Jorth, P. A. | Search bioRxiv

bioRxiv2026

Proteolytic feedback of quorum sensing promotes infection by Pseudomonas aeruginosa

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.

microbiology↗

bioRxiv2020

Inhibition of AlgU by MucA is required for viability in Pseudomonas aeruginosa

During decades-long infections in the cystic fibrosis (CF) airway, Pseudomonas aeruginosa undergoes selection. One bacterial genetic adaptation often observed in CF isolates is mucA mutations. MucA inhibits the sigma factor AlgU. Mutations in mucA lead to AlgU misregulation, resulting in a mucoid phenotype that is associated with poor CF disease outcomes. Due to its ability to be mutated, mucA is assumed to be dispensable for bacterial viability. Here we show that, paradoxically, a portion of mucA is essential in P. aeruginosa. We demonstrate that mucA is no longer required in a strain lacking algU, that mucA alleles encoding for proteins that do not bind to AlgU are insufficient for viability, and that mucA is no longer essential in mutant strains containing AlgU variants with reduced sigma factor activity. Furthermore, we found that overexpression of algU prevents cell growth in the absence of MucA, and that this phenotype can be rescued by overproduction of RpoD, the housekeeping sigma factor. Together, these results suggest that in the absence of MucA, the inability to regulate AlgU activity results in the loss of bacterial viability. Finally, we speculate that essentiality of anti-sigma factors that regulate envelope function may be a widespread phenomenon in bacteria.

microbiology↗