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  • 1
    Electronic Resource
    Electronic Resource
    The rpfA gene of Xanthomonas campestris pathovar campestris, which is involved in the regulation of pathogenicity factor production, encodes an aconitase (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 28 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Xanthomonas campestris pv campestris (Xcc) is a plant pathogenic bacterium that controls the production of pathogenicity factors in part by a cluster of genes designated rpf (regulation of pathogenicity factors). Sequence analysis of one of these genes (rpfA) revealed an open reading frame with amino acid sequence similarity to aconitases from other bacteria. Aconitase activity was lower in cellular extracts of an rpfA::Tn5 mutant than in those from the wild type. A zymogram of aconitase activity after native gel electrophoresis showed the presence of two distinct aconitases in Xcc; the major aconitase was absent in the rpfA::Tn5 mutant. This mutant also had reduced levels of extracellular enzymes and extracellular polysaccharide (EPS). Supplying rpfA in trans to the rpfA::Tn5 mutant restored both the major aconitase activity and the synthesis of these pathogenicity factors. The transcription of the genes for two extracellular enzymes (prtA, encoding a serine protease, and engXCA, encoding endoglucanase) was reduced in the rpfA mutant background. Because some eukaryotic aconitases are also involved in iron regulation, we explored a possible connection between rpfA and iron metabolism. Intracellular iron levels in the mutants were lower than in the wild type as assessed by sensitivity to the iron-activated antibiotic, streptonigrin. Wild-type bacteria grown in iron-deficient conditions had a similar sensitivity to streptonigrin as the aconitase mutant. Overall, these results suggest that a prokaryotic aconitase can also act as a regulator of gene expression and that the regulation is possibly related to changes in intracellular iron levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.00852.x
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  • 2
    Electronic Resource
    Electronic Resource
    A novel regulatory system required for pathogenicity of Xanthomonas campestris is mediated by a small diffusible signal molecule (1997)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 24 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Mutations in the seven clustered rpf genes cause downregulated synthesis of extracellular enzymes and reduced virulence of Xanthomonas campestris pathovar campestris (Xcc). The phenotype of mutants in one of the genes, rpfF, can be restored by a diffusible extracellular factor (DSF) produced by all Xcc strains tested, apart from rpfF and rpfB mutants. DSF accumulates in early stationary phase (when synthesis of enzymes is maximal), but levels decline subsequently. Addition of DSF to exponentially-growing wild-type bacteria does not cause precocious enzyme synthesis. rpfB and rpfF are expressed throughout growth, but the rate increases in early stationary phase. RpfB is predicted to be a long-chain fatty acyl CoA ligase, and RpfF shows some relatedness to enoyl CoA hydratases. The properties of DSF suggest that it may be a fatty-acid derivative, and certain lipid preparations possess DSF activity at higher concentrations. These include lipid extracts and acid-hydrolysed lipopolysaccharide and lipid A from Xcc, and purified dodecanoic and hydroxydodecanoic acid. DSF production is confined to certain xanthomonads. We propose a model for the DSF system, which represents a novel mechanism for regulating virulence factor synthesis in response to physiological or environmental changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.3721736.x
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  • 3
    Electronic Resource
    Electronic Resource
    A mutation that blocks exopolysaccharide synthesis prevents nodulation of peas by Rhizobium leguminosarum but not of beans by R. phaseoli and is corrected by cloned DNA from Rhizobium or the phytopathogen Xanthomonas (1986)
    Springer
    Molecular genetics and genomics 203 (1986), S. 320-323 
    Details
    ISSN: 1617-4623
    Keywords: Exopolysaccharide ; Legume ; Nodules ; Rhizobium ; Xanthomonas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A Tn5-induced mutant strain of R. phaseoli which failed to synthesize exopolysaccharide (EPS) was isolated and was shown to induce normal nitrogen-fixing nodules on Phaseolus beans, the host of this Rhizobium species. The corresponding wild-type Rhizobium DNA was cloned in a wide host-range vector and by isolating Tn5 insertions in this cloned DNA, mutations in a gene termed pss (polysaccharide synthesis) were isolated. These were introduced by marker exchange into near-isogenic strains of R. leguminosarum and R. phaseoli which differed only in the identity of their symbiotic plasmids. Whereas the EPS-deficient mutant strain of R. phaseoli induced normal nitrogen-fixing nodules on Phaseolus beans, the same mutation prevented nodulation of peas by a strain of R. leguminosarum which normally nodulates this host. Further, it was found that DNA cloned from the plant pathogen Xanthomonas campestris pathover campestris could correct the defect in EPS synthesis in R. leguminosarum and R. phaseoli and also restored the ability to nodulate peas to the pss::Tn5 mutant strain of R. leguminosarum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333974
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic and molecular analysis of a cluster of rpf genes involved in positive regulation of synthesis of extracellular enzymes and polysaccharide in Xanthomonas campestris pathovar campestris (1991)
    Springer
    Molecular genetics and genomics 226 (1991), S. 409-417 
    Details
    ISSN: 1617-4623
    Keywords: Two-component regulatory system ; Pathogenicity ; Xanthan ; DNA sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cosmid clone. pIJ3020 containing DNA from the plant pathogenic bacterium Xanthomonas campestris pathovar campestris has previously been shown to complement a non-pathogenic mutant defective in synthesis of extracellular enzymes. The DNA cloned in pIJ3020 was analysed by mutagenesis with Tn5 and Tn5lac and by nucleotide sequencing. The results indicate that this region of the genome contains a cluster of genes, mutation in any of which results in failure of the enzymes and extracellular polysaccharide to be synthesized. The designation rpf (regulation of pathogenicity factors) is proposed for these genes. The nucleotide sequence of one gene (rpfC) predicts a protein product with homology to conserved domains of both sensor and regulator proteins of prokaryotic two-component regulatory systems, which are usually involved in regulating gene expression in response to environmental stimuli.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00260653
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular cloning of protease gene(s) from Xanthomanas campestris pv. campestris: Expression in Escherichia coli and role in pathogenicity (1987)
    Springer
    Molecular genetics and genomics 210 (1987), S. 443-448 
    Details
    ISSN: 1617-4623
    Keywords: Cloning ; Xanthomonas ; Protease ; Pathogenicity ; Brassica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The recombinant plasmid pIJ3070 isolated from a genomic library of Xanthomonas campestris pv. campestris constructed in the conjugal cosmid pLAFR3 contains protease gene(s) which can be expressed in Escherichia coli. Tn5 mutagenesis and subcloning revealed that the protease structural gene(s) is(are) located in a ca. 10 kb EcoRI fragment. Several protease-minus mutants of X. c. campestris were obtained by Tn5 mutagenesis of pIJ3070 and marker exchange techniques. Studies of pathogenicity of these Tn5 mutants showed that the protease is not critically important for the pathogenicity of X. c. campestris on turnip plants but may play a minor role in disease development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327195
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