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Burkholderia cepacia is a gram-negative bacterium that is a known pathogen of plants and humans. B. cepacia was first described as the causative agent of sour skin rot in onion crops and has more recently been recognized as an opportunistic pathogen in cystic fibrosis patients where it is able to colonize the airway and cause rapid pulmonary decline. There are limited treatments available for this bacterium due to its innate resistance to antibiotics, and the mechanisms of virulence used by B. cepacia in different contexts are not well understood. This work aims to identify and describe virulence factors necessary for B. cepacia pathogenesis. Transposon mutagenesis in B. cepacia ATCC 25416, followed by a virulence assay that screened mutants using an onion infection model, was used to identify mutants of interest. A variety of phenotypes were observed, and mutant 169 was selected for follow-up studies as it generated smaller wounds as soon as 24 hours post-infection. Genetic characterizations determined that the transposon inserted in the rfbB gene which is the first gene in a five gene operon within chromosome 1. Analysis of cDNA generated from the operon concluded that the rfbB and downstream genes are not expressed in the mutant. Therefore, the inactivation of the entire operon is responsible for the observed phenotype. This gene likely encodes a virulence factor, as the disruption does not alter bacterial growth in rich media or the formation of biofilms. rfbB shows homology to genes encoding glucose dehydratase, which plays a role in the synthesis of the O-antigen of lipopolysaccharide (LPS). The disturbance in this outer membrane component may point towards the pathogen’s inability to interact with host cells. Therefore, current work is focused on characterizing structural differences in the LPS molecules produced by the rfbB mutant and the wildtype strain and assessing the binding and invasion efficiency of these two strains in a plant model of infection. In doing so, this potential virulence factor can be characterized and then applied to further the understanding of the infection process.


Dr. Elizabeth Danka, Biology

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biology, gene expression, bacterium

Characterization of rfbB as a virulence-associated gene in B. cepacia

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