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。     

PqsD is responsible for the synthesis of 2,4-dihydroxyquinoline, an extracellular metabolite produced by Pseudomonas aeruginosa

2,4-Dihydroxyquinoline (DHQ) is an abundant extracellular metabolite of the opportunistic pathogen Pseudomonas aeruginosa that is secreted into growth medium in stationary phase to concentrations comparable with those of the Pseudomonas quinolone signal. Using a combination of biochemical and genetic approaches, we show that PqsD, a condensing enzyme in the pqs operon that is essential for Pseudomonas quinolone signal synthesis, accounts for DHQ formation in vivo. First, the anthraniloyl moiety is transferred to the active-site Cys of PqsD to form an anthraniloyl-PqsD intermediate, which then condenses with either malonyl-CoA or malonyl-acyl carrier protein to produce 3-(2-aminophenyl)-3-oxopropanoyl-CoA. This short-lived intermediate undergoes an intramolecular rearrangement to form DHQ. DHQ was produced by Escherichia coli coexpressing PqsA and PqsD, illustrating that these two proteins are the only factors necessary for DHQ synthesis. Thus, PqsD is responsible for the production of DHQ in P. aeruginosa.     

植物精油对铜绿假单胞菌群体感应系统的抑制作用研究进展

群体感应（quorum sensing,QS）是细菌个体与个体之间的一种交流机制,广泛存在于细菌中。铜绿假单胞菌是人类的一种条件致病菌,它具有至少3种QS系统,即las、rhl和pqs系统,且各系统之间存在着级联调控关系,它们共同作用调控着该菌众多毒力基因的表达和毒力因子的产生。近年来,通过抑制铜绿假单胞菌的QS系统以控制其毒力和致病力,成为一种新型的铜绿假单胞菌感染防控策略。植物精油是一种天然的群体感应抑制剂（quorum sensing inhibitors, QSI）,多种精油活性化合物都能抑制铜绿假单胞菌的QS系统,而且尚未发现细菌对其产生耐药性。基于此,梳理了铜绿假单胞菌QS系统的组成及其级联调控关系,简要介绍了植物精油的QS抑制机制和抑制活性,并重点综述了萜烯类化合物、芳香族化合物、脂肪族化合物、含硫含氮化合物4类精油化合物对铜绿假单胞菌QS系统抑制作用的研究进展,以期为从天然化合物中发现和筛选安全、高效的细菌QSI的相关研究提供参考,并为致病菌的防控奠定理论基础。     

The small RNA PhrS stimulates synthesis of the Pseudomonas aeruginosa quinolone signal

Quorum sensing, a cell-to-cell communication system based on small signal molecules, is employed by the human pathogen Pseudomonas aeruginosa to regulate virulence and biofilm development. Moreover, regulation by small trans-encoded RNAs has become a focal issue in studies of virulence gene expression of bacterial pathogens. In this study, we have identified the small RNA PhrS as an activator of PqsR synthesis, one of the key quorum-sensing regulators in P. aeruginosa. Genetic studies revealed a novel mode of regulation by a sRNA, whereby PhrS uses a base-pairing mechanism to activate a short upstream open reading frame to which the pqsR gene is translationally coupled. Expression of phrS requires the oxygen-responsive regulator ANR. Thus, PhrS is the first bacterial sRNA that provides a regulatory link between oxygen availability and quorum sensing, which may impact on oxygen-limited growth in P. aeruginosa biofilms.     

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.     

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 .     

Quorum sensing: dynamic response of Pseudomonas aeruginosa to external signals

A recent study suggests that the opportunistic pathogen Pseudomonas aeruginosa can actively monitor the host immune system. The P. aeruginosa outer membrane protein OprF was found to bind specifically to the cytokine interferon-gamma (IFN-gamma), and this interaction upregulated production of virulence factors through a cell-cell communication system known as quorum sensing (QS). Taken together with previous findings that P. aeruginosa QS can alter the host immune response (e.g. by activation of IFN-gamma), these data illustrate an exciting new element of bacteria-host interactions in which the P. aeruginosa quorum-sensing system both senses and modulates the host immune state.