Photosynthetic Purple Sulfur Bacterium Research Articles

Mono- and bicyclic squalene derivatives as potential proxies for anaerobic photosynthesis in lacustrine sulfur-rich sediments

Two novel triterpenoid biomarkers have been isolated from a recent anoxic sulfur-rich sediment (Lake Cadagno, Switzerland) and identified by NMR as 11,15-dihydro-Δ 13,10(14)-cyclosqualene 1 and bis-(6,11-cyclofarnesa-2,7(14)-diene) 2. Both compounds have a novel hydrocarbon skeleton not known thus far in living organisms and formed by cyclization of squalene, likely through an enzymatic process. Regarding their origin, the 13C-depleted values of their stable carbon isotopic composition suggest a derivation either from purple sulfur photosynthetic bacteria or from anaerobic heterotrophic organisms feeding on the 13C-depleted biomass fixed by photosynthetic bacteria. Therefore, these novel triterpenoids may represent potential proxies for photic zone anoxia in lacustrine settings.

An unusual arrangement of pur and lpx genes in the photosynthetic purple sulfur bacterium Allochromatium vinosum.

The nucleotide sequence of a 1634 bp DNA fragment from the photosynthetic purple sulfur bacterium Allochromatium vinosum contains one complete and two partial open reading frames. Sequence comparisons to genes from other organisms suggest that this A. vinosum DNA fragment contains, starting from the 5' end, the following: (1) 234 bp at the 3' end of the A. vinosum purH gene, coding for 78 amino acids at the C-terminus of the bi-functional 5'-phosphoribosyl-5-aminoimidazole-4-carboxamide formyltransferase/IMP cyclohydrolase (EC 2.1.2.3), an enzyme involved in de novo purine biosynthesis; (2) 777 bp of the A. vinosum lpxA gene, coding for all 259 amino acids of the UDP-N-acetylglucosamine-O-acyltransferase, an enzyme involved in lipid A biosynthesis; and (3) 567 bp at the 5' end of the A. vinosum purD gene, coding for 189 amino acids at the N-terminus of 5'-phosphoribosyl glycinamide synthetase (EC 6.3.4.13), a second enzyme involved in de novo purine biosynthesis. The presence of a gene coding for an enzyme involved in lipid A biosynthesis between two genes coding for enzymes of the de novo purine biosynthesis pathway represents a unique arrangement of these genes.

Genes encoding light-harvesting and reaction center proteins from Chromatium vinosum

Sequencing of a 3.4 kb DNA fragment isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum and of PCR products has resulted in identification of the Chr. vinosum pufL, pufM, and pufC genes, reading from the 5′ to the 3′ direction, and coding, respectively, for the L, M and cytochrome c subunits of the reaction center of this bacterium. Other PCR products have been used to obtain complete sequences for the pufB and pufA genes, located immediately upstream from pufL and encoding the apoproteins of two Chr. vinosum light- harvesting proteins. The 3′-portion of the bchZ gene, a gene that codes for a protein involved in the biosynthesis of bacteriochlorophyll, has been located immediately upstream from pufB. A second pufB gene, pufB2, has been located downstream from pufC, as has the 5′-portion of a second pufA gene, pufA2. The location of a second set of pufB and pufA genes, encoding light- harvesting proteins, downstream from pufC has not previously been reported for any photosynthetic bacterium. Translation of the gene sequences encoding these Chr. vinosum light-harvesting proteins reveals both similarities to and differences from the amino acid sequences, obtained from direct sequencing of the apoproteins, previously reported for Chr. vinosum light-harvesting proteins. Translation of these gene sequences, and of those for pufL, pufM and pufC, revealed significant homology, at the amino acid level, to the corresponding peptides of photosynthetic purple non-sulfur bacteria.

Unusual organization of the genes coding for HydSL, the stable [NiFe]hydrogenase in the photosynthetic bacterium Thiocapsa roseopersicina BBS.

The characterization of a hyd gene cluster encoding the stable, bidirectional [NiFe]hydrogenase 1 enzyme in Thiocapsa roseopersicina BBS, a purple sulfur photosynthetic bacterium belonging to the family Chromatiaceae, is presented. The heterodimeric hydrogenase 1 had been purified to homogeneity and thoroughly characterized (K. L. Kovacs et al., J. Biol. Chem. 266:947-951, 1991; C. Bagyinka et al., J. Am. Chem. Soc. 115:3567-3585, 1993). As an unusual feature, a 1,979-bp intergenic sequence (IS) separates the structural genes hydS and hydL, which encode the small and the large subunits, respectively. This IS harbors two sequential open reading frames (ORFs) which may code for electron transfer proteins ISP1 and ISP2. ISP1 and ISP2 are homologous to ORF5 and ORF6 in the hmc operon, coding for a transmembrane electron transfer complex in Desulfovibrio vulgaris. Other accessory proteins are not found immediately downstream or upstream of hydSL. A hup gene cluster coding for a typical hydrogen uptake [NiFe]hydrogenase in T. roseopersicina was reported earlier (A. Colbeau et al. Gene 140:25-31, 1994). The deduced amino acid sequences of the two small (hupS and hydS) and large subunit (hupL and hydL) sequences share 46 and 58% identity, respectively. The hup and hyd genes differ in the arrangement of accessory genes, and the genes encoding the two enzymes are located at least 15 kb apart on the chromosome. Both hydrogenases are associated with the photosynthetic membrane. A stable and an unstable hydrogenase activity can be detected in cells grown under nitrogen-fixing conditions; the latter activity is missing in cells supplied with ammonia as the nitrogen source. The apparently constitutive and stable activity corresponds to hydrogenase 1, coded by hydSL, and the inducible and unstable second hydrogenase may be the product of the hup gene cluster.

12] Chaperonin 6014 and co-chaperonin 107 from Chromatium vinosum

Publisher Summary Chaperonins are a specialized class of proteins that promote assembly, disassembly, or translocation of other proteins in an ATP-dependent reaction. The heat shock proteins, chaperonin 60 (Cpn60) and chaperonin 10 (Cpnl0) from Escherichia coli, previously designated as GroEL and GroES, respectively, are classic representatives of the molecular chaperone family. Chaperonins 60 and 10 are ubiquitous in nature as similar proteins have been identified in a wide variety of prokaryotes and organelles, such as the peroxisome, chloroplast, mitochondrion, Golgi apparatus, and endoplasmic reticulum. In regard to their native structure, Cpn60 generally comprises 14 identical 60-kDa subunits arranged in a double-layered structure with a seven-fold symmetry. However, Cpnl0 is a seven-subunit homo-oligomer with a subunit molecular mass of 10 kDa. The evidence that Cpn60 and Cpnl0 interact functionally with each other has been strongly supported by both genetic and biochemical approaches. Cpn60 and Cpnl0 homologs are identified in Chromatium vinosum, an oxygenic photosynthetic purple sulfur bacterium. The data indicate that Cpn60 and Cpnl0 from C. vinosum resemble, structurally and functionally, their counterparts from E. coli. The presence of Cpn60 and ribulose-bisphosphate carboxylase/oxygenase (Rubisco) in the crude extracts of C. vinosum, grown photoheterotrophically, may be quantified by enzyme-linked immunosorbent assay (ELISA), using the “sandwich method” according to established protocols.

Novel aromatic carotenoid derivatives from sulfur photosynthetic bacteria in sediments

Novel aromatic carotenoid derivatives 7 and 8 have been identified by synthesis of reference compounds in a H 2/PtO 2-hydrogenated fraction from the organic extract of a lake sediment (lake Cadagno, Switzerland). They derive from unreported carotenoids presumably biosynthesized by purple sulfur photosynthetic bacteria ( Chromatiaceae) and represent potential biomarkers to establish the occurrence of photic zone anoxia in ancient ecosystems.

Energy Transfer and Exciton Coupling in Isolated B800−850 Complexes of the Photosynthetic Purple Sulfur BacteriumChromatium tepidum. The Effect of Structural Symmetry on Bacteriochlorophyll Excited States

Energy transfer and exciton coupling in isolated B800−850 complexes from the purple sulfur bacterium Chromatium tepidum were studied by means of spectrally resolved absorbance difference spectroscopy with a time resolution of 200 fs. Energy transfer from bacteriochlorophyll (BChl) 800 to BChl 850 was found to occur with a time constant of 0.8−0.9 ps. Remarkably, the amplitude of the absorbance changes of BChl 850 was 4 times larger than that of BChl 800. By relating this result to the crystal structure of B800−850 complexes of Rhodopseudomonas acidophila (MacDermott, G.; Prince, S. M.; Freer, A. A.; Hawthornthwaite-Lawless, A. M.; Papiz, M. Z.; Cogdell, R. J.; Isaacs; N. W. Nature 1995, 374, 517), it was concluded that the spectral properties of BChl 850 are mainly determined by strong exciton interactions between BChl 850 molecules in a circular symmetric arrangement, which lead to concentration of the oscillator strength in a few optically allowed transitions, corresponding to delocalized eigenstates. I...

Characterization of Flavocytochrome c552 from the Thermophilic Photosynthetic Bacterium Chromatium tepidum

A M r 68 kDa flavocytochrome c 552 has been isolated from the thermophilic photosynthetic purple sulfur bacterium Chromatium tepidum and shown to consist of a M r 25 kDa subunit that contains two covalently bound heme c and a M r 43 kDa subunit that probably contains a single FAD. The prosthetic group content, absorbance spectra, and subunit composition of the C. tepidum flavocytochrome are quite similar to those previously reported for the flavocytochrome c 552 isolated from a mesophilic Chromatium species, Chromatium vinosum. The oxidation-reduction properties of the hemes present in the C. tepidum flavocytochrome have been characterized by titrations, the effect of temperature on the catalytic activity of the protein has been investigated, and the heme environment has been characterized using resonance Raman spectroscopy.

Spectroscopic characterization of flavocytochrome c-552 from the photosynthetic purple sulfur bacterium Chromatium vinosum

The identities of the axial ligands to the two hemes of the flavocytochrome c-552 isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum have been investigated by visible / near-infrared absorption and magnetic circular dichroism (MCD) spectroscopies, with parallel electron paramagnetic resonance (EPR) studies. One of the hemes has histidine and methionine as axial ligands and has a local environment that is relatively insensitive to the composition of the bulk medium. The second heme, the local environment of which is sensitive to changes in the composition of the bulk medium, exists as a mixture of two forms, only one of which has histidine / methionine axial ligation. One the basis of its EPR characteristics, the other form most likely has histidine / lysine axial ligation. In aqueous solution near neutral pH, more than half of the second heme is present as the histidine / lysine form, while in 50:50 water / ethylene glycol the histidine / methionine form is the dominant one.

Cloning and sequences of the structural ( hupSLC) and accessory ( hupDHI) genes for hydrogenase biosynthesis in Thiocapsa roseopersicina

The first molecular biology study on the purple sulfur photosynthetic bacterium Thiocapsa roseopersicina is reported, namely, the construction of cosmid libraries and isolation of a hydrogenase gene cluster by hybridization with hydrogenase structural genes from the purple non-sulfur bacterium, Rhodobacter capsulatus. The sequenced gene cluster contains six open reading frames, the products of which show significant degrees of identity (from 40 to 78%) with hydrogenase gene products necessary for biosynthesis of the group-I of [NiFe]hydrogenases. The structural hupSLC genes encode the small and large hydrogenase subunits and a hydrophobic protein shown to accept electrons from hydrogenase in R. capsulatus. They are followed downstream by three genes, hupDHI, which are similar to hydrogenase accessory genes found in other bacteria.

The ubiquinol:cytochrome [formula omitted] oxidoreductase of Chromatium vinosum

Chromatophore membranes isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum exhibit a quinol:cytochrome c 2( c) oxidoreductase activity that is sensitive to two specific inhibitors of cytochrome bc 1 complexes, antimycin A and myxothiazol. Digests of C. vinosum DNA hybridize to probes constructed from portions of the pet(fbc) operons that code for the cytochrome bc 1 complexes of the photosynthetic purple non-sulfur bacteria Rhodobacter capsulatus, Rhodobacter sphaeroides and Rhodospirillum rubrum. Despite the fact that it has not yet proven possible to isolate a detergent-solubilized, purified cytochrome bc 1 complex from C. vinosum, these new results, when combined with spectroscopic and kinetic data available from the literature, indicate that this purple sulfur bacterium contains a cytochrome bc 1 complex similar in structure to the well-characterized complexes found in purple non-sulfur bacteria. Equine cytochrome c and cytochromes c 2 isolated from the purple non-sulfur bacteria Rhodospirillum rubrum and Rhodopseudomonas viridis all function as effective electron acceptors from the C. vinosum cytochrome bc 1 complex. In contrast, HiPIP (high-potential iron protein) isolated from two purple sulfur bacteria, C. vinosum and Chromatium tepidum, are reduced only at low rates by quinol in the presence of C. vinosum membranes and their reduction is not inhibited by either antimycin A or myxothiazol. These observations support the hypothesis that a protein structurally related to cytochrome c 2, rather than HiPIP, is the physiological electron acceptor for the C. vinosum cytochrome bc 1 complex. Although it has not yet proven possible to purify the putative C. vinosum cytochrome c 2 to homogeneity, we report here that digests of C. vinosum DNA hybridize with probes constructed from portions of the cycA genes coding for cytochromes c 2 from Rb. capsulatus, Rps. viridis and Rb. sphaeroides. These DNA hybridization results provide further support for the hypothesis that a cytochrome c 2-like protein is present in C. vinosum.

Sequence and expression of genes encoding the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase from Chromatium vinosum

A DNA fragment bearing genes for the large ( rbcL) and small ( rbcS) subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was cloned from the photosynthetic purple sulfur bacterium Chromatium vinosum. Enzymatically fully active RuBisCO was synthesized in Escherichia coli cells when the cloned DNA was placed downstream of tac promoter. Nucleotide (nt) sequences of rbcL-rbcS were more homologous to cyanobacterial counterparts than to those from Alcaligenes eutrophus or higher plants. However, the amino acid (aa) sequence in a domain responsible for CO 2 activation in the C. vinosum rbcL product resembled the corresponding aa sequence in higher plant RuBisCOs, but not in the cyanobacterial enzymes. Chemically determined aa sequences at the N terminals of both subunits of RuBisCO purified from C. vinosum were not identical to those deduced from the nt sequences, although they were completely the same as aa sequences deduced from rbcA-rbcB, another locus encoding RuBisCO in C. vinosum. Therefore, the rbcL-rbcS locus seems to be barely expressed under a standard condition for photoautotrophic growth. The homology of the nt sequences between rbcL-and rbcA was 82%, and that between rbcS and rbcB was 63 %, whereas the codon usages of these genes were basically identical. The rbcL-rbcS and rbcA-rbcB loci therefore must have evolved from a common ancestral set of genes after duplication, instead of lateral gene transfer.

Magnetic Circular Dichroism and Linear Dichroism for Elucidation of Electronic Transitions and Their Orientations in a Reaction Center Isolated from a Thermophilic Purple Sulfur Photosynthetic Bacterium Chromatium tepidum

Abstract Electronic transitions and orientations of pigments in reaction center complex isolated from a purple sulfur bacterium Chromatium tepidum were determined by magnetic circular dichroism and linear dichroism. They are very similar to those of non-sulfur purple bacteria, indicating a convergent nature of this complex in the photosynthetic organisms.

Distinct properties of Escherichia coli products of plant-type ribulose-1,5-bisphosphate carboxylase/oxygenase directed by two sets of genes from the photosynthetic bacterium Chromatium vinosum.

We have recently described the existence of two sets of genes encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rbu-P2 carboxylase), rbcA-rbcB and rbcL-rbcS, in the photosynthetic purple sulfur bacterium Chromatium vinosum (Viale, A.M., Kobayashi, H., and Akazawa, T. (1989) J. Bacteriol. 171, 2391-2400). These genes were cloned in plasmid vectors, and their expression was studied in Escherichia coli. Expression of rbcA-rbcB in E. coli was obtained under the control of its own promoter. On the other hand, expression of rbcL-rbcS in this host was not observed unless these genes were cloned under the control of the tac promoter. Purified rbcA-rbcB and rbcL-rbcS products from E. coli consisted of large and small subunits in equimolar ratios. They also showed very close elution profiles to Rbu-P2 carboxylase isolated from C. vinosum in size-exclusion chromatography columns, thus suggesting hexadecameric (L8S8) structures. Vmax of Rbu-P2 carboxylase were very similar for both enzymes, but the Km values for CO2 and ribulose 1,5-bisphosphate showed some differences. Immunochemical and N-terminal amino acid sequence analyses of the large and small subunits encoded by rbcA-rbcB and rbcL-rbcS also differed, especially at the level of the small subunits. The comparisons described above as well as the analysis of C. vinosum crude extracts by anion-exchange chromatography indicated that Rbu-P2 carboxylase encoded by rbcA-rbcB was the only species detected in the photosynthetic bacterium.

Transcriptional regulation of genes for plant-type ribulose-1,5-bisphosphate carboxylase/oxygenase in the photosynthetic bacterium, Chromatium vinosum.

The content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the photosynthetic purple sulfur bacterium, Chromatium vinosum, grown either heterotrophically or autotrophically, was highly correlated with the level of 2.0-kb mRNA encoding genes for both large (rbcL) and small (rbcS) subunits. This result indicates the transcriptional regulation of Rubisco biosynthesis in Chromatium cells. In the analysis of transcripts for rbcL and rbcS in Escherichia coli transformed by a plasmid bearing both genes downstream of E. coli tac promoter (pCKS1), the mRNAs were found to be the same sizes as those from Chromatium. However, we were unable to detect mRNA for Rubisco in E. coli harboring a plasmid containing the genes for Rubisco and its own promoter without any E. coli promoters (pCUB1). In the in vitro transcription experiment of pCKS1 and pCUB1 by E. coli RNA polymerase, it was observed that the enzyme could not recognize the Rubisco promoter. Therefore, we have purified RNA polymerase from Chromatium cells and developed a homologous in vitro transcription system. We have detected factor(s) for transcriptional regulation from either heterotrophically or autotrophically grown cells of Chromatium using the homologous in vitro transcription system.

Spectroscopic and ligand-binding properties of an oxygen-binding heme protein from Chromatium vinosum

Magnetic circular dichroism spectra were obtained for the oxidized and reduced forms of cyanide, azide and carbon monoxide complexes of an O 2-binding hemeprotein isolated from the photosynthetic purple sulfur bacterium, Chronatium vinosum. Cyanide binding to the protein, which results in formation of a low-spin complex, was highly pH dependent with little complex formation observed at pH values near or below 7.

Lysine and arginine transport in the photosynthetic bacterium Chromatium vinosum

The photosynthetic purple sulfur bacterium Chromatium vinosum can take up both arginine and lysine in the light and, to a lesser extent, in the dark. Competitive inhibition experiments suggest the likely presence of two transport systems in this bacterium: One capable of transporting either lysine or arginine and a second capable of transporting arginine but not lysine. Uptake of both amino acids is electrogenic and appears to involve the cotransport of neither protons nor sodium ions. It is suggested that the transport occurs via an electrogenic uniport.

Properties of the reaction center of the thermophilic purple photosynthetic bacterium Chromatium tepidum

Reaction centers were purified from the thermophilic purple sulfur photosynthetic bacterium Chromatium tepidum. The reaction center consists of four polypeptides L, M, H and C, whose apparent molecular masses were determined to be 25, 30, 34 and 44 kDa, respectively, by polyacrylamide gel electrophoresis. The heaviest peptide corresponds to tightly bound cytochrome. The tightly bound cytochrome c contains two types of heme, high-potential c-556 and low-potential c-553. The low-potential heme is able to be photooxidized at 77 K. The reaction center exhibits laser-flash-induced absorption changes and circular dichroism spectra similar to those observed in other purple photosynthetic bacteria. Whole cells contain both ubiquinone and menaquinone. Reaction centers contain only a single active quinone; chemical analysis showed this to be menaquinone. Reaction center complexes without the tightly bound cytochrome were also prepared. The near-infrared pigment absorption bands are red-shifted in reaction centers with cytochrome compared to those without cytochrome.

Spectroscopic and kinetic properties of an oxygen-binding heme protein from Chromatium vinosum.

Resonance Raman and electron paramagnetic resonance spectroscopy have been utilized to identify histidine as an axial heme ligand in a high spin, heme c-containing protein isolated from the photosynthetic purple sulfur bacterium Chromatium vinosum. Resonance Raman spectroscopy has also been used to characterize the CO adduct of the C. vinosum hemoprotein. Resonance Raman spectra of the heme site obtained within 10 ns of CO photolysis from the ferrous hemoprotein are virtually identical to those of the unligated protein, indicating that there is little or no rearrangement of the heme pocket in response to ligand photolysis. The equilibrium constant for CO binding to the ferrous hemeprotein was measured to be 1.7 X 10(-5) M-1 and the CO association rate constant determined to be 5.4 X 10(3) M-1 S-1. The quantum efficiency for photodissociation of the hemoprotein X CO complex was greater than or equal to 0.9.

Role of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase in the activation process

The large (A) and small (B) subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) from the cyanobacterium Aphanothece halophytica and from the purple sulfur photosynthetic bacterium Chromatium vinosum (strain D) were separated by sucrose density gradient centrifugation at low ionic strength and alkaline pH (9.3), respectively. It was found that subunit B enhances the extent of activation by CO 2 and Mg 2+ at equilibrium of the two homologous enzymes consisting of Aphanothece large subunit and its own small subunit (A aB a) and the Chromatium large subunit and its own small subunit (A cB c). The extent of activation induced by saturating amounts of subunit B was larger with A cB c than A aB a, amounting to 3.7- and 1.8-fold of that by each catalytic core alone, respectively. Subunit B stimulated both the extent of activation at equilibrium and catalysis in a parallel and simultaneous manner with respect to the concentration of B in both homologous enzymes. These results suggest that subunit B interacts with both activation and catalytic sites simultaneously. On the other hand, Chromatium subunit B only slightly stimulated the extent of activation in the hybrid enzyme A aB c. The role of subunit B in enhancing the extent of activation at equilibrium can be substituted by the effect exerted by 6-phosphogluconate. Both homologous enzymes A aB a and A cB c showed a faster deactivation rate when the enzyme was activated in the absence of subunit B. The mechanism by which subunit B promotes activation seems to involve its effect on stabilizing the activated enzyme molecule. From studies on the K m for substrate CO 2 in the hybrid enzyme A aB c a major involvement of subunit B in influencing K m (CO 2) seems unlikely.