http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Analysis of virulence and pathogenic determinants in Burkholderia cepacia
Burkholderia cepacia strain K56-2, a genomovar III representative of the B. cepacia complex, is part of the epidemic and clinically problematic ET12 lineage. The strain produced plant tissue watersoaking (ptw) on onion tissue, which is a plant disease associated trait. Using plasposon mutagenesis, mutants in the ptw phenotype were generated. The translated sequence of a disrupted (ptwD) gene from a ptw-negative mutant showed homology to TraD of the F-plasmid transfer cluster. Analysis of the region proximal to the transfer gene homologue resulted in the identification of a cluster of 11 genes (ptwD, I, E, B, C, W, U, N F, H and G) on a 40 kb locus with translated products that showed homology to proteins associated with known type IV secretion systems. The roles of ptwD, I and C in ptw activity and plasmid transfer were analyzed by conducting site-directed mutagenesis followed by using allelic exchange. The ptw phenotype was not observed in K56-2 derivatives with a disruption in ptwD or ptwC, but was observed in a derivative with a disruption in ptwI. Plasmid pMMB207αβ was mobilized by B. cepacia into an isogenic strain and Pseudomonas syringae at frequencies of 10⁻² and 10⁻⁴ transconjugants per recipient, respectively. Plasmid mobilization was not detected when derivative strains with mutations in ptwD, I or C were used as donors. In addition, analysis of cultural supernatants revealed that the putative ptw effector(s) was a secreted, heat-stable protein(s) that caused plasmolysis of plant protoplasts. This is the first report of a type IV secretion system in B. cepacia that mediates both transfer of DNA and secretion of a cytotoxic protein(s). The experiments described in this dissertation provide a foundation for further analysis of the B. cepacia complex and the role of the type IV secretion system in disease of both plants and humans.
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Includes bibliographical references (leaves 76-82).