loss of isocitrate lyase activity which was shown to be energy dependent. Readdition of acetate to a starved culture previously grown on acetate resulted in a rapid recovery of enzyme activity. The recovery required energy and was sensitive to chloramphenicol inhibition at any time during the recovery phase.     

A comparison of electron transport and photophosphorylation systems of Rhodopseudomonas capsulata and Rhodospirillum rubrum

The photophosphorylation systems of Rhodopseudomonas capsulata and Rhodospirillum rubrum chromatophores have been compared in respect to the effects of artificial electron carries [N-methyl-phenazonium methosulfate (PMS) and diaminodurene], reducing agents (ascorbate in particular), and various quinones in the absence and presence of the electron transport inhibitors antimycin A and dibromothymoquinone (DBMIB). In addition, the effects of both inhibitors on photosynthetic electron transport through cytochromes b and c has been followed. From the results obtained, it appears that in both organisms: a) ubiquinone functions as an electron carrier between the cytochromes, and b) both antimycin A and DBMIB inhibit cyclic electron flow in the segment ... cytochrome bubiquinone»cytochrome c ..., but at different sites. The systems apparently differ mainly in respect to the nature of the electron flow by-pass shunt that is evoked in the presence of PMS; thus, in R. rubrum, PMS catalyzes a shunt that by-passes both cytochrome b and ubiquinone, whereas in Rps. capsulata the PMS shunt seems to circumvent only ubiquinone.Abbreviations BChl bacteriochlorophyll - DAD diaminodurene=2,3,5,6-tetramethyl-p-phenylenediamine - DBMIB dibromothymoquinone=2,5-dibromo-6-isopropyl-3-methylbenzoquinone - HOQNO heptylhydroxyquinoline-N-oxide - PMS N-methylphenazonium methosulfate     

On insertion of pigment-associated polypeptides during membrane biogenesis in Rhodopseudomonas capsulata

Early stages in the formation of membranes and photosynthetic units were studied under growth-limiting phototrophic and chemotrophic conditions in cells of Rhodopseudomonas capsulata. The incorporation of polypeptides, forming bacteriochlorophyll-carotinoid-protein complexes in the membrane, was followed by use of pulse-labeling and immunoprecipitation techniques. The newly synthesized polypeptides were inserted into two distinct membrane fractions at both different rates and proportions. The two membrane fractions differed in sedimentation behavior, absorption spectra and activities of the respiratory chain. The individual pigment-associated proteins did not exhibit precursor-product relationship between the two membrane fractions. The data suggest that newly synthesized polypeptides were integrated both into cytoplasmic and pre-existing intracytoplasmic membranes, where the proteins and pigments were assembled to form reaction centers and light-harvesting pigment-protein complexes.Abbreviations Bchl bacteriochlorophyll - cpm counts per minute - M _r relative molecular mass - P 100 pellet of 100,000xg, 60 min - P300 pellet of 300,000xg, 90 min - pO₂ oxygen partial pressure - R Rhodopseudomonas - dodecyl sulfate sodium dodecyl sulfate. International standard units - Bq Becquerel (s^-1) - Pa Pascal (N/m²; 1 Torr=133,3 Pa)     

Diazotrophic growth of Rhodopseudomonas acidophila and Rhodopseudomonas capsulata under microaerobic conditions in the dark

Diazotrophy of Rhodopseudomonas acidophila and Rhodopseudomonas capsulata was not obligatorily linked to photosynthesis. In the dark R. acidophila grew with dinitrogen as sole nitrogen source at a dissolved oxygen tension of 15 Torr (= 2.0 kPa); the doubling time was 8 h. Acetylene reduction by whole cells was more sensitive to oxygen in the light than in the dark. 16.5 mg N₂ were fixed per g lactic acid consumed. R. capsulata synthesized nitrogenase and fixed dinitrogen in the dark at a dissolved oxygen tension of less than one Torr (= 0.13 kPa). The doubling time of this bacterium was 16 h and 10.5 mg N₂ were fixed per g lactic acid consumed.Abbreviation kPa kilopascal     

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.     

Oxygen inhibition of the photoassimilation of CO2 in Rhodopseudomonas capsulata

The photoassimilation of ¹⁴CO₂ by washed cells of the photosynthetic bacterium Rhodopseudomonas capsulata was greatly inhibited in air. The inhibition was partially reversed by either sparging with argon or by adding inhibitors, e.g. CO [50% (v/v) in air] and NaN₃ (0.2 mM), which at these concentrations effectively restricted respiration. The effect of oxygen on the photoassimilation of ¹⁴CO₂ may be associated with a change in the redox state of the cells resulting in less reducing equivalents being available for this process.     

A pleiotropic mutant of Rhodopseudomonas capsulata defective in nitrogen metabolism

Wild type strains of Rhodopseudomonas capsulata typically can use N₂, NH ₄ ⁺ , or various nitrogenous organic compounds as N sources for photosynthetic growth. One class of mutants selected for inability to grow on N₂ (Nif^–) also shows simultaneous loss of capacity to obtain N from numerous organic substrates. When supplied at relatively high concentrations, ammonia can be used as the sole N source for growth of such strains. Enzymatic analysis of one mutant (W11) indicates that the pleiotropic effect on N nutrition is neither due to detectable alteration in the activities of nitrogenase or the initial enzymes responsible for bulk assimilation of ammonia (glutamine synthetase and glutamate synthase) nor to absence of systems required for catabolism of organic N sources. The phenotype of W11 (Nit^–; defective in N metabolism) appears to result from loss of ability to grow using low concentrations of ammonia (supplied externally or generated in vivo).     

Evidence for an involvement of glutamine synthetase in regulation of nitrogenase activity in Rhodopseudomonas capsulata

In the presnet studies with whole cells and extracts of the photosynthetic bacterium Rhodopseudomonas capsulata the rapid inhibition of nitrogenase dependent activities (i.e. N₂-fixation acetylene reduction, or photoproduction of H₂) by ammonia was investigated. The results suggest, that the regulation of the nitrogenase activity by NH ₄ ⁺ in R. capsulata is mediated by glutamine synthetase (GS). (i) The glutamate analogue methionine sulfoximine (MSX) inhibited GS in situ and in vitro, and simultaneously prevented nitrogenase activity in vivo. (ii) When added to growing cultures ammonia caused rapid adenylylation of GS whereas MSX abolished the activity of both the adenylylated and unadenylylated form of the enzyme. (iii) Recommencement of H₂ production due to an exhaustion of ammonia coincided with the deadenylylation of GS. (iv) In extracts, the nitrogenase was found to be inactive only when NH ₄ ⁺ or MSX were added to intact cells. Subsequently the cells had to be treated with cetyltrimethylammonium bromide (CTAB). (v) In extracts the nitrogenase activity declined linearily with an increase of the ration of adenylylated vs. deadenylylated GS. A mechanism for inhibition of nitrogenase activity by ammonia and MSX is discussed.Abbreviations BSA bovin serum albumine - CTAB cetyltrimethylammonium bromide - GOGAT l-glutamine: 2-oxoglutarate amino transferase - GS glutamine synthetase - HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid - MSX l-methionine-d,l-sulfoximine     

Characterization of three membrane fractions isolated from cells of Rhodopseudomonas capsulata adapting from chemotrophic to phototrophic conditions

By means of sucrose density centrifugation three membrane fractions, named light, medium and heavy have been isolated from cells of Rhodopseudomonas capsulata strain 37b4, adapting from chemotrophic to phototrophic growth conditions. Succinate dehydrogenase activity of aerobically grown cells was mainly confined to the heavy (chromatophore) fraction. Upon changing to phototrophic conditions the activity of the succinate dehydrogenase increased in the medium and light fraction. All fractions contain bacteriochlorophyll. NADH dehydrogenase of chemotrophically grown cells was enriched in the light and medium fraction but is increased in the heavy fraction under phototrophic growth conditions. The capacity of photophosphorylation is high in the light and heavy fraction. The results indicate a differentially incorporation of functional subunits into specific parts of the membrane system during membrane differentiation.Abbreviations Bchl bacteriochlorophyll - CCCP carbonyl cyanide m-chlorophenyl hydrazone - DCCD N,N-dicyclohexyl carbodiimide     

Nickel uptake in Rhodopseudomonas capsulata

Nickel uptake system was investigated with a wild-type cell of Rhodopseudomonas capsulata and two mutants lacking uptake hydrogenase (Hup^-). Wild type cells grown photoheterotrophically incorporated ⁶³Ni²⁺ by a high affinity system. The uptake system had a pH of 7.0 and a temperature optimum of 28°C. Both Mg²⁺ and Co²⁺ ions severely repressed the uptake of Ni²⁺. Nickel transport was also inhibited by metabolic inhibitors including cyanide, azide, 2,4-dinitrophenol and m-chlorophenyl carbonylcyanidehydrazone. These data imply that Ni²⁺ uptake system occurs by the energy-linked system for Mg²⁺ transport. The intracellular distribution of ⁶³Ni²⁺ in Hup^- cells showed the same pattern as that of wild-type cells, indicate that the Hup^- strains have no deficiency in Ni²⁺ transport.Abbreviations CCCP m-chlorophenyl carbonylcyanidehydrazone - HEPES N-2-hydroxylethylpiperazine-N-2-ethane-sulfuric acid - HOQNO 2-n-nonly-4-hydroxyquinoline-N-oxide - TMA tetramethylammonium hydroxide     

Immunoelectrophoretic approach to the metabolic regulation of glutamine synthetase in Rhodopseudomonas capsulata E1F1: role of glutamine

Anti-glutamine synthetase serum was raised in rabbits by injecting purified glutamine synthetase (GS) of the phototrophic bacterium Rhodopseudomonas capsulata E1F1. The antibodies were purified to monospecificity by immunoaffinity chromatography in GS-sepharose gel. These anti-GS antibodies were used to measure the antigen levels in crude extracts from bacteria, grown phototrophically with dinitrogen, nitrate, nitrite, ammonia, glutamate, glutamine or alanine as nitrogen sources. The amount of GS detected by rocket immunoelectrophoresis was proportional to Mn²⁺-dependent transferase activity measured in the crude extracts. Addition of GS inhibitor l-methionine-d,l-sulfoximine (MSX) to the actively growing cells promoted increased antigen levels, that were not found in the presence of glutamine or chloramphenicol. The ammonia-induced decrease in GS relative levels was reverted by MSX. GS levels remained constant when phototrophically growing cells were kept in the dark.Abbreviations GS glutamine synthetase - MOPS 2-(N-morpholine) propane sulfonate - MSX l-methionine-d,l-sulfoximine     

Oxidative degradation of purines by the faculative phototrophic bacterium Rhodopseudomonas capsulata

The mechanism of purine degradation was studied in the facultative phototrophic bacterium Rhodopseudomonas capsulata. Using tungstate as an inhibitor of synthesis of an active xanthine dehydrogenase it could be shown in growth experiments that purine compounds are transformed to uric acid as central purine intermediate prior to ring cleavage. Because of its rapid degradation, the mechanism of uric acid conversion was investigated using 1-methyluric acid as substrate. The analogue was partially degraded by whole cells yielding 3-methylallantoin and methylurea. This implicated an oxidative degradation of 1-methyluric acid analogous to oxidation of uric acid to allantoin suggesting uric acid degradation via allantoin. In cell-free extracts, allantoinase, allantoicase, ureidoglycolase and urease activities degrading allantoin to NH₃, CO₂ and glyoxylic acid were detected. Apparently, purine degradation in R. capsulata proceeds in a manner similar to many aerobic microorganisms. It is peculiar to this bacterium, however, that the pathway evidently operates also under anaerobic conditions. In cell extracts, oxidation of uric acid was observed which could be increased by addition of cytochrome c. The basis of this stimulation is still unknown.