Identification of a novel regulator of the quorum-sensing systems in Pseudomonas aeruginosa

Quorum sensing is a global gene-regulatory mechanism in bacteria that enables individual bacterial cells to communicate and coordinate their population behaviors. Quorum sensing is central to the pathogenesis of many bacterial pathogens including Pseudomonas aeruginosa and therefore has been exploited as a target for developing novel antipathogenic drugs. In P. aeruginosa , three intertwined quorum-sensing systems, las, rhl , and the 2-alkyl-4(1 H )-quinolone system, which includes the Pseudomonas quinolone signal (PQS), control virulence factor production, and pathogenesis processes. Previously, we obtained a mutant with diminished expression of the phzA1B1C1D1E1F1G1 operon that is involved in the production of virulence factor phenazine compounds. In this study, the mutant was further characterized, and evidence indicating that the disrupted gene PA1196 in the mutant is a potential regulator of the rhl and PQS systems is presented. PA1196 positively controls the expression of the rhl and PQS systems and affects bacterial motility and multiple virulence factor expression via the quorum-sensing systems. This adds an important new player in the complex quorum-sensing network in P. aeruginosa .     

The influence of iron on Pseudomonas aeruginosa physiology: a regulatory link between iron and quorum sensing

In iron-replete environments, the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein represses expression of two small regulatory RNAs encoded by prrF1 and prrF2. Here we describe the effects of iron and PrrF regulation on P. aeruginosa physiology. We show that PrrF represses genes encoding enzymes for the degradation of anthranilate (i.e. antABC), a precursor of the Pseudomonas quinolone signal (PQS). Under iron-limiting conditions, PQS production was greatly decreased in a DeltaprrF1,2 mutant as compared with wild type. The addition of anthranilate to the growth medium restored PQS production to the DeltaprrF1,2 mutant, indicating that its defect in PQS production is a consequence of anthranilate degradation. PA2511 was shown to encode an anthranilate-dependent activator of the ant genes and was subsequently renamed antR. AntR was not required for regulation of antA by PrrF but was required for optimal iron activation of antA. Furthermore, iron was capable of activating both antA and antR in a DeltaprrF1,2 mutant, indicating the presence of two distinct yet overlapping pathways for iron activation of antA (AntR-dependent and PrrF-dependent). Additionally, several quorum-sensing regulators, including PqsR, influenced antA expression, demonstrating that regulation of anthranilate metabolism is intimately woven into the quorum-sensing network of P. aeruginosa. Overall, our data illustrate the extensive control that both iron regulation and quorum sensing exercise in basic cellular physiology, underlining how intermediary metabolism can affect the regulation of virulence factors in P. aeruginosa.     

GeneChip expression analysis of the VqsR regulon of Pseudomonas aeruginosa TB

Two interlinked quorum sensing circuits, las and rhl, which control pathogenesis of Pseudomonas aeruginosa are further modulated by numerous regulators, including VqsR (virulence and quorum sensing regulator). High-density oligonucleotide microarrays were used to compare the global expression profile of a wild-type and VqsR mutant in ABC minimal medium. The expression of a large group of metabolic genes, ECF sigma factors as well as of many quorum-sensing genes previously not assigned to VqsR-regulon was found to be affected by the disruption of vqsR.     

喹诺酮信号系统研究进展

喹诺酮信号系统是铜绿假单胞菌群体感应调控网络中一个重要组成部分,对于绿脓菌素和弹性蛋白酶等毒力因子的表达及细菌生物被膜形成和细菌运动具有重要的调控作用,因此与临床细菌感染密切相关。3,4-二羟基-2-庚基-喹诺酮(Pseudomonas quinolone signal,PQS)及2-庚基-4喹诺酮(4-hydroxy-2-heptylquinoline,HHQ)是pqs调控系统中重要的信号分子。PQS对于细菌在压力下群体密度及细菌物质运输具有调控作用,从而增强细菌对于环境的适应能力。同时PQS等分子在一定程度上抑制了人体的免疫系统,帮助细菌在宿主体内生存。HHQ在其他革兰氏阴性细菌及革兰氏阳性细菌中也有合成并发挥调控作用,所以喹诺酮信号分子不仅是种内也是种间交流媒介。将喹诺酮系统作为靶点降低细菌的信号交流是抑制细菌感染的一个新思路。本文对喹诺酮信号系统进行概述。     

Pseudomonas aeruginosa virulence analyzed in a Dictyostelium discoideum host system

Pseudomonas aeruginosa is an important opportunistic pathogen that produces a variety of cell-associated and secreted virulence factors. P. aeruginosa infections are difficult to treat effectively because of the rapid emergence of antibiotic-resistant strains. In this study, we analyzed whether the amoeba Dictyostelium discoideum can be used as a simple model system to analyze the virulence of P. aeruginosa strains. The virulent wild-type strain PAO1 was shown to inhibit growth of D. discoideum. Isogenic mutants deficient in the las quorum-sensing system were almost as inhibitory as the wild type, while rhl quorum-sensing mutants permitted growth of Dictyostelium cells. Therefore, in this model system, factors controlled by the rhl quorum-sensing system were found to play a central role. Among these, rhamnolipids secreted by the wild-type strain PAO1 could induce fast lysis of D. discoideum cells. By using this simple model system, we predicted that certain antibiotic-resistant mutants of P. aeruginosa should show reduced virulence. This result was confirmed in a rat model of acute pneumonia. Thus, D. discoideum could be used as a simple nonmammalian host system to assess pathogenicity of P. aeruginosa.     

铜绿假单胞菌中一个新的吩嗪合成调节基因

[目的]在次抑制浓度四环素条件下,研究铜绿假单胞菌phzAl操纵子的调节基因及调节途径.[方法]对转座突变库中phaAl操纵子表达发生变化的突变体,进行随机PCR、基因测序及比对,确定突变位点.并以发光杆菌的荧光素酶基因操纵子luxCDABE为报道基因,研究基因调节作用及调节路径.[结果]在两株突变体PAM0487和PAM0487R中phzAl操纵子的表达降低,这两株突变体的突变基因确定为假定钼元素转运蛋白调节子PA0487基因.[结论]PA0487是phzAl操纵子表达的一个新的正向调节子,并对密度感应系统相关基因的表达有凋节作用.