Characterizing the Novel GIG Operon in Legionella pneumophila

Legionella pneumophila, the number one cause of waterborne outbreaks in the US, 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 neither metal is well described in Legionella. We identified an operon, lpg2105-2108, demonstrating homology 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. Bioinformatic tools were used to assess the prevalence of the operon in sequenced bacteria and to known as well as uncharacterized Legionella species. A basal level expression was evident in all cultures, but a significant increase in expression was observed in response to gold and copper addition. Bioinformatic analysis revealed the presence of homologs to the GIG operon in 100+ different species of bacteria. We hypothesize that the Legionella pneumophila gold induced genes(GIG) could play a role in bacterial persistence in man-made aquatic systems. Understanding the mechanism of bacterial response to gold/copper could lead to new targets for disinfection and prevention of Legionella in water systems