Heterotrophic euglenid Rhabdomonas costata resembles its phototrophic relatives in many aspects of molecular and cell biology.

Euglenids represent a group of protists with diverse modes of feeding. To date, only a partial genomic sequence of Euglena gracilis and transcriptomes of several phototrophic and secondarily osmotrophic species are available, while primarily heterotrophic euglenids are seriously undersampled. In this work, we begin to fill this gap by presenting genomic and transcriptomic drafts of a primary osmotroph, Rhabdomonas costata. The current genomic assembly length of 100 Mbp is 14× smaller than that of E. gracilis. Despite being too fragmented for comprehensive gene prediction it provided fragments of the mitochondrial genome and comparison of the transcriptomic and genomic data revealed features of its introns, including several candidates for nonconventional types. A set of 39,456 putative R. costata proteins was predicted from the transcriptome. Annotation of the mitochondrial core metabolism provides the first data on the facultatively anaerobic mitochondrion of R. costata, which in most respects resembles the mitochondrion of E. gracilis with a certain level of streamlining. R. costata can synthetise thiamine by enzymes of heterogenous provenances and haem by a mitochondrial-cytoplasmic C4 pathway with enzymes orthologous to those found in E. gracilis. The low percentage of green algae-affiliated genes supports the ancestrally osmotrophic status of this species.

Draft Genome Sequence of Chromatium okenii Isolated from the Stratified Alpine Lake Cadagno.

Blooms of purple sulfur bacteria (PSB) are important drivers of the global sulfur cycling oxidizing reduced sulfur in intertidal flats and stagnant water bodies. Since the discovery of PSB Chromatium okenii in 1838, it has been found that this species is characteristic of for stratified, sulfidic environments worldwide and its autotrophic metabolism has been studied in depth since. We describe here the first high-quality draft genome of a large-celled, phototrophic, γ-proteobacteria of the genus Chromatium isolated from the stratified alpine Lake Cadagno, C. okenii strain LaCa. Long read technology was used to assemble the 3.78 Mb genome that encodes 3,016 protein-coding genes and 67 RNA genes. Our findings are discussed from an ecological perspective related to Lake Cadagno. Moreover, findings of previous studies on the phototrophic and the proposed chemoautotrophic metabolism of C. okenii were confirmed on a genomic level. We additionally compared the C. okenii genome with other genomes of sequenced, phototrophic sulfur bacteria from the same environment. We found that biological functions involved in chemotaxis, movement and S-layer-proteins were enriched in strain LaCa. We describe these features as possible adaptions of strain LaCa to rapidly changing environmental conditions within the chemocline and the protection against phage infection during blooms. The high quality draft genome of C. okenii strain LaCa thereby provides a basis for future functional research on bioconvection and phage infection dynamics of blooming PSB.

[Phylogenetic position of the purple sulfur bacterium Lamprobacter modestohalophilus determined based on the data on new strains of the species].

Lamprobacter, the genus of halophilic purple sulfur bacteria (PSB) with the single species Lpb. modestohalophilus was described in 1979. Rod-shaped Lamprobacter cells contained gas vacuoles during the nonmotile growth phase; motile cells without gas vesicles were formed sometimes. Bacteria contained bacteriochlorophyll a and a carotenoid okenone. The names of this genus and species were included in the list of approved microbial names in 1988. Since the type strain Lpb. modestohalophilus ROI(T) has been lost, its 16S rRNA gene sequences have not been obtained. Based on analysis of the 16S rRNA genes, a new genus Halochromatium comprising the motile extremely halophilic Chromatium-like species was proposed in 1998. Members of this genus never contain gas vacuoles. In spite of the phenotypic differences between the genera Lamprobacter and Halochromatium, phylogenetic boundaries between these taxa remained undetermined. Description of a marine bacteria belonging to Lamprobacter according to its morphological andphysiological properties as a new Halochromatium species, Hch. roseum, resulted in additional complication of the taxonomic situation. The present work provides evidence for the preservation of two phenotypically and phylogenetically different genera, Lamprobacter and Halochromatium, Lpb. modestohalophilus is proposed, as the type species of the genus Lamprobacter. Characteristics of two Lpb. modestohalophilus strains were extensively investigated, and one of them (strain Sivash) was proposed as the neotype strain of the species. It was suggested to retain the genus Halochromatium as containing extremely halophilic species Hch. salexigens and Hch. glycolicum, while transfer of the weakly halophilic species Hch. roseum to the genus Lamprobacter is proposed, resulting in a new combination Lamprobacter roseus comb. nov.

Investigation of the redox interaction between Mn-bicarbonate complexes and reaction centers from Rhodobacter sphaeroides R-26, Chromatium minutissimum, and Chloroflexus aurantiacus.

The change in the dark reduction rate of photooxidized reaction centers (RC) of type II from three anoxygenic bacteria (Rhodobacter sphaeroides R-26, Chromatium minutissimum, and Chloroflexus aurantiacus) having different redox potentials of the P(+)/P pair and availability of RC for exogenous electron donors was investigated upon the addition of Mn(2+) and HCO(3)(-). It was found that the dark reduction of P(870)(+) from Rb. sphaeroides R-26 is considerably accelerated upon the combined addition of 0.5 mM MnCl(2) and 30-75 mM NaHCO(3) (as a result of formation of "low-potential" complexes [Mn(HCO(3))(2)]), while MnCl(2) and NaHCO(3) added separately had no such effect. The effect is not observed either in RC from Cf. aurantiacus (probably due to the low oxidation potential of the primary electron donor, P(865), which results in thermodynamic difficulties of the redox interaction between P(865)(+) and Mn(2+)) or in RC from Ch. minutissimum (apparently due to the presence of the RC-bound cytochrome preventing the direct interaction between P(870)(+) and Mn(2+)). The absence of acceleration of the dark reduction of P(870)(+) in the RC of Rb. sphaeroides R-26 when Mn(2+) and HCO(3)(-) were replaced by Mg(2+) or Ca(2+) and by formate, oxalate, or acetate, respectively, reveals the specificity of the Mn2+-bicarbonate complexes for the redox interaction with P(+). The results of this work might be considered as experimental evidence for the hypothesis of the participation of Mn(2+) complexes in the evolutionary origin of the inorganic core of the water oxidizing complex of photosystem II.

Long-term population dynamics of phototrophic sulfur bacteria in the chemocline of Lake Cadagno, Switzerland.

Population analyses in water samples obtained from the chemocline of crenogenic, meromictic Lake Cadagno, Switzerland, in October for the years 1994 to 2003 were studied using in situ hybridization with specific probes. During this 10-year period, large shifts in abundance between purple and green sulfur bacteria and among different populations were obtained. Purple sulfur bacteria were the numerically most prominent phototrophic sulfur bacteria in samples obtained from 1994 to 2001, when they represented between 70 and 95% of the phototrophic sulfur bacteria. All populations of purple sulfur bacteria showed large fluctuations in time with populations belonging to the genus Lamprocystis being numerically much more important than those of the genera Chromatium and Thiocystis. Green sulfur bacteria were initially represented by Chlorobium phaeobacteroides but were replaced by Chlorobium clathratiforme by the end of the study. C. clathratiforme was the only green sulfur bacterium detected during the last 2 years of the analysis, when a shift in dominance from purple sulfur bacteria to green sulfur bacteria was observed in the chemocline. At this time, numbers of purple sulfur bacteria had decreased and those of green sulfur bacteria increased by about 1 order of magnitude and C. clathratiforme represented about 95% of the phototrophic sulfur bacteria. This major change in community structure in the chemocline was accompanied by changes in profiles of turbidity and photosynthetically available radiation, as well as for sulfide concentrations and light intensity. Overall, these findings suggest that a disruption of the chemocline in 2000 may have altered environmental niches and populations in subsequent years.

Reconstitution of carotenoids into the light-harvesting complex B800-850 of Chromatium minutissimum.

Chromatophores and peripheral light-harvesting complexes B800-850 with a trace of carotenoids were isolated from Chromatium minutissimum cells in which carotenoid biosynthesis was inhibited by diphenylamine. Three methods previously used for the reconstitution of carotenoids into either the light-harvesting (LH1) type complexes or reaction centers (RC) of carotenoidless mutants were examined for the possibility of carotenoid reconstitution into the carotenoid depleted chromatophores. All these methods were found to be unsuitable because carotenoid depleted complex B800-850 from Chr. minutissimum is characterized by high lability. We have developed a novel method maintaining the native structure of the complexes and allowing reconstitution of up to 80% of the carotenoids as compared to the control. The reconstituted complex has a similar CD spectrum in the carotenoid region as the control, and its structure restores its stability. These data give direct proof for the structural role of carotenoids in bacterial photosynthesis.

Mechanism and biological role of nitric oxide binding to cytochrome c'.

The binding of nitric oxide to ferric and ferrous Chromatium vinosum cytochrome c' was studied. The extinction coefficients for the ferric and ferrous nitric oxide complexes were measured. A binding model that included both a conformational change and dissociation of the dimer into subunits provided the best fit for the ferric cytochrome c' data. The NO (nitric oxide) binding affinity of the WT ferric form was found to be comparable to the affinities displayed by the ferric myoglobins and hemoglobins. Using an improved fitting model, positive cooperativity was found for the binding of NO to the WT ferric and ferrous forms, while anticooperativity was the case for the Y16F mutant. Structural explanations accounting for the binding are proposed. The NO affinity of ferrous cytochrome c' was found to be much lower than the affinities of myoglobins, hemoglobins, and pentacoordinate heme models. Structural factors accounting for the difference in affinities were analyzed. The NO affinity of ferrous cytochrome c' was found to be in the range typical of receptors and carriers. In addition, cytochrome c' was found to react with cytosolic light-irradiated membranes in the presence of succinate and carbon monoxide. With these results, a biochemical model of cytochrome c' functioning as a nitric oxide carrier was proposed.

Characterization of glutathione amide reductase from Chromatium gracile. Identification of a novel thiol peroxidase (Prx/Grx) fueled by glutathione amide redox cycling.

Among the Chromatiaceae, the glutathione derivative gamma-l-glutamyl-l-cysteinylglycine amide, or glutathione amide, was reported to be present in facultative aerobic as well as in strictly anaerobic species. The gene (garB) encoding the central enzyme in glutathione amide cycling, glutathione amide reductase (GAR), has been isolated from Chromatium gracile, and its genomic organization has been examined. The garB gene is immediately preceded by an open reading frame encoding a novel 27.5-kDa chimeric enzyme composed of one N-terminal peroxiredoxin-like domain followed by a glutaredoxin-like C terminus. The 27.5-kDa enzyme was established in vitro to be a glutathione amide-dependent peroxidase, being the first example of a prokaryotic low molecular mass thiol-dependent peroxidase. Amino acid sequence alignment of GAR with the functionally homologous glutathione and trypanothione reductases emphasizes the conservation of the catalytically important redox-active disulfide and of regions involved in binding the FAD prosthetic group and the substrates glutathione amide disulfide and NADH. By establishing Michaelis constants of 97 and 13.2 microm for glutathione amide disulfide and NADH, respectively (in contrast to K(m) values of 6.9 mm for glutathione disulfide and 1.98 mm for NADPH), the exclusive substrate specificities of GAR have been documented. Specificity for the amidated disulfide cofactor partly can be explained by the substitution of Arg-37, shown by x-ray crystallographic data of the human glutathione reductase to hydrogen-bond one of the glutathione glycyl carboxylates, by the negatively charged Glu-21. On the other hand, the preference for the unusual electron donor, to some extent, has to rely on the substitution of the basic residues Arg-218, His-219, and Arg-224, which have been shown to interact in the human enzyme with the NADPH 2'-phosphate group, by Leu-197, Glu-198, and Phe-203. We suggest GAR to be the newest member of the class I flavoprotein disulfide reductase family of oxidoreductases.

Energy transfer and charge separation in the purple non-sulfur bacterium Roseospirillum parvum.

The antenna reaction centre system of the recently described purple non-sulfur bacterium Roseospirillum parvum strain 930I was studied with various spectroscopic techniques. The bacterium contains bacteriochlorophyll (BChl) a, 20% of which was esterified with tetrahydrogeranylgeraniol. In the near-infrared, the antenna showed absorption bands at 805 and 909 nm (929 nm at 6 K). Fluorescence bands were located at 925 and 954 nm, at 300 and 6 K, respectively. Fluorescence excitation spectra and time resolved picosecond absorbance difference spectroscopy showed a nearly 100% efficient energy transfer from BChl 805 to BChl 909, with a time constant of only 2.6 ps. This and other evidence indicate that both types of BChl belong to a single LH1 complex. Flash induced difference spectra show that the primary electron donor absorbs at 886 nm, i.e. at 285 cm(-1) higher energy than the long wavelength antenna band. Nevertheless, the time constant for trapping in the reaction centre was the same as for almost all other purple bacteria: 55+/-5 ps. The shape as well as the amplitude of the absorbance difference spectrum of the excited antenna indicated exciton interaction and delocalisation of the excited state over the BChl 909 ring, whereas BChl 805 appeared to have a monomeric nature.

Analysis of the Thiocapsa pfennigii polyhydroxyalkanoate synthase: subcloning, molecular characterization and generation of hybrid synthases with the corresponding Chromatium vinosum enzyme.

The PHA synthase structural gene of Thiocapsa pfennigii was identified and subcloned on a 2.8-kbp BamHI restriction fragment, which was cloned recently from a genomic 15.6-kbp EcoRI restriction fragment. Nucleotide sequence analysis of this fragment revealed three open reading frames (ORFs), representing coding regions. Two ORFs encoded for the PhaE (Mr 40,950) and PhaC (Mr 40,190) subunits of the PHA synthase from T. pfennigii and exhibited high homology with the corresponding proteins of the Chromatium vinosum (52.8% and 85.2% amino acid identity) and the Thiocystis violacea (52.5% and 82.4%) PHA synthases, respectively. This confirmed that the T. pfennigii PHA synthase was composed of two different subunits. Also, with respect to the molecular organization of phaE and phaC, this region of the T. pfennigii genome resembled very much the corresponding regions of C. vinosum and of Thiocystis violacea. A recombinant strain of Pseudomonas putida, which overexpressed phaE and phaC from T. pfennigii, was used to isolate the PHA synthase by a two-step procedure including chromatography on Procion Blue H-ERD and hydroxyapatite. The isolated PHA synthase consisted of two proteins exhibiting the molecular weights predicted for PhaE and PhaC. Hybrid PHA synthases composed of PhaE from T. pfennigii and PhaC from C. vinosum and vice versa were constructed and functionally expressed in a PHA-negative mutant of P. putida; and the resulting PHAs were analyzed.

Complex formation between Chromatium vinosum ferric cytochrome c' and bromophenol blue.

An unusual complex has been observed between the common electrophoresis tracer bromophenol blue (BPB) and the cytochrome c' from Chromatium vinosum during polyacrylamide gel electrophoresis. Complex formation results in a shift and increase in the intensity of the visible absorption band of BPB. Differential spectrophotometric titration of BPB with cytochrome c' indicates that one BPB binds to each of the two subunits of cytochrome c' with a binding constant of 4.2(0.5) x 10(5). The absence of a significant effect of ionic strength on the binding constant and the effect of Triton X-100 on the spectrum of BPB suggest that hydrophobic interactions are important to binding. An analysis of the structure of C. vinosum cytochrome c' shows the presence of a surface hydrophobic patch which may participate in the binding interaction. Many of the hydrophobic amino acids in the patch are well conserved by type among all known sequences of cytochrome c' and are found in loop elements of the 3D structure, suggesting a functional basis for conservation. It is proposed that the binding of BPB may mimic a relevant interaction involving the cytochrome c' biological function.

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.

Sirohaem sulfite reductase and other proteins encoded by genes at the dsr locus of Chromatium vinosum are involved in the oxidation of intracellular sulfur.

The sequence of the dsr gene region of the phototrophic sulfur bacterium Chromatium vinosum D (DSMZ 180) was determined to clarify the in vivo role of 'reverse' sirohaem sulfite reductase. The dsrAB genes encoding dissimilatory sulfite reductase are part of a gene cluster, dsrABEFHCMK, that encodes four small, soluble proteins (DsrE, DsrF, DsrH and DsrC), a transmembrane protein (DsrM) with similarity to haem-b-binding polypeptides and a soluble protein (DsrK) resembling [4Fe-4S]-cluster-containing heterodisulfide reductase from methanogenic archaea. Northern hybridizations showed that expression of the dsr genes is increased by the presence of reduced sulfur compounds. The dsr genes are not only transcribed from a putative promoter upstream of dsrA but primary transcripts originating from (a) transcription start site(s) downstream of dsrB are also formed. Polar insertion mutations immediately upstream of dsrA, and in dsrB, dsrH and dsrM, led to an inability of the cells to oxidize intracellularly stored sulfur. The capability of the mutants to oxidize sulfide, thiosulfate and sulfite under photolithoautotrophic conditions was unaltered. Photoorganoheterotrophic growth was also unaffected. 'Reverse' sulfite reductase and DsrEFHCMK are, therefore, not essential for oxidation of sulfide or thiosulfate, but are obligatory for sulfur oxidation. These results, together with the finding that the sulfur globules of C. vinosum are located in the extracytoplasmic space whilst the dsr gene products appear to be either cytoplasmic or membrane-bound led to the proposal of new models for the pathway of sulfur oxidation in this phototrophic sulfur bacterium.

Evidence against the double-arginine motif as the only determinant for protein translocation by a novel Sec-independent pathway in Escherichia coli.

Proteins which are synthesized with a signal peptide containing a 'double-arginine' motif may be translocated across the bacterial cytoplasmic membrane by a mechanism that is different from the known Sec and signal recognition particle pathways. The function of the double-arginine motif as a determinant for this novel pathway was studied by expressions of gene constructs coding for the high potential iron-sulfur protein (HiPIP) from Chromatium vinosum D in Escherichia coli. When the protein was produced with its original double-arginine motif-containing signal peptide, it was in part translocated into the periplasm and thereby processed, as shown by immunoblots after cell fractionation and N-terminal sequencing of purified HiPIP. Processing was not inhibited significantly by 3 mM sodium azide, indicating that translocation of HiPIP occurs by a SecA-independent pathway. Translocation of HiPIP could be altered to the SecA-dependent mode when its signal peptide was substituted by that of PelB from Erwinia carotovora. When the HiPIP double-arginine motif (SRRDAVK) was introduced into the corresponding position of the PelB signal peptide, the transport pathway remained SecA-dependent. This indicates that additional determinants are required for translocation by the Sec-independent pathway.

Synechocystis sp. PCC6803 possesses a two-component polyhydroxyalkanoic acid synthase similar to that of anoxygenic purple sulfur bacteria.

During cultivation under storage conditions with BG11 medium containing acetate as a carbon source, Synechocystis sp. PCC6803 accumulated poly(3-hydroxybutyrate) up to 10% (w/w) of the cell dry weight. Our analysis of the complete Synechocystis sp. PCC6803 genome sequence, which had recently become available, revealed that not only the open reading frame slr1830 (which was designated as phaC) but also the open reading frame slr1829, which is located colinear and upstream of phaC, most probably represent a polyhydroxyalkanoic acid (PHA) synthase gene. The open reading frame slr1829 was therefore designated as phaE. The phaE and phaC gene products exhibited striking sequence similarities to the corresponding PHA synthase subunits PhaE and PhaC of Thiocystis violacea, Chromatium vinosum, and Thiocapsa pfennigii. The Synechocystis sp. PCC6803 genes were cloned using PCR and were heterologously expressed in Escherichia coli and in Alcaligenes eutrophus. Only coexpression of phaE and phaC partially restored the ability to accumulate poly(3-hydroxybutyrate) in the PHA-negative mutant A. eutrophus PHB-4. These results confirmed our hypothesis that coexpression of the two genes is necessary for the synthesis of a functionally active Synechocystis sp. PCC6803 PHA synthase. PHA granules were detected by electron microscopy in these cells, and the PHA-granule-associated proteins were studied. Western blot analysis of Synechocystis sp. PCC6803 crude cellular extracts and of granule-associated proteins employing antibodies raised against the PHA synthases of A. eutrophus (PhaC) and of C. vinosum (PhaE and PhaC) revealed no immunoreaction.

Sulfide oxidation in the phototrophic sulfur bacterium Chromatium vinosum.

Sulfide oxidation in the phototrophic purple sulfur bacterium Chromatium vinosum D (DSMZ 180(T)) was studied by insertional inactivation of the fccAB genes, which encode flavocytochrome c, a protein that exhibits sulfide dehydrogenase activity in vitro. Flavocytochrome c is located in the periplasmic space as shown by a PhoA fusion to the signal peptide of the hemoprotein subunit. The genotype of the flavocytochrome-c-deficient Chr. vinosum strain FD1 was verified by Southern hybridization and PCR, and the absence of flavocytochrome c in the mutant was proven at the protein level. The oxidation of thiosulfate and intracellular sulfur by the flavocytochrome-c-deficient mutant was comparable to that of the wild-type. Disruption of the fccAB genes did not have any significant effect on the sulfide-oxidizing ability of the cells, showing that flavocytochrome c is not essential for oxidation of sulfide to intracellular sulfur and indicating the presence of a distinct sulfide-oxidizing system. In accordance with these results, Chr. vinosum extracts catalyzed electron transfer from sulfide to externally added duroquinone, indicating the presence of the enzyme sulfide:quinone oxidoreductase (EC 1.8.5.-). Further investigations showed that the sulfide:quinone oxidoreductase activity was sensitive to heat and to quinone analogue inhibitors. The enzyme is strictly membrane-bound and is constitutively expressed. The presence of sulfide:quinone oxidoreductase points to a connection of sulfide oxidation to the membrane electron transport system at the level of the quinone pool in Chr. vinosum.

Molecular genetic evidence for extracytoplasmic localization of sulfur globules in Chromatium vinosum.

Purple sulfur bacteria store sulfur as intracellular globules enclosed by a protein envelope. We cloned the genes sgpA, sgpB, and sgpC, which encode the three different proteins that constitute the sulfur globule envelope of Chromatium vinosum D (DSMZ 180(T)). Southern hybridization analyses and nucleotide sequencing showed that these three genes are not clustered in the same operon. All three genes are preceded by sequences resembling sigma70-dependent promoters, and hairpin structures typical for rho-independent terminators are found immediately downstream of the translational stop codons of sgpA, sgpB, and sgpC. Insertional inactivation of sgpA in Chr. vinosum showed that the presence of only one of the homologous proteins SgpA and SgpB suffices for formation of intact sulfur globules. All three sgp genes encode translation products which - when compared to the isolated proteins - carry amino-terminal extensions. These extensions meet all requirements for typical signal peptides indicating an extracytoplasmic localization of the sulfur globule proteins. A fusion of the phoA gene to the sequence encoding the proposed signal peptide of sgpA led to high specific alkaline phosphatase activities in Escherichia coli, further supporting the envisaged targeting process. Together with electron microscopic evidence these results provide strong indication for an extracytoplasmic localization of the sulfur globules in Chr. vinosum and probably in other Chromatiaceae. Extracytoplasmic formation of stored sulfur could contribute to the transmembranous Deltap that drives ATP synthesis and reverse electron flow in Chr. vinosum.

Towards the phylogeny of APS reductases and sirohaem sulfite reductases in sulfate-reducing and sulfur-oxidizing prokaryotes.

The genes for adenosine-5'-phosphosulfate (APS) reductase, aprBA, and sirohaem sulfite reductase, dsrAB, from the sulfur-oxidizing phototrophic bacterium Chromatium vinosum strain D (DSMZ 180(T)) were cloned and sequenced. Statistically significant sequence similarities and similar physicochemical properties suggest that the aprBA and dsrAB gene products from Chr. vinosum are true homologues of their counterparts from the sulfate-reducing chemotrophic archaeon Archaeoglobus fulgidus and the sulfate-reducing chemotrophic bacterium Desulfovibrio vulgaris. Evidence for the proposed duplication of a common ancestor of the dsrAB genes is provided. Phylogenetic analyses revealed a greater evolutionary distance between the enzymes from Chr. vinosum and D. vulgaris than between those from A. fulgidus and D. vulgaris. The data reported in this study are most consistent with the concept of common ancestral protogenotic genes both for dissimilatory sirohaem sulfite reductases and for APS reductases. The aprA gene was demonstrated to be a suitable DNA probe for the identification of apr genes from organisms of different phylogenetic positions. PCR primers and conditions for the amplification of apr homologous regions are described.

Cloning and sequencing of the gene encoding the high potential iron-sulfur protein (HiPIP) from the purple sulfur bacterium Chromatium vinosum.

The gene encoding the high potential iron-sulfur protein (HiPIP) of Chromatium vinosum strain D (DSM 180T) was cloned from an EcoRI-HindIII digest of genomic DNA. A nucleotide sequence of 648 bp length was determined which contained the coding region and putative promoter and termination sites. The gene codes for a 122 residue 12761 Da protein. The C-terminal 85 residues are those of the previously biochemically determined sequence, whereas the N-terminal 37 residues constitute a leader peptide which shows characteristics of the double arginine signal sequences of complex cofactor containing periplasmic proteins.

Insertional gene inactivation in a phototrophic sulphur bacterium: APS-reductase-deficient mutants of Chromatium vinosum.

In purple sulphur bacteria of the family Chromatiaceae sulphite oxidation via intermediary formation of adenylylsulphate is an enzymologically well characterized process. In contrast, the role of an alternative direct oxidation pathway via the enzyme sulphite:acceptor oxidoreductase has not been resolved. This paper reports the cloning of the genes encoding the adenylylsulphate-forming enzyme adenosine-5'-phosphosulphate (APS) reductase from Chromatium vinosum strain D (DSM 180'), a representative of the purple sulphur bacteria, and the construction of mutations in these genes by insertion of a kanamycin omega cartridge. The mutated genes were transferred to C. vinosum on suicide vectors of the pSUP series by conjugation and delivered to the chromosome by double homologous recombination. Southern hybridization and PCR analyses of the recombinants obtained verified the first insertional gene inactivation in purple sulphur bacteria. Enzymological studies demonstrated the absence of APS reductase from the mutants. Further phenotypic characterization showed no significant effect of APS reductase deficiency on the sulphite-oxidizing ability of the cells under photolithoautotrophic growth conditions. In the wild-type as well as in mutant strains, tungstate, the specific antagonist of molybdate, led to the intermediary accumulation of sulphite in the medium during sulphide oxidation and strongly inhibited growth with sulphite as photosynthetic electron donor; this indicates that a molybdoenzyme, probably sulphite:acceptor oxidoreductase, is the main sulphite-oxidizing enzyme in C. vinosum. Specific inactivation of selected genes as developed for C. vinosum in this study provides a powerful genetic tool for further analysis of sulphur metabolism and other metabolic pathways in phototrophic sulphur bacteria.