Date of Award

5-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Microbiology

Advisor

McNealy, Tamara

Committee Member

Wells, Christina

Committee Member

Bruce, Terri

Abstract

Legionella pneumophila is the number one cause of waterborne outbreaks in the US. It contaminates man-made water systems increasing exposure risk for Legionnaire’s Disease. Copper/silver ionization is one common method for managing L. pneumophila in water systems, but bacterial response mechanisms to these metals are not well described in Legionella. We identified an operon, lpg2105-2108, that is homologous to known gold/copper response genes in Cupriavidus metallidurans. Using a GFP reporter gene system, we measured transcriptional activity of the lpg2105-2108 operon in L. pneumophila strain Lp02 in response to 20µM or 50µM of HAuCl4 or CuSO4 in planktonic and biofilm cultures. We then used bioinformatic tools to assess the prevalence of the operon in known as well as uncharacterized Legionella species. A constant basal level expression was evident in all cultures, but a significant increase in expression was observed in response to gold and copper addition during stationary phase. Analysis of the LetA transcriptional regulatory mutant showed no difference in activity compared to the wild type. Reporter gene analysis of the operon in E. coli DH5α, which lacks the operon in its genome, showed basal level expression, but no response to gold or copper. We hypothesize that the Legionella pneumophila gold induced genes (GIG) operon could play a role in bacterial persistence in man-made aquatic systems. Understanding the mechanism of bacterial response to gold and copper could lead to new targets for disinfection and prevention of Legionella in water systems.

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