Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Microbiology and Immunology


Dr. Miguel A. Valvano

Second Advisor

Dr. David Heinrichs

Third Advisor

Dr. Charlie Trick


Burkholderia cenocepacia is an opportunistic pathogen that causes serious lung infections in cystic fibrosis patients. Very little is known about the mechanisms by which this organism causes disease and persists in the lungs. Our laboratory has identified mgtC as a gene necessary for the survival of Burkholderia cenocepacia in vivo (Hunt et al, 2004). We therefore investigated the role of this gene in the pathogenesis of B. cenocepacia. Genetic analyses employing mutagenesis and complementation studies revealed that MgtCBCAM1867 was required for growth of B. cenocepacia in magnesium- depleted medium and for bacterial survival within murine macrophages. The role of MgtC in intracellular survival may not be related to low Mg2+ but rather to other macrophage-killing mechanisms. We compared the growth in vitro of wild type and mgtC-deficient B. cenocepacia in the presence of compounds thought to mimic in vivo conditions. In addition, experiments using a macrophage infection model were performed using inhibitors of specific macrophage responses. We have demonstrated that the reduced intracellular survival of the mgtC mutant in macrophages is not due to increased sensitivity to low pH, oxidative stress, nitrosative stress, potassium concentration, oxygen tension or cationic peptides, nor does it appear to be the consequence of a general membrane defect since mgtC mutants can resist detergents and antimicrobial peptides. To elucidate how MgtC may be involved in protecting B. cenocepacia from the intracellular environment of the host cells we investigated the regulation of mgtC and characterized the MgtC protein. We have demonstrated that in vitro, mgtC is constitutively expressed and encodes an integral membrane protein that is heat- labile. Mutagenesis studies revealed that the C-terminus of the protein is cytosolic and is critical for protein function, both in vitro and in vivo. In addition, cross-linking experiments show that MgtC multimerizes and may interact with another protein independently of the C-terminal tail. Characterization of the role of mgtC in the pathogenesis of B. cenocepacia and other organisms with an intracellular phase has only just begun but our data emphasize its importance for infection. Further investigation of the physiological role and mechanism of MgtC will help shed light on how B. cenocepacia is able to persist in the lungs and survive intracellularly.



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