Proteolytic feedback of quorum sensing promotes infection by Pseudomonas aeruginosa

Abstract

Quorum sensing (QS) enables bacteria to coordinate collective behaviors in response to population density. However, the mechanisms by which QS circuits are reset or attenuated remain poorly understood. In Pseudomonas aeruginosa, the LuxR-type transcription factor RhlR controls virulence gene expression at high cell density, requiring both its cognate acyl-homoserine lactone signal and the accessory protein PqsE for full activity. Here, we show that RhlR abundance is actively controlled by ATP-dependent proteolysis through a self-limiting negative feedback loop. We identify an N-terminal degron within RhlR that is protected from protease recognition by PqsE binding and is required for degradation by both the Lon and the ClpP1-ClpP2 protease complex. Removal of this degron stabilizes RhlR, advancing the timing of QS-regulated gene expression, enhancing biofilm formation, imposes a competitive fitness cost in vitro, and reduced virulence in an acute mouse lung infection. Mechanistically, RhlR directly activates transcription of clpP2, encoding a subunit of the protease complex required for its own degradation, establishing a self-limiting negative feedback loop. Disruption of RhlR DNA binding stabilizes the receptor through dual effects on reduced clpP2 expression and increased PqsE availability via the loss of RhlR-dependent repression of pqsE. Together, these findings reveal proteolytic turnover as an underappreciated regulatory layer of QS-activation and establish a mechanism for how receptor turnover may facilitate the transition away from high-cell density states.