Calcium regulating quorum sensing in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is known to cause numerous severe human infections, including those that become lethal in cystic fibrosis (CF) patients. Since CF patients have abnormally high levels of calcium in their fluids, this project focuses on the effects of varying calcium conditions on the expression of virulence factors produced by P. aeruginosa. The quorum-sensing (QS) molecules found in the bacterium are responsible for cell-to-cell communication that controls the expression of numerous genes including those encoding virulence factors. LasI, RhlI, and PqsA are the three main synthases in the QS system. A promoter activity assay was used to monitor the expression of the lasI, rhlI, and pqsA promoter regions by measuring the luminescence they produced at 0- and 5-mM calcium conditions, over a 14-hour time period. Results illustrated that calcium upregulated the expression of these promoter regions. To determine which component of the calcium signaling system in P. aeruginosa is responsible for this activation, deletion mutants lacking either the calcium channel (CalC), calcium sensor (EfhP), or calcium regulator (CarR) were constructed. The luminescence produced by the promoter regions in the wild type (PAO1) as well as the CalC deletion mutant were monitored, and results showed CalC to be involved in the calcium regulation of the QS genes.