Investigating the Interaction of PqsE and RhlR in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen, responsible for causing multi-drug resistant infections in immunocompromised patients. P. aeruginosa pathogenicity is largely controlled through quorum sensing (QS), the process of bacterial cell-cell communication mediated by the release and detection of small molecule signals, called autoinducers. One major branch of QS in P. aeruginosa, the rhl branch, controls the release of several virulence factors. Interestingly, a protein, PqsE, that is annotated to be part of a separate QS system, has been implicated in activation of the rhl system. Preliminary work in the Bassler group has shown that PqsE makes a direct protein-protein interaction with the QS receptor of the rhl system, RhlR, in vitro. This study attempts to prove the hypothesis that PqsE and RhlR engage in a protein-protein interaction and that they regulate similar genes, potentially as a result of this interaction. Isolation and sequencing of RNA from ∆pqsE and rhl pathway mutant P. aeruginosa strains revealed a number of genes regulated by PqsE, RhlR, and RhlI, the rhl system auto-inducer synthase. Importantly, many genes were regulated by both PqsE and RhlR as predicted, suggesting a link between PqsE and the rhl system. Further, immunoprecipitation and mass spectrometry provided evidence that PqsE engages in a direct protein-protein interaction with RhlR. Data from the immunoprecipitation experiments also showed that PqsE is potentially involved in a number of other systems in P. aeruginosa such as the production of autoinducers, the regulation of drug efflux pumps and membrane porins, and the production of acetyl-CoA. Together, the results presented herein provide evidence of the PqsE-RhlR interaction and suggest that it may be a major driver of virulence and a much-needed potential drug target for treating P. aeruginosa infections.