Small Molecule Disruption of Quorum Sensing Cross-Regulation in Pseudomonas aeruginosa Causes Major and Unexpected Alterations to Virulence Phenotypes

Abstract

The opportunistic pathogen Pseudomonas aeruginosa uses three interwoven quorum-sensing (QS) circuits—Las, Rhl, and Pqs—to regulate the global expression of myriad virulence-associated genes. Interception of these signaling networks with small molecules represents an emerging strategy for the development of anti-infective agents against this bacterium. In the current study, we applied a chemical approach to investigate how the Las-Rhl-Pqs QS hierarchy coordinates key virulence phenotypes in wild-type P. aeruginosa. We screened a focused library of synthetic, non-native N-acyl l-homoserine lactones and identified compounds that can drastically alter production of two important virulence factors: pyocyanin and rhamnolipid. We demonstrate that these molecules act by targeting RhlR in P. aeruginosa, a QS receptor that has seen far less scrutiny to date relative to other circuitry. Unexpectedly, modulation of RhlR activity by a single compound induces inverse regulation of pyocyanin and rhamnolipid, a result that was not predicted using genetic approaches to interrogate QS in P. aeruginosa. Further, we show that certain RhlR agonists strongly repress Pqs signaling, revealing disruption of Rhl-Pqs cross-regulation as a novel mechanism for QS inhibition. These compounds significantly expand the known repertoire of chemical probes available to study RhlR in P. aeruginosa. Moreover, our results suggest that designing chemical agents to disrupt Rhl-Pqs crosstalk could be an effective antivirulence strategy to fight this common pathogen.

Investment in secreted enzymes during nutrient-limited growth is utility dependent

“…Our analysis of the growth of P. aeruginosa on casein opens up the possibility of quantitative study of other secreted products with respect to the environment to better understand and predict the rate of growth of bacteria in more complex and diverse environments containing different types of polymeric substrates. Understanding which autoinducers or combinations of autoinducers relay information about the benefits and costs of different potential secreted products will be an important step in the development of quorum-sensing inhibitors targeted against specific secretion profiles associated with virulence in different environmental niches (49,50).…”

Potent and Selective Modulation of the RhlR Quorum Sensing Receptor by Using Non‐native Ligands: An Emerging Target for Virulence Control in Pseudomonas aeruginosa

“…[22] We recently reported a small set of synthetic RhlR ligands that strongly modulate virulence phenotypes in P. aeruginosa . [23] These compounds were all AHL-derived and capable of either strong RhlR agonism or antagonism. In the current study, we sought to follow up on this past work and (i) further explore the chemical space for RhlR agonism and antagonism by non-native AHLs, (ii) determine their relative efficacies and potencies, and (iii) examine the selectivities of lead compounds for RhlR over LasR and QscR.…”

Design, synthesis and biological evaluation of 4-(alkyloxy)-6-methyl-2H-pyran-2-one derivatives as quorum sensing inhibitors

“…[13][14][15] A number of QS-modulating ligands have been designed and synthesized by mimicking the natural auto-inducers such as OdDHL, BHL or PQS. [16][17][18][19][20][21][22][23][24][25][26][27] According to structure-activity relationship (SAR) studies of the synthesized QS ligands, the hydrophilic group (e.g., lactone, quinolone) and the lipophilic alkyl chains are essential for the QS-modulating activity. [28][29][30][31][32][33] Inhibitors that block the complex formation between auto-inducers and the cognate receptors could downregulate the transcription of QS-associated genes and diminish or halt the virulence of P. aeruginosa.…”