Trimethylamine N-oxide respiration by aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114

Erythrobacter sp. OCh 114, an aerobic photosynthetic bacterium, had trimethylamine N-oxide (TMAO) reductase activity, which increased when the culture medium contained TMAO. The reductase was located in the periplasm. The bacteria grew anaerobically in the presence of TMAO. These results suggested that Erythrobacter OCh 114 has the ability to reduce TMAO through the respiratory chain. The TMAO respiration system of this organism was different from those of facultative purple photosynthetic bacteria in two respects: (a) TMAO reductase did not have activity to reduce dimethyl sulfoxide and (b) soluble c-type cytochrome, cytochrome c551, and cytochrome b-c1 complex appeared to be involved. The photochemical activity, which is usually inoperative in the anaerobic cell suspension, was restored by TMAO, suggesting that the photosynthesis and the TMAO respiration share a common electron transfer chain.     

Reaction center complex from an aerobic photosynthetic bacterium,Erythrobacter species OCh 114

A photosynthetic reaction center complex has been purified from an aerobic photosynthetic bacterium, Erythrobacter species OCh 114. The reaction center was solubilized with 0.45% lauryldimethylamine N-oxide and purified by DEAE-Sephacel column chromatography. Absorption spectra of both reduced and oxidized forms of the reaction center were very similar to those of the reaction center from Rhodopseudomonas sphaeroides R-26 except for the contributions due to cytochrome and carotenoid. 1 mol reaction center contained 4 mol bacteriochlorophyll a, 2 mol bacteriopheophytin a, 4 mol cytochrome c-554, 2 mol ubiquinone-10, and carotenoid. The reaction center consisted of four different polypeptides of 26, 30, 32 and 42 kDa. The last one retained heme c. Absorbance at 450 nm oscillated with the period of two on consecutive flashes. The light-minus-dark difference spectrum had two peaks at 450 nm and 420 nm, indicating that odd flashes generated a stable ubisemiquinone anion and even flashes generated quinol. o-Phenanthroline accelerated the re-reduction of flash-oxidized reaction centers, indicating that o-phenanthroline inhibited the electron transfer between Q_A and Q_B. The cytochrome (cytochrome c-554) in the reaction center was oxidized on flash activation. The midpoint potential of the primary electron acceptor (Q_A) was determined by measuring the extent of oxidation of cytochrome c-554 at various ambient potentials. The mid-point potential of Q_A was −44 mV, irrespective of pH between 5.5 and 5.9.     

Two types of cytochrome cd1 in the aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114

Components I and II of cytochrome cd1 which had different spectral features were purified from the aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh 114. Component I showed an absorption maxima at 700 and 406 nm in the oxidized form, and at 621, 552.5, 548 and 416 nm in the reduced form. Component II showed an absorption maxima at 635 and 410 nm in the oxidized form and at 628, 552.5, 548 and 417 nm in the reduced form. The relative molecular mass, Mr, of both cytochromes was determined to be 135,000 with two identical subunits. Components I and II showed pI values of 7.6 and 6.8, respectively. The redox potential of hemes ranged from +234 mV to +242 mV, except for the heme d1 of component I (Em7 = +134 mV). Components I and II showed both cytochrome c oxidase and nitrite reductase activities. Cytochrome c oxidase activity was strongly inhibited by a low concentration of nitrite and cyanide. Erythrobacter cytochromes c-551 and c-552 were utilized as electron donors for the cytochrome c oxidase reaction. The high affinity of cytochrome c-552 to component II (Km = 1.27 microM) suggested a physiological significance for this cytochrome. Erythrobacter cytochromes cd1 are unique in their presence in cells grown under aerobic conditions as compared to other bacterial cytochromes cd1 which are formed only under denitrifying conditions.     

Inhibition of porphyrin biosynthesis by exogenous 5-aminolevulinic acid in an aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114

Exogenously administered 5-aminolevulinic acid (ALA) inhibited the formation of bacteriochlorophyll a (Bchl a) in a dose-dependent manner in the aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh 114, under dark growth conditions. The ALA concentration required for half-inhibition after 24-h growth was estimated to be about 3.0 mM. Porphyrin and Bchl precursors were not found in either the cells or the growth medium. The same inhibition was also observed with cytochrome c formation. When ALA was incubated with intact cells, a large amount of ALA was converted to an unknown metabolite. The pH optimum of the conversion was 7.8. The metabolite did not react with Ehrlich's reagent, but did so with ninhydrin, giving a yellow color. Based on analyses by several techniques including mass spectrometry, ir spectrometry, and paper electrophoresis, it was identified as 4-hydroxy-5-aminovaleric acid (HAVA). Authentic HAVA prepared from ALA was a competitive inhibitor of the enzyme, porphobilinogen synthase of Erythrobacter. The Ki value for authentic HAVA was calculated to be 2.4 mM from a Dixon plot and the HAVA concentration required for half-inhibition was 17 mM. It is concluded that in Erythrobacter cells, exogenous ALA is converted to the metabolite, HAVA, which is responsible for the inhibition of porphobilinogen synthase as well as that of Bchl a and cytochrome formation.     

A novel phosphatase specific for pyridoxal 5'-phosphate in an aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114

Abstract An acid phosphatase highly spcific for pyridoxal 5'-phosphate (PLP) was found and partially purified from the aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114. The enzyme showed a pH optimum at 5.5; its activity was stimulated by magnesium ions. This enzyme also hydrolyzed p -nitrophenyl phosphate (NPP) and flavin mononucleotide (FMN). The enzyme level varied depending on growth conditions. Supplementing the growth medium with glycerol, glucose, xylose or mannitol increased the level of phosphatase activity. An inverse relationship between free phosphate content in the cells and enzyme level was observed.     

Roles of bacteriochlorophyll and carotenoid synthesis in formation of intracytoplasmic membrane systems and pigment-protein complexes in an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114.

Synthesis of bacteriochlorophyll and carotenoids was inhibited in an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114, by alpha, alpha'-dipyridyl and diphenylamine. Formation of two pigment-protein complexes, reaction center-B870 (RC-B870) and B806, and development of the intracytoplasmic membranes of the cells were studied by spectral analysis and electron microscopy. Inhibition of bacteriochlorophyll synthesis by alpha, alpha'-dipyridyl, which was accompanied by a decrease in carotenoid synthesis, suppressed formation of intracytoplasmic membranes in the cells. Growth under illumination had a similar effect on formation of pigments and membranes. On the other hand, inhibition of carotenoid synthesis by diphenylamine did not suppress either development of the membrane system or bacteriochlorophyll synthesis. Formation of RC-B870 and B806 complexes, however, was differentially affected by blockage of carotenoid synthesis. In the presence of diphenylamine, the B806 complex was formed in a much smaller amount than the RC-B870 complex. These results suggest that, in Erythrobacter sp. strain OCh114, bacteriochlorophyll plays an essential role in intracytoplasmic membrane development, and carotenoids are important for assembly of pigment-protein complexes.     

Photophosphorylation and oxidative phosphorylation in intact cells and chromatophores of an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114.

Light-induced ATP synthesis was studied in intact cells and chromatophores of Erythrobacter sp. strain OCh114. ATP synthesis was measured by both the pH method and the luciferin-luciferase luminescence method. The rate of ATP synthesis was moderate (a typical value of 0.65 mol of ATP per mol of bacteriochlorophyll per min), and synthesis was inhibited by antimycin A. ATP was synthesized under illumination only under aerobic conditions and not under anaerobic conditions. This characteristic was similar to that of other light-induced energy transduction processes in this bacterial species, such as oxidation of reaction center, oxidation of cytochrome c551, and translocation of H+, which were not observed under anaerobic conditions. This phenomenon was reconciled with the fact that the Erythrobacter sp. could not grow anaerobically even in the light. The characteristics of oxidative phosphorylation and ATP hydrolysis were also investigated. The respiratory ratio of chromatophores was 2.3. Typical rates of oxidative phosphorylation by NADH and by succinate were 2.9 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.22) and 1.1 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.19), respectively. A typical rate of ATP hydrolysis was 0.25 mol of ATP per mol of bacteriochlorophyll per min in chromatophores. ATPase and adenylate kinase are also involved in the metabolism of adenine nucleotides in this bacterium.     

Bacteriochlorophyll-protein complexes of aerobic bacteria,Erythrobacter longus and Erythrobacter species OCh 114

Bacteriochlorophyll(Bchl)-protein complexes were isolated from obligate aerobic bacteria, Erythrobacter longus and Erythrobacter species OCh 114. The apparent molecular weights, absorption spectra and polypeptide compositions of the light-harvesting complexes were, in general, similar to those of the light-harvesting Bchl-protein complexes of purple photosynthetic bacteria. The reaction center complexes of these bacteria also showed similar properties to those of the purple bacteria except for slightly altered polypeptides. However, the following characteristic features of the light-harvesting systems were found in these aerobic bacteria. Major carotenoids were not bound to the Bchl-protein complex in E. longus. In Erythrobacter sp. OCh 114, a new type of Bchl-protein complex which showed a single absorption band in the near infrared region at 806 nm was obtained. The reaction center of strain OCh 114 was associated with a c-type cytochrome.Abbreviations Bchl bacteriochlorophyll a - RC reaction center - SDS sodium dodecylsulfate - PAGE polyacrylamide gel electrophoresis     

A Denitrifying Activity in an Aerobic Photosynthetic Bacterium, Erythrobacter sp. Strain OCh 114

An aerobic photosynthetic bacterium, Erythrobacter sp. strainOCh 114, was capable of growth under anaerobic conditions inthe dark with nitrate as a terminal electron acceptor. The optimalnitrate concentration was about 6 mM for anaerobic growth, althougha wide range of concentrations from 1 to 400 mM were effective.A large amount of N₂O gas was released during this anaerobicgrowth, indicating a denitrifying activity in this bacterium.Light had no stimulating or inhibiting effect on the rates ofanaerobic growth and gas release. The enzymes responsible forthe denitrifying activity, dissimilatory nitrate and nitritereductases, were present in aerobically grown cells. (Received February 19, 1988; Accepted May 16, 1988)     

Characterization of Porphobilinogen Synthase from an Aerobic Photosynthetic Bacterium, Erythrobacter sp. Strain OCh 114

Porphobilinogen synthase (formerly 5-aminolevulinic acid dehydratase,EC 4.2.1.24 [EC] ) was purified 7,405-fold from an aerobic photosyntheticbacterium, Erythrobacter sp. strain OCh 114. The molecular weightof the enzyme was determined to be 260,000 by Sephadex G-200gel filtration. The enzyme had a single pH optimum at 8.0 andshowed no requirement for metal ion and thiol compound for itsmaximum activity. The K_m value for 5-aminolevulinic acid was0.29 mM. 4,5-Dioxovaleric acid and levulinic acid were foundto be competitive inhibitors of the enzyme, with K_i values of0.65 and 0.80 mM, respectively. The enzyme was extremely labilein acidic pH and almost completely lost its activity within1 h at pH 6.0 and 30?C. This Erythrobacter enzyme seems to besimilar to the enzyme from the anaerobic photosynthetic bacteriumRhodobacter capsulatus in its molecular and catalytic properties. (Received February 17, 1988; Accepted May 9, 1988)     

Excitation and Emission Spectroscopy of Membranes and Pigment-protein Complexes of an Aerobic Photosynthetic Bacterium, Erythrobacter sp. OCh 114

Emission and excitation spectra of steady-state fluorescencefrom membranes and isolated pigment-protein complexes of anaerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114 indicated high efficiency of energy transfer from Bchl 806to Bchl 870 and from carotenoids to bacteriochlorophyll. Thus,this bacterium has a highly efficient light-harvesting systemtypical of photosynthetic bacteria. (Received August 3, 1989; Accepted January 27, 1990)     

In vivo states and functions of carotenoids in an aerobic photosynthetic bacterium,Erythrobacter longus

In vivo states and functions of carotenoids in the membranes and the isolated RC-B865 pigment-protein complexes from an aerobic photosynthetic bacterium, Erythrobacter longus, are investigated by means of fluorescence excitation and resonance Raman (RR) spectra. Erythroxanthin sulfate, a dominant carotenoid species in the membranes (>70%), is found not to transfer the absorbed light energy to bacteriochlorophyll (Bchl), and its RR spectra are similar between the in vivo and in vitro states. These observations indicate that erythroxanthin sulfate does not interact with either Bchl or proteins in the membranes, and suggest that its function may be limited to photoprotection by quenching the harmful singlet oxygen. On the other hand, two other carotenoid species contained in the isolated RC-B865 complexes, zeaxanthin and bacteriorubixanthinal, have a high efficiency of energy transfer to Bchl (88±5%). The RR spectra of these two carotenoids, each of which can be selectively obtained by choosing the excitation wavelength, show some characteristics of interactions with proteins or Bchl.Abbreviations Bchl bacteriochlorophyll a - FWHM full width at half maximum - PAGE polyacrylamide gel electrophoresis - RC reaction center - RR resonance Raman - SDS sodium dodecyl sulfate     

Light-induced changes of carotenoid pigments in anaerobic cells of the aerobic photosynthetic bacterium,Roseobacter denitrificans (Erythrobacter species OCh 114): reduction of spheroidenone to 3,4-dihydrospheroidenone

Roseobacter denitrificans, previously named Erythrobacter species OCh 114, synthesized spheroidenone as a major carotenoid under aerobic dark conditions. When the dark-grown cells were subjected to illumination under anacrobic conditions, many unknown yellow pigments appeared and a considerable amount of spheroidenone disappeared. Absorption maxima of these pigments were blue-shifted from those of spheroidenone. The most abundant of the pigments was isolated, and its chemical structure was determined as 3,4-dihydrospheroidenone on spectroscopic and chemical evidence. Presumably, over-reduction of the photosynthetic apparatus interfered with normal photosynthetic electron transfer and resulted in photoreduction of C=C double bond at the 3,4-position of spheroidenone.     

Photochemical Activities of Bacteriochlorophyll in Aerobically Grown Cells of Aerobic Heterotrophs, Erythrobacter Species (OCh 114) and Erythrobacter longus (OCh 101)

Reversible photo-oxidation of cytochromes and reversible photobleachingof bacteriochlorophyll were observed in aerobically grown cellsof the aerobic heterotroph, the Erythrobacter species (OCh 114).Light inhibited O₂-uptake by cells of this bacterium and Erythrobacterlongus (OCh 101). A vesicular structure of intracytoplasmicmembrane systems was observed in sections of aerobically growncells of OCh 114. These bacteria may be called aerobic photosyntheticbacteria (i.e., photosynthetic bacteria which can utilize lightenergy under aerobic conditions but not under anaerobic conditions). (Received September 9, 1981; Accepted December 2, 1981)     

Control of bacteriochlorophyll accumulation by light in Rhodobacter capsulatus.

Oxygen levels which control induction of the assembly of the pigment-protein photosynthetic polypeptides in dark-grown Chloroflexus aurantiacus were determined. The induction signal by low-oxygen tension is not directly related to the respiratory competence of these photosynthetic cells. Cytochrome c554, the primary electron donor to P865+ of the reaction center, is not present in dark-grown respiratory cells but is induced in parallel with bacteriochlorophylls a and c and at similar oxygen partial pressure. The development of these components of the photosynthetic apparatus and its electron transport chain is completely independent of the presence of any detectable light or bacteriochlorophyll c or a pigments in C. aurantiacus.     

Structure of the puf operon of the obligately aerobic, bacteriochlorophyll alpha-containing bacterium Roseobacter denitrificans OCh114 and its expression in a Rhodobacter capsulatus puf puc deletion mutant.

Roseobacter denitrificans (Erythrobacter species strain OCh114) synthesizes bacteriochlorophyll a (BChl) and the photosynthetic apparatus only in the presence of oxygen and is unable to carry out primary photosynthetic reactions and to grow photosynthetically under anoxic conditions. The puf operon of R. denitrificans has the same five genes in the same order as in many photosynthetic bacteria, i.e., pufBALMC. PufC, the tetraheme subunit of the reaction center (RC), consists of 352 amino acids (Mr, 39,043); 20 and 34% of the total amino acids are identical to those of PufC of Chloroflexus aurantiacus and Rubrivivax gelatinosus, respectively. The N-terminal hydrophobic domain is probably responsible for anchoring the subunit in the membrane. Four heme-binding domains are homologous to those of PufC in several purple bacteria. Sequences similar to pufQ and pufX of Rhodobacter capsulatus were not detected on the chromosome of R. denitrificans. The puf operon of R. denitrificans was expressed in trans in Escherichia coli, and all gene products were synthesized. The Roseobacter puf operon was also expressed in R. capsulatus CK11, a puf puc double-deletion mutant. For the first time, an RC/light-harvesting complex I core complex was heterologously synthesized. The strongest expression of the R. denitrificans puf operon was observed under the control of the R. capsulatus puf promoter, in the presence of pufQ and pufX and in the absence of pufC. Charge recombination between the primary donor P+ and the primary ubiquinone Q(A)- was observed in the transconjugant, showing that the M and L subunits of the RC were correctly assembled. The transconjugants did not grow photosynthetically under anoxic conditions.     

Growth Characteristics and Substrate Specificity of Aerobic Photosynthetic Bacterium, Erythrobacter Sp. (OCh 114)

Optimal growth conditions and substrate specificity of the aerobicphotosynthetic bacterium, Erythrobacter sp. (OCh 114), wereinvestigated. Erythrobacter utilized 19 out of 26 substratestested, including several sugars and amino acids. Glycerol andlactate were the most effective as electron donors or carbonsources. Maximum growth was obtained at a salinity of about25, pH 8–9 and temperature 28°C in a glycerol-enrichedmedium. A suitable growth medium for Erythrobacter sp. (OCh114) is proposed. (Received October 18, 1985; Accepted January 10, 1986)     

Photosynthetic electron transfer system is inoperative in anaerobic cells of Erythrobacter species strain OCh 114

Some of the photosynthetic reactions were measured under aerobic and anaerobic conditions in intact cells of an aerobic photosynthetic bacterium Erythrobacter species strain OCh 114 (ATCC No. 33942). In intact cells, the flash-light induced oxidation of cytochrome c-551, the continuous light-induced oxidation of reaction center bacteriochlorophyll and the continuous light-induced pH change ( ) of the suspension decreased on aerobic-anaerobic transition and almost disappeared under anaerobic conditions. These photosynthetic reactions reappeared when the suspension was aerated again. These phenomena were reconciled with the fact that Erythrobacter sp. cannot grow anaerobically even in the light. The incompetence of photoanaerobic growth of this bacterium was explained by the reduction of the primary electron acceptor (Q_I) before illumination, resulting partly from the relatively high midpoint potential of Q_I of this bacterium.Abbreviations Q_I Primary electron acceptor - E_h ambient redox potential - E_m midpoint redox potential     

Control of nitrogenase in a photosynthetic autotrophic bacterium, Ectothiorhodospira sp.

An Ectothiorhodospira species fixed nitrogen when grown as an autotroph in completely inorganic medium by using a variety of electron donors. The organism also used organic carbon sources; however, this required induction of synthesis of various enzymes, whereas the enzymes needed for autotrophic growth were synthesized constitutively. Nitrogenase induction and function were inhibited by ammonium chloride. Nitrogenase activity was dependent on light and inhibited by oxygen.     

Composition and localization of bacteriochlorophyll a intermediates in the purple photosynthetic bacterium Rhodopseudomonas sp. Rits

Rhodopseudomonas sp. Rits is a recently isolated new species of photosynthetic bacteria and found to accumulate a significantly high amount of bacteriochlorophyll (BChl) a intermediates possessing non-, di- and tetra-hydrogenated geranylgeranyl groups at the 17-propionate as well as normal phytylated BChl a (Mizoguchi T et al. (2006) FEBS Lett 580:137-143). A phylogenetic analysis showed that this bacterium was closely related to Rhodopseudomonas palustris. The strain Rits synthesizes light-harvesting complexes 2 and 4 (LH2/4), as peripheral antennas, as well as the reaction center and light-harvesting 1 core complex (RC-LH1 core). The amounts of these complexes were dependent upon the incident light intensities, which was also a typical behavior of Rhodopseudomonas palustris. HPLC analyses of extracted pigments indicated that all four BChls a were associated with the purified photosynthetic pigment-protein, as complexes described above. The results suggested that this bacterium could use these pigments as functional molecules within the LH2/4 and RC-LH1 core. Pigment compositional analyses in several purple photosynthetic bacteria showed that such BChl a intermediates were always detected and were more widely distributed than expected. Long chains in the propionate moiety of BChl a would be one of the important factors for assembly of LH systems in purple photosynthetic bacteria.