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  • Artikel  (18)
  • Springer  (12)
  • Blackwell Science Ltd  (5)
  • Blackwell Science Ltd, UK  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Molecular analysis of dimethyl sulphide dehydrogenase from Rhodovulum sulfidophilum: its place in the dimethyl sulphoxide reductase family of microbial molybdopterin-containing enzymes (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 44 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Dimethyl sulphide dehydrogenase catalyses the oxidation of dimethyl sulphide to dimethyl sulphoxide (DMSO) during photoautotrophic growth of Rhodovulum sulfidophilum. Dimethyl sulphide dehydrogenase was shown to contain bis(molybdopterin guanine dinucleotide)Mo, the form of the pterin molybdenum cofactor unique to enzymes of the DMSO reductase family. Sequence analysis of the ddh gene cluster showed that the ddhA gene encodes a polypeptide with highest sequence similarity to the molybdop-terin-containing subunits of selenate reductase, ethylbenzene dehydrogenase. These polypeptides form a distinct clade within the DMSO reductase family. Further sequence analysis of the ddh gene cluster identified three genes, ddhB, ddhD and ddhC. DdhB showed sequence homology to NarH, suggesting that it contains multiple iron–sulphur clusters. Analysis of the N-terminal signal sequence of DdhA suggests that it is secreted via the Tat secretory system in complex with DdhB, whereas DdhC is probably secreted via a Sec-dependent mechanism. Analysis of a ddhA mutant showed that dimethyl sulphide dehydrogenase was essential for photolithotrophic growth of Rv. sulfidophilum on dimethyl sulphide but not for chemo-trophic growth on the same substrate. Mutational analysis showed that cytochrome c2 mediated photosynthetic electron transfer from dimethyl sulphide dehydrogenase to the photochemical reaction centre, although this cytochrome was not essential for photoheterotrophic growth of the bacterium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.02978.x
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  • 2
    Digitale Medien
    Digitale Medien
    The multicopper oxidase of Pseudomonas aeruginosa is a ferroxidase with a central role in iron acquisition (2002)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 45 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Recently it has been observed that multicopper oxidases are present in a number of microbial genomes, raising the question of their function in prokaryotes. Here we describe the analysis of an mco mutant from the opportunistic pathogen Pseudomonas aeruginosa. Unlike wild-type Pseudomonas aeruginosa, the mco mutant was unable to grow aerobically on minimal media with Fe(II) as sole iron source. In contrast, both the wild-type and mutant strain were able to grow either anaerobically via denitrification with Fe(II) or aerobically with Fe(III). Analysis of iron uptake showed that the mco mutant was impaired in Fe(II) uptake but unaffected in Fe(III) uptake. Purification and analysis of the MCO protein confirmed ferroxidase activity. Taken together, these data show that the mco gene encodes a multicopper oxidase that is involved in the oxidation of Fe(II) to Fe(III) subsequent to its acquisition by the cell. In view of the widespread distribution of the mco gene in bacteria, it is suggested that an iron acquisition mechanism involving multicopper oxidases may be an important and hitherto unrecognized feature of bacterial pathogenicity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.03132.x
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  • 3
    Digitale Medien
    Digitale Medien
    Accumulation of manganese in Neisseria gonorrhoeae correlates with resistance to oxidative killing by superoxide anion and is independent of superoxide dismutase activity (2001)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 40 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: As a facultative aerobe with a high iron requirement and a highly active aerobic respiratory chain, Neisseria gonorrhoeae requires defence systems to respond to toxic oxygen species such as superoxide. It has been shown that supplementation of media with 100 µM Mn(II) considerably enhanced the resistance of this bacterium to oxidative killing by superoxide. This protection was not associated with the superoxide dismutase enzymes of N. gonorrhoeae. In contrast to previous studies, which suggested that some strains of N. gonorrhoeae might not contain a superoxide dismutase, we identified a sodB gene by genome analysis and confirmed its presence in all strains examined by Southern blotting, but found no evidence for sodA or sodC. A sodB mutant showed very similar susceptibility to superoxide killing to that of wild-type cells, indicating that the Fe-dependent SOD B did not have a major role in resistance to oxidative killing under the conditions tested. The absence of a sodA gene indicated that the Mn-dependent protection against oxidative killing was independent of Mn-dependent SOD A. As a sodB mutant also showed Mn-dependent resistance to oxidative killing, then it is concluded that this resistance is independent of superoxide dismutase enzymes. Resistance to oxidative killing was correlated with accumulation of Mn(II) by the bacterium. We hypothesize that this bacterium uses Mn(II) as a chemical quenching agent in a similar way to the already established process in Lactobacillus plantarum. A search for putative Mn(II) uptake systems identified an ABC cassette-type system (MntABC) with a periplasmic-binding protein (MntC). An mntC mutant was shown to have lowered accumulation of Mn(II) and was also highly susceptible to oxidative killing, even in the presence of added Mn(II). Taken together, these data show that N. gonorrhoeae possesses a Mn(II) uptake system that is critical for resistance to oxidative stress.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02460.x
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  • 4
    Digitale Medien
    Digitale Medien
    Xanthine dehydrogenase from the phototrophic purple bacterium Rhodobacter capsulatus is more similar to its eukaryotic counterparts than to prokaryotic molybdenum enzymes (1998)
    Oxford BSL : Blackwell Science Ltd, UK
    Molecular microbiology 27 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Fourteen Rhodobacter capsulatus mutants unable to grow with xanthine as sole nitrogen source were isolated by random Tn5 mutagenesis. Five of these Tn5 insertions were mapped within two adjacent chromosomal EcoRI fragments hybridizing to oligonucleotides synthesized according to conserved amino acid sequences of eukaryotic xanthine dehydrogenases. DNA sequence analysis of this region revealed two open reading frames, designated xdhA and xdhB, encoding xanthine dehydrogenase. The deduced amino acid sequence of XDHA contains binding sites for two [2Fe–2S] clusters and FAD, whereas XDHB is predicted to contain the molybdopterin cofactor. In contrast to R. capsulatus, these three cofactor binding sites reside within a single polypeptide chain in eukaryotic xanthine dehydrogenases. The amino acid sequence of xanthine dehydrogenase from R. capsulatus showed a higher degree of similarity to eukaryotic xanthine dehydrogenases than to the xanthine dehydrogenase-related aldehyde oxidoreductase from Desulphovibrio gigas. The expression of an xdhA–lacZ fusion was induced when hypoxanthine or xanthine was added as sole nitrogen source. Mutations in nifR1 (ntrC) and nifR4 (rpoN, encoding σ54) had no influence on xdh gene expression. A putative activator sensing the availability of substrate seems to respond to xanthine but not to hypoxanthine. The transcriptional start site of xdhA was mapped by primer extension analysis. Comparison with known promoter elements revealed no significant homology. Xanthine dehydrogenase from R. capsulatus was purified to homogeneity. The enzyme consists of two subunits with molecular masses of 85 kDa and 50 kDa respectively. N-terminal amino acid sequencing of both subunits confirmed the predicted start codons. The molecular mass of the native enzyme was determined to be 275 kDa, indicating an α2β2-subunit structure. Analysis of the molybdenum cofactor of xanthine dehydrogenase from R. capsulatus revealed that it contains the molybdopterin cofactor and not a molybdopterin dinucleotide derivative.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00733.x
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  • 5
    Digitale Medien
    Digitale Medien
    NmlR of Neisseria gonorrhoeae: a novel redox responsive transcription factor from the MerR family (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 57 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: A MerR-like regulator (NmlR –Neisseria merR-like Regulator) identified in the Neisseria gonorrhoeae genome lacks the conserved cysteines known to bind metal ions in characterized proteins of this family. Phylogenetic analysis indicates that NmlR defines a subfamily of MerR-like transcription factors with a distinctive  pattern  of  conserved  cysteines  within their primary structure. NmlR regulates itself and three other genes in N. gonorrhoeae encoding a glutathione-dependent dehydrogenase (AdhC), a CPx-type ATPase (CopA) and a thioredoxin reductase (TrxB). An nmlR mutant lacked the ability to survive oxidative stress induced by diamide and cumene hydroperoxide. It also had 〉  50-fold lower NADH-S-nitrosoglutathione oxidoreductase activity consistent with a role for AdhC in protection against nitric oxide stress. The upstream sequences of the NmlR regulated genes contained typical MerR-like operator/promoter arrangements consisting of a dyad symmetry located between the −35 and −10 elements of the target genes. The NmlR target operator/promoters were cloned into a β-galactosidase reporter system and promoter activity was repressed by the introduction of NmlR in trans. Promoter activity was activated by NmlR in the presence of diamide. Under metal depleted conditions NmlR did not repress PAdhC (or PCopA) promoter activity, but this was reversed in the presence of Zn(II), indicating repression was Zn(II)-dependent. Analysis of mutated promoters lacking the dyad symmetry revealed constitutive promoter activity which was independent of NmlR. Gel shift assays further confirmed that NmlR bound to the target promoters possessing the dyad symmetry. Site-directed mutagenesis of the four NmlR cysteine residues revealed that they were essential for activation of gene expression by NmlR.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04773.x
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  • 6
    Digitale Medien
    Digitale Medien
    Molecular analysis of the psa permease complex of Streptococcus pneumoniae (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 53 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: The psaBCA locus of Streptococcus pneumoniae encodes a putative ABC Mn2+-permease complex. Downstream of the operon is psaD, which may be co-transcribed and encodes a thiol peroxidase. Previously, there has been discordance concerning the phenotypic impact of mutations in the psa locus, resolution of which has been complicated by differences in mutant construction and the possibility of polar effects. Here, we constructed unmarked, in frame deletion mutants ΔpsaB, ΔpsaC, ΔpsaA, ΔpsaD, ΔpsaBC, ΔpsaBCA and ΔpsaBCAD in S. pneumoniae D39 to examine the role of each gene within the locus in Mn2+ uptake, susceptibility to oxidative stress, virulence, nasopharyngeal colonization and chain morphology. The requirement for Mn2+ for growth and transformation was also investigated for all mutants. Inductively coupled plasma mass spectrometry (ICP-MS) analysis provided the first direct evidence that PsaBCA is indeed a Mn2+ transporter. However, this study did not substantiate previous reports that the locus plays a role in choline-binding protein pro-duction or chain morphology. We also confirmed the importance of the Psa permease in systemic virulence and resistance to superoxide and hydrogen peroxide, as well as demonstrating a role in nasopharyngeal colonization for the first time. Further evi-dence is provided to support the requirement for Mn2+ supplementation for growth and transformation of ΔpsaB, ΔpsaC, ΔpsaA, ΔpsaBC, ΔpsaBCA and ΔpsaBCAD mutants. However, transformation, as well as growth, of the ΔpsaD mutant was not dependent upon Mn2+ supplementation. We also show that, apart from sensitivity to hydrogen peroxide, the ΔpsaD mutant exhibited essentially similar phenotypes to those of the wild type. Western blot analysis with a PsaD antiserum showed that deleting any of the genes upstream of psaD did not affect its expression. However, we found that deleting psaB resulted in decreased expression of PsaA relative to that in D39, whereas deleting both psaB and psaC resulted in at least wild-type levels of PsaA.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04164.x
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  • 7
    Digitale Medien
    Digitale Medien
    The influence of chelating agents upon the dissimilatory reduction of Fe(III) byShewanella putrefaciens. Part 2. Oxo-and hydroxo-bridged polynuclear Fe(III) complexes (1996)
    Springer
    BioMetals 9 (1996), S. 291-301 
    Details
    ISSN: 1572-8773
    Schlagwort(e): dissimilatory Fe(III) reduction ; membrane-bound Fe(III) reductase ; polynuclear Fe(III) complexes ; Shewanella putrefaciens
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The susceptibility to dissimilatory reduction of polynuclear oxo- and hydroxo-bridged Fe(III) complexes byShewanella putrefaciens intact cells and membranes has been investigated. These complexes were ligated by the potential tetradentates heidi (H3heidi =N-(2-hydroxyethyl)iminodiacetic acid) or nta (H3nta = nitrilotriacetic acid), or the potential tridentate ida (H2ida = iminodiacetic acid). A number of defined small complexes with varied nuclearity and solubility properties were employed, as well as undefined species prepared by mixing different molar ratios of ida or heidi:Fe(III) in solution. The rates of Fe(III) reduction determined by an assay for Fe(II) formation with ferrozine were validated by monitoringc-type cytochrome oxidation and re-reduction associated with electron transport. For the undefined Fe(III) polymeric species, reduction rates in whole cells and membranes were considerably faster in the presence of heidi compared to ida. This is believed to result from generally smaller and more reactive clusters forming with heidi as a consequence of the alkoxo function of this ligand being able to bridge between Fe(III) nuclei, with access to an Fe(III) reductase located at the cytoplasmic membrane being of some importance. The increases in reduction rates of the undefined ida species with Fe(III) using membranes relative to whole cells reinforce such a view. Using soluble synthetic Fe(III) clusters, slow reduction was noted for an oxo-bridged dimer coordinatively saturated with ida and featuring unligated carboxylates. This suggests that sterically hindering the cation can influence enzyme action. A heidi dimer and a heidi multimer (17 or 19 Fe(III) nuclei), which are both of poor solubility, were found to be reduced by whole cells, but dissimilation rates increased markedly using membranes. These data suggest that Fe(III) reductase activity may be located at both the outer membrane and the cytoplasmic membrane ofS. putrefaciens. Slower reduction of the heidi multimer relative to the heidi dimer reflects the presence of a central hydroxo(oxo)-bridged core containing nine Fe(III) nuclei within the former cluster. This unit is a poor substrate for dissimilation, owing to the fact that the Fe(III) is not ligated by aminocarboxylate. The faster reduction noted for the heidi dimer in membranes than for a soluble ida monomer suggests that the presence of ligating water molecules may relieve steric hindrance to enzyme attack. Furthermore, reduction of an insoluble oxo-bridged nta dimer featuring ligating water molecules in intact cells was faster than that of a soluble monomer coordinatively saturated by nta and possessing an unligated carboxylate. This suggests that steric factors may override solubility considerations with respect to the susceptibility to reduction of certain Fe(III) complexes by the bacterium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00817930
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  • 8
    Digitale Medien
    Digitale Medien
    The influence of chelating agents upon the dissimilatory reduction of Fe(III) by Shewanella putrefaciens (1995)
    Springer
    BioMetals 8 (1995), S. 163-173 
    Details
    ISSN: 1572-8773
    Schlagwort(e): cytochrome oxidation ; dissimilatory Fe(III) reduction ; Fe(III) chelators ; membrane-bound Fe(III) reductase ; Shewanella putrefaciens
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O2, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00142016
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  • 9
    Digitale Medien
    Digitale Medien
    The activities of two pathways of nitrate reduction in Rhodopseudomonas capsulata (1985)
    Springer
    Archives of microbiology 142 (1985), S. 403-408 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Nitrate assimilation ; Nitrate dissimilation ; Ammonium regulation ; Rhodopseudomonas capsulata
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract (1) The disappearance of nitrate from suspensions of intact, washed cells of Rhodopseudomonas capsulata strain N22DNAR+ was measured with an ion selective electrode. In samples taken from phototrophic cultures grown to late exponential phase, nitrate disappearance was partially inhibited by light but was not affected by the presence of ammonium. Nitrate disappearance from samples from low density cultures in the early exponential phase of growth was first inhibited and later stimulated by light. In these cells ammonium ions inhibited the light-dependent but not the dark disappearance of nitrate. It is concluded that cells in the early exponential phase of growth possess both an ammonium-sensitive, assimilatory pathway for nitrate reduction (NRI) and an ammonium-insensitive pathway for nitrate reduction (NRII) which is linked to respiratory electron flow and energy conservation. In cells harvested in late exponential phase only the respiratory pathway for pitrate reduction is detectable. (2) Nitrate reduction, as judged by the oxidation of reduced methyl viologen by anaerobic cell suspensions, was measured at high rates in those strains of R. capsulata (AD2, BK5, N22DNAR+) which are believed to possess NRII activity but not in those strains (Kbl, R3, N22) which only manifest the ammonium-sensitive NRI pathway. On this basis we have used nitrate-dependent oxidation of reduced methyl viologen as a diagnostic test for the nitrate reductase of NRII in cells harvested from cultures of R. capsulata strain AD2. The activity was readily detectable in cells from cultures grown aerobically in the dark with ammonium nitrate as source of nitrogen. When the oxygen supply to the culture was withdrawn, the level of methyl viologen-dependent nitrate reductase increased considerably and nitrite accumulated in the culture medium. Upon reconnecting the oxygen supply, methyl viologen-dependent nitrate reductase activity decreased and the reduction of nitrate to nitrite in the culture was inhibited. It is concluded that the respiratory nitrate reductase activity is regulated by the availability of electron transport pathways that are linked to the generation of a proton electrochemical gradient.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00491912
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  • 10
    Digitale Medien
    Digitale Medien
    Identification of a periplasmic dimethylsulphoxide reductase in Hyphomicrobium EG grown under chemolithoheterotrophic conditions with dimethylsulphoxide as carbon source (1994)
    Springer
    Archives of microbiology 162 (1994), S. 148-150 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Hyphomicrobium ; Dimethylsulphoxide reductase ; Periplasmic enzymes ; Chemolithoheterotrophic growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Hyphomicrobium EG can grow with dimethylsulphoxide as sole carbon and energy source with oxygen as electron acceptor. In the present work we have found that the dimethylsulphoxide reductase of this bacterium could be assayed with dithionite-reduced methylviologen as reductant but not with NADH. Sub-cellular fractionation of Hyphomicrobium EG showed that the dimethylsulphoxide reductase was a periplasmic enzyme. An antibody to the dimethylsulphoxide reductase of Rhodobacter capsulatus cross-reacted with a polypeptide in the periplasmic fraction from Hyphomicrobium EG which had the same M r as the dimethylsulphoxide reductase of Rhodobacter capsulatus. It is suggested that the reduction of dimethylsulphoxide in Hyphomicrobium involves respiratory electron transfer.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00264389
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