Quinolone and acyl-homoserine lactone quorum sensing in chronic P. aeruginosa infections

Project Summary Quorum sensing (QS) is a cell-cell communication system used by many bacteria to regulate gene expression in a coordinated manner. Our work focuses on the QS system of Pseudomonas aeruginosa, a saprophyte and opportunistic pathogen of humans. P. aeruginosa uses QS to regulate dozens of genes, including several important virulence factors. P. aeruginosa QS is mediated by the transcription factors LasR and RhlR, which respond to acyl-homoserine lactone signals, and PqsR, which responds to alkylquniolone signals. Initial characterizations of QS in P. aeruginosa described a hierarchy: LasR regulates RhlR and PqsR activity. Over the past several years we, and others, have shown that this hierarchy is malleable. RhlR and PqsR can be active in the absence of functional LasR in isolates from many settings, particularly those isolated from the chronic lung infections of people with cystic fibrosis (CF). These results suggest a “rewiring” of QS that is critical to the maintenance of virulence functions in chronic infections. This proposal builds on our previous observations to ask about the biological significance of this alternate hierarchy in bacterial isolates from people with CF. We make use of CF isolates and a laboratory model strain to ask i) how is the architecture of QS of P. aeruginosa altered?; ii) in this altered hierarchy, how do RhlR and PqsR QS interact to effect virulence functions in isolates from chronic infection?; and iii) what is the role of a highly-conserved, uniformly QS regulated, non-ribosomal peptide synthetase? The answers to these questions will define the central importance of RhlR and PqsR in P. aeruginosa from chronic infections and inform future efforts to design therapeutics targeting RhlR or PQS QS in this bacterium.