Molecular Mechanisms of Phosphate Stress Activation of Pseudomonas aeruginosa Quorum Sensing Systems.

Xianfa Meng,Stephen Dela Ahator,Lian-Hui Zhang,Craig D Ellermeier

doi:10.1128/msphere.00119-20

Xianfa Meng, Stephen Dela Ahator + Show 2 more

Open Access

https://doi.org/10.1128/msphere.00119-20

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Journal: mSphere	Publication Date: Mar 18, 2020
Citations: 42	License type: CC BY 4.0

Affiliation: South China Agricultural University

Abstract

The hierarchical quorum sensing (QS) systems of Pseudomonas aeruginosa, consisting of las, pqs, and rhl, coordinate the expression of bacterial virulence genes. Previous studies showed that under phosphate deficiency conditions, two-component regulatory system PhoRB could activate various genes involved in cytotoxicity through modulation of QS systems, but the mechanism by which PhoR/PhoB influences QS remains largely unknown. Here, we provide evidence that among the key QS regulatory genes in P. aeruginosa, rhlR, pqsA, mvfR, and lasI were activated by the response regulator PhoB under phosphate-depleted conditions. We show that PhoB is a strong competitor against LasR and RsaL for binding to the promoter of lasI and induces significant expression of lasI, rhlR, and mvfR. However, expression of lasI, encoding the signal 3-oxo-C12-HSL, was increased only marginally under the same phosphate-depleted conditions. This seeming inconsistency was attributed to the induction of pvdQ, which encodes an enzyme for degradation of 3-oxo-C12-HSL signal molecules. Taken together, the results from this study demonstrate that through the two-component regulatory system PhoR/PhoB, phosphate depletion stress could influence the QS network by modulating several key regulators, including lasI, rhlR, mvfR, and pvdQ The findings highlight not only the potency of the PhoR/PhoB-mediated bacterial stress response mechanism but also the plasticity of the P. aeruginosa QS systems in coping with the changed environmental conditions.IMPORTANCE It is not fully understood how phosphate deficiency could influence the virulence of Pseudomonas aeruginosa through modulation of the bacterial QS systems. This report presents a systemic investigation on the impact of phosphate depletion on the hierarchy of quorum sensing systems of P. aeruginosa The results showed that phosphate stress could have an extensive impact on the QS networks of this bacterial pathogen. Among the 7 QS regulatory genes representing the 3 sets of QS systems tested, 4 were significantly upregulated by phosphate depletion stress through the PhoR/PhoB two-component regulatory system, especially the upstream QS regulatory gene lasI We also present evidence that the response regulator PhoB was a strong competitor against the las regulators LasR and RsaL for the lasI promoter, unveiling the mechanistic basis of the process by which phosphate stress could modulate the bacterial QS systems.

Highlights

The hierarchical quorum sensing (QS) systems of Pseudomonas aeruginosa, consisting of las, pqs, and rhl, coordinate the expression of bacterial virulence genes
To understand the mechanisms by which phosphate depletion stress affects the bacterial QS system, production of pyocyanin and elastase was tested in P. aeruginosa wild-type strain PAO1, the lasR in-frame deletion mutant lasR deletion mutant (LASR), the phoB in-frame deletion mutant PHOB, and the lasR/phoB double in-frame deletion mutant LASRPHOB grown in lowmsphere.asm.org 2
We found that expression of lasI, rhlR, mvfR, and pqsA presented at the lowest level in the lasR/phoB double deletion mutant LASRPHOB, especially under phosphate-depleted conditions (Fig. 3), which suggests that both LasR and PhoB are the key regulators of the bacterial QS systems

Summary

Introduction

The hierarchical quorum sensing (QS) systems of Pseudomonas aeruginosa, consisting of las, pqs, and rhl, coordinate the expression of bacterial virulence genes. We present evidence that the response regulator PhoB was a strong competitor against the las regulators LasR and RsaL for the lasI promoter, unveiling the mechanistic basis of the process by which phosphate stress could modulate the bacterial QS systems. LasR mutation does not seem to forfeit lasR-controlled functions such as expression of RhlR and production of 3-oxo-C12-HSL and PQS [4, 9] Environmental stresses such as starvation and phosphate and iron depletion are known to promote the expression of QS genes and the production of virulence factors, allowing P. aeruginosa to adapt to either acute or chronic infection conditions [10,11,12,13]. PhoB is phosphorylated on Asp (D54) by PhoR and thereafter activates the genes containing the PhoB binding site (the pho box) in their promoters

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