Biology subjects

Mallery, C. P.

Publications and source records attributed to Mallery, C. P..

3 recordsLinked to original sources

bioRxiv2026

The conserved coordination of acyl-homoserine lactone and PqsE signaling defines the RhlR-dependent quorum-sensing network in Pseudomonas aeruginosa clinical isolates

Quorum sensing (QS) enables Pseudomonas aeruginosa to coordinate virulence and biofilm formation through cell density-dependent signaling. In clinical isolates from patients with cystic fibrosis (pwCF), mutations in canonical QS systems such as lasR and rhlI often lead to altered signaling hierarchies that complicate our understanding of QS regulation during chronic infection. Here, we dissect the relative contributions of the autoinducer N-butyryl-L-homoserine lactone (C4HSL) and the protein binding partner PqsE to RhlR-dependent transcription in CF clinical isolates. Using site-directed mutagenesis to generate RhlR and PqsE variants incapable of responding to C4HSL (RhlR A44M) or dimerizing to interact with RhlR (PqsENI), we show that both inputs are essential for the full expression of QS-regulated virulence factors, including pyocyanin and rhamnolipids. Transcriptomic analyses revealed that C4HSL and PqsE co-regulate a conserved set of 28 RhlR-dependent genes, encompassing canonical virulence loci as well as uncharacterized genes that are likely important for adaptation to the CF airway environment. These findings establish that clinical isolates maintain functional QS circuitry reliant on dual activation of RhlR by both C4HSL and PqsE, revealing a conserved regulatory module that underpins pathogenic behavior across genetically diverse isolates. AUTHOR SUMMARYUnderstanding quorum-sensing regulation in clinical isolates of Pseudomonas aeruginosa is essential to determine how the pathogen persists and adapts within the cystic fibrosis lung. While most studies have focused on laboratory strains, chronic isolates exhibit distinct genetic and regulatory adaptations that complicate our ability to generalize quorum sensing function. Our work defines the coordinated roles of C4HSL and PqsE in activating RhlR-dependent gene expression and virulence factor production in isolates from patients with cystic fibrosis. We identify a conserved core of quorum-sensing-regulated genes that remain dependent on both signals despite extensive genomic divergence. These findings highlight that, even within the evolutionary landscape of chronic infection, quorum-sensing signaling through RhlR remains a central and conserved determinant of virulence. By resolving the dual contributions of acyl-homoserine lactone and PqsE-mediated activation, this work provides a mechanistic foundation for future efforts to therapeutically target quorum-sensing pathways in clinical P. aeruginosa infections.

microbiology↗

bioRxiv2025

RhlR quorum-sensing receptor ligand sensitivity regulates the differential expression of phenazine genes in Pseudomonas aeruginosa

Bacteria control individualistic and group behaviors using a form of cell-cell communication called quorum sensing. Quorum sensing relies on the production of chemical signals called autoinducers and the subsequent detection of those signals by a cognate receptor. Many Gram-negative bacteria use the LuxR-type family of transcription factor receptors that bind to acyl-homoserine lactone autoinducer signals to regulate their function as DNA-binding proteins. A subclass of this family of transcription factor receptors requires their cognate autoinducer to fold and dimerize to bind DNA to regulate gene expression and, thus, traits associated with quorum sensing, such as biofilm formation and virulence factor production. Here, we use a chemical-genetic approach to determine the structural basis for ligand selection by the quorum-sensing receptor RhlR from Pseudomonas aeruginosa. The native ligand for RhlR is N-butyryl-L-homoserine lactone, and this protein-ligand interaction is important for initiating gene expression in P. aeruginosa. We determine key residues that drive ligand specificity and selectivity of RhlR to define the role of ligand-driven RhlR-dependent gene regulation of quorum-sensing traits, namely the differential expression of the phenazine genes, which encode the enzymes responsible for the synthesis of the redox-sensitive virulence factor pyocyanin, among other phenazines. Furthermore, we provide a chemical-genetic framework for future studies aimed at disrupting the RhlR-ligand interaction to suppress virulence in P. aeruginosa, an important nosocomial pathogen with widespread antimicrobial resistance.

microbiology↗

bioRxiv2024

Evolution of PqsE as a Pseudomonas aeruginosa-specific regulator of LuxR-type receptors: insights from Pseudomonas and Burkholderia

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that poses a significant public health threat, particularly in healthcare settings. A key determinant of P. aeruginosa virulence is the regulated synthesis and release of extracellular products, which is controlled by a cell density-dependent signaling system known as quorum sensing (QS). P. aeruginosa uses a complex QS network, including two systems that rely on diffusible N-acylhomoserine lactone (AHL) signal molecules. The LuxR-type receptor RhlR is unique in that it requires not only its cognate AHL but also the accessory protein PqsE to maximally bind to promoter DNA and to initiate transcription. Our group demonstrated that PqsE physically interacts with RhlR, enhancing its affinity for target promoters across the P. aeruginosa genome. Although LuxR-type receptors are widespread in Gram-negative bacteria and important for pathogenesis, PqsE orthologs are restricted to Pseudomonas and Burkholderia species. This study explored the conservation of PqsE and examined PqsE ortholog structure-function across different species. Our results show that PqsE in Pseudomonas retain their functional interactions with RhlR homologs, unlike PqsE orthologs in Burkholderia spp., which do not interact with their respective LuxR-type receptors. Additionally, we assessed the AHL preferences of different receptors and hypothesized that the PqsE-RhlR interaction evolved to stabilize the inherently unstable RhlR, preventing its degradation. Indeed, we observe higher levels of RhlR protein turnover in a strain lacking pqsE compared to WT, which can be rescued in a strain lacking the Lon protease. IMPORTANCEPseudomonas aeruginosa, a major pathogen for patients with cystic fibrosis and a primary constituent of healthcare-associated infections, relies on a complex quorum-sensing (QS) network to coordinate virulence factor production. Central to this system is the interaction between two proteins, PqsE and RhlR, which drive gene expression essential for pathogenesis. Our study investigates the conservation of the PqsE-RhlR interaction across related bacterial species, revealing that PqsE in Pseudomonas can enhance RhlR activity, while orthologs in Burkholderia lack this capacity. These findings offer new insights into the specificity and evolution of QS mechanisms, highlighting the PqsE-RhlR interaction as a potentially selective target for treating P. aeruginosa infections.

microbiology↗