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Identification and Characterization of Virulence Factors in the Principal Pathogenic Species of the Burkholderia cepacia complex Open Access


Other title
non-ribosomal peptide synthetase
low oxygen
Lemna minor
Burkholderia cepacia
virulence factors
type VI secretion
Type of item
Degree grantor
University of Alberta
Author or creator
Thomson, Euan Lewis Sproull
Supervisor and department
Jonathan Dennis, Biological Sciences
Examining committee member and department
Stefan Pukatzki, Department of Medical Microbiology and Immunology, University of Alberta
Susan Jensen, Department of Biological Sciences, University of Alberta
Randy Irvin, Department of Medical Microbiology and Immunology, University of Alberta
Doug Storey, Department of Biological Sciences, University of Calgary
Department of Biological Sciences
Microbiology and Biotechnology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Cystic fibrosis (CF) is the most common heritable disease among Caucasian populations, with afflicted individuals experiencing a immune, respiratory and digestive system complications. Compromised mucus clearance from the CF airway provides a habitat for bacteria and generates oxygen gradients within the mucus. Members of the Burkholderia cepacia complex (Bcc) are devastating airway pathogens of CF patients, with innate antibiotic resistance and the propensity to establish invasive necrotic infections. Their mechanisms of infection remain largely uncharacterized, though a number of virulence factors have been identified using standard model hosts. Among these factors are gene products common in human pathogens, interlaced by a complex regulatory network comprising global regulators, communication networks and environmental sensors. The objective of this study is to identify and detail virulence elements of the most prevalent Bcc species in the CF community using established model systems and a novel high-throughput plant host, Lemna minor (Common duckweed). First, a strong correlation was found between the relative virulence of Bcc strains in duckweed and the established insect model, Galleria mellonella (Greater wax moth larva). A non-ribosomal peptide synthestase gene cluster was identified in B. vietnamiensis and shown to cause erythocyte lysis and contribute to virulence in the larval model. To identify virulence factors in B. cenocepacia, 5,980 plasposon mutants were screened for attenuation against duckweed. Several novel virulence factors were found, including a regulator, a putative DNA binding protein, and metabolism-related proteins. Type VI secretion was studied for its contribution to B. cenocepacia virulence, but showed only antibacterial activity against Escherichia coli, suggesting a role for Bcc type VI secretion in competitive colonization of the CF lung. Finally, the engimatic B. multivorans, which demonstrates negligible virulence effects in most model hosts but accounts for nearly half of Bcc infections in CF, demonstrated virulence activation in both low oxygen and high temperature, indicating a regulatory effect of these CF-relevant environmental cues akin to the recently-identified lxa locus in B. cenocepacia. This finding indicates that standard infection models may be insufficient for characterizing this pathogen, and approaches that allow modified environmental conditions may be required to fully understand Bcc pathogenesis.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Thomson, E.L.S. and Dennis, J.J. 2012. A Burkholderia cepacia complex non-ribosomal peptide-synthesized toxin is hemolytic and required for full virulence. Virulence 3(3):288-98.

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