Cell to cell communication by autoinducing peptides in gram-positive bacteria

While intercellular communication systems in Gram-negative bacteria are often based on homoserine lactones as signalling molecules, it has been shown that autoinducing peptides are involved in intercellular communication in Gram-positive bacteria. Many of these peptides are exported by dedicated systems, posttranslationally modified in various ways, and finally sensed by other cells via membrane-located receptors that are part of two-component regulatory systems. In this way the expression of a variety of functions including virulence, genetic competence and the production of antimicrobial compounds can be modulated in a co-ordinated and cell density- and growth phase-dependent manner. Occasionally the autoinducing peptide has a dual function, such as in the case of nisin that is both a signalling pheromone involved in quorum sensing and an antimicrobial peptide. Moreover, biochemical, genetic and genomic studies have shown that bacteria may contain multiple quorum sensing systems, underlining the importance of intercellular communication. Finally, in some cases different peptides may be recognised by the same receptor, while also hybrid receptors have been constructed that respond to new peptides or show novel responses. This paper provides an overview of the characteristics of autoinducing peptide-based quorum sensing systems, their application in various gram-positive bacteria, and the discovery of new systems in natural and engineered ecosystems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quorum sensing intervened bacterial signaling: Pursuit of its cognizance and repression

Bacteria communicate within a system by means of a density dependent mechanism known as quorum sensing which regulate the metabolic and behavioral activities of a bacterial community. This sort of interaction occurs through a dialect of chemical signals called as autoinducers synthesized by bacteria. Bacterial quorum sensing occurs through various complex pathways depending upon specious diversity. Therefore the cognizance of quorum sensing mechanism will enable the regulation and thereby constrain bacterial communication. Inhibition strategies of quorum sensing are collectively called as quorum quenching; through which bacteria are incapacitated of its interaction with each other. Many virulence mechanism such as sporulation, biofilm formation, toxin production can be blocked by quorum quenching. Usually quorum quenching mechanisms can be broadly classified into enzymatic methods and non-enzymatic methods. Substantial understanding of bacterial communication and its inhibition enhances the development of novel antibacterial therapeutic drugs. In this review we have discussed the types and mechanisms of quorum sensing and various methods to inhibit and regulate density dependent bacterial communication.     

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。     

Cell-to-cell signaling in intestinal pathogens

In the conventional view of prokaryotic life, bacteria live a unicellular existence, with responses to external stimuli limited to the detection of chemical and physical signals of environmental origin. This view of bacteriology is now recognized as overly simplistic, because bacteria communicate with each other through small "hormone-like" organic compounds referred to as autoinducers (Als). These bacterial cell-to-cell signaling systems were initially described as mechanisms through which bacteria regulate gene expression via cell density, and, therefore, they have been named quorum sensing. When the Als reach a threshold concentration, they interact with regulatory proteins, thereby driving bacterial gene expression. Bacterial intercellular communication provides a mechanism for the regulation of gene expression resulting in coordinated population behavior. The functions controlled by quorum sensing are varied and reflect the needs of a particular species of bacteria inhabiting a given niche. Quorum sensing-controlled processes include bioluminescence, virulence factor expression, biofilm development, and conjugation among others. Enteric pathogens use quorum sensing to regulate genes involved in virulence, such as motility, and type III secretion. Quorum sensing is utilized to sense the presence of the normal intestinal flora and to warrant successful colonization of the host.     

粘质沙雷氏菌AS-1中SpnR功能及卤化呋喃对其群体感应的抑制

通过分泌和感知一系列信号分子,细菌能够根据自身菌体密度的变化调控基因的表达,从而控制一系列重要的表现型,包括毒力因子的产生,生物膜的形成以及菌体发光等.这种广泛存在的信号机制被称为群体感应.在沙雷氏菌种中已经发现了多套群体感应机制.粘质沙雷氏菌AS-1从土壤中分离,其中含有LuxI/LuxR的同类蛋白,被称为SpnI/SpnR.粘质沙雷氏菌AS-1合成AHLs分子N-hexanoy1-L-homoserinelactone(C6-HSL)和N-(3.oxohexanoyl)-L-homoserine lactone(3-oxo-C6-HSL)作为其信号分子,通过群体感应感知菌体密度来控制基因的表达.通过基因替代的方法制得了spnR基因破坏的变异株,命名为粘质沙雷氏菌AS-1R.对粘质沙雷氏菌AS-1R的研究表明SpnR蛋白消极的调控沙雷氏菌红色色素的产生,运动性以及生物膜的形成等一系列由群体感应控制的性状:另一方面,作为一种天然的群体感应抑制剂,卤化呋喃能够有效的抑制粘质沙雷氏菌AS-1的群体感应,但并不干扰AHL-SpnR的相互作用.为运用粘质沙雷氏菌群体感应调节抑制其致病性提供了方法和依据,同时也为卤化呋喃对群体感应抑制机理的研究提供了新的思路.     

Monitoring of Vibrio harveyi quorum sensing activity in real time during infection of brine shrimp larvae

Quorum sensing, bacterial cell-to-cell communication, has been linked to the virulence of pathogenic bacteria. Indeed, in vitro experiments have shown that many bacterial pathogens regulate the expression of virulence genes by this cell-to-cell communication process. Moreover, signal molecules have been detected in samples retrieved from infected hosts and quorum sensing disruption has been reported to result in reduced virulence in different host–pathogen systems. However, data on in vivo quorum sensing activity of pathogens during infection of a host are currently lacking. We previously reported that quorum sensing regulates the virulence of Vibrio harveyi in a standardised model system with gnotobiotic brine shrimp (Artemia franciscana) larvae. Here, we monitored quorum sensing activity in Vibrio harveyi during infection of the shrimp, using bioluminescence as a read-out. We found that wild-type Vibrio harveyi shows a strong increase in quorum sensing activity early during infection. In this respect, the bacteria behave remarkably similar in different larvae, despite the fact that only half of them survive the infection. Interestingly, when expressed per bacterial cell, Vibrio harveyi showed around 200-fold higher maximal quorum sensing-regulated bioluminescence when associated with larvae than in the culture water. Finally, the in vivo quorum sensing activity of mutants defective in the production of one of the three signal molecules is consistent with their virulence, with no detectable in vivo quorum sensing activity in AI-2- and CAI-1-deficient mutants. These results indicate that AI-2 and CAI-1 are the dominant signals during infection of brine shrimp.     

Pyrogallol and its analogs can antagonize bacterial quorum sensing in Vibrio harveyi

Bacteria can coordinate community-wide behaviors through quorum sensing, that is, the secretion and sensing of autoinducer (AI) molecules. Bacterial quorum sensing is implicated in the regulation of pathologically relevant events such as biofilm formation, bacterial virulence, and drug resistance. Inhibitors of bacterial quorum sensing could therefore be useful therapeutics. Herein we report for the first time the discovery of several pyrogallol compounds as single digit micromolar inhibitors of bacterial quorum sensing in Vibrio harveyi.     

The impact of mutations in the quorum sensing systems of Aeromonas hydrophila, Vibrio anguillarum and Vibrio harveyi on their virulence towards gnotobiotically cultured Artemia franciscana

Disruption of quorum sensing, bacterial cell-to-cell communication by means of small signal molecules, has been suggested as a new anti-infective strategy for aquaculture. However, data about the impact of quorum sensing on the virulence of aquatic pathogens are scarce. In this study, a model system using gnotobiotically cultured Artemia franciscana was developed in order to determine the impact of mutations in the quorum sensing systems of Aeromonas hydrophila, Vibrio anguillarum and V. harveyi on their virulence. Mutations in the autoinducer 2 (AI-2) synthase gene luxS, the AI-2 receptor gene luxP or the response regulator gene luxO of the dual channel quorum sensing system of V. harveyi abolished virulence of the strain towards Artemia. Moreover, the addition of an exogenous source of AI-2 could restore the virulence of an AI-2 non-producing mutant. In contrast, none of the mutations in either the acylated homoserine lactone (AHL)-mediated component of the V. harveyi system or the quorum sensing systems of Ae. hydrophila and V. anguillarum had an impact on virulence of these bacteria towards Artemia. Our results indicate that disruption of quorum sensing could be a good alternative strategy to combat infections caused by V. harveyi.     

Effects of natural and chemically synthesized furanones on quorum sensing in <Emphasis Type="Italic">Chromobacterium violaceum</Emphasis>

Background  

Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions:     

分子对接技术在研究群体感应抑制剂中的进展

在大多数致病菌中都存在群体感应系统,而群体感应抑制剂就是以此系统作为靶点,在不影响细菌生长的情况下阻断细菌生物被膜形成或抑制毒力基因表达,不易导致耐药性的产生,是一种理想的抗菌增效剂。分子对接作为虚拟筛选技术之一,其目标具体、效率高、成本低,是药物研发的重要手段。本文重点介绍了分子对接的主要模块及其在研究群体感应抑制剂中的进展。     

群体感应与微生物耐药性

微生物耐药性已成为全球关注的严重问题,其演化机制和调控机理也已成为研究热点。近年来的研究发现,一些微生物耐药性机制受到群体感应系统的调控。群体感应是一种在微生物界广泛存在并与菌体密度关联的细胞-细胞间的通讯系统。高密度的菌落群体能够产生足够数量的小分子信号,激活下游包括致病毒力和耐药性机制在内的多种细胞进程,耐受抗生素并且危害寄主。本文结合国内外最新的研究进展,对微生物群体感应系统的研究现状进行了概括性介绍,重点阐述了群体感应系统对微生物耐药性机制的调控作用,如微生物生物被膜形成和药物外排泵调控等方面的作用,并探讨了利用群体淬灭控制微生物耐药性的新策略。     

铜绿假单胞菌群体感应系统研究进展

群体感应系统是一种细胞密度依赖的基因表达系统,其广泛存在于细菌性病原体中,是细菌细胞通讯方式的一种。群体感应系统可利用细菌释放的信号分子不断监控周围细菌的密度。当细菌密度达到阈值时,群体感应系统网络将启动,参与调控生物被膜、细菌毒力等特定基因的表达,从而使临床抗感染治疗失败。而通过抑制群体感应系统,可一定程度上治疗铜绿假单胞菌引起的感染。本文通过查阅近年国内外相关文献,对铜绿假单胞菌群体感应系统研究进展进行总结,为临床铜绿假单胞菌治疗提供新的方向,即群体感应系统抑制剂有可能成为治疗铜绿假单胞菌感染的新策略。     

Resistance to Quorum-Quenching Compounds

Bacteria have the remarkable ability to communicate as a group in what has become known as quorum sensing (QS), and this trait has been associated with important bacterial phenotypes, such as virulence and biofilm formation. Bacteria also have an incredible ability to evolve resistance to all known antimicrobials. Hence, although inhibition of QS has been hailed as a means to reduce virulence in a manner that is impervious to bacterial resistance mechanisms, this approach is unlikely to be a panacea. Here we review the evidence that bacteria can evolve resistance to quorum-quenching compounds.     

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。     

Inhibition of biofilm formation and swarming of Escherichia coli by (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone

The quorum-sensing disrupter (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone (furanone) of the alga Delisea pulchra was found to inhibit the swarming motility of Escherichia coli completely at 13 microg cm-2 (also at 20 microg ml-1) but did not inhibit its growth rate at 13-52 microg cm-2 or from 20 to 100 microg ml-1. Swimming was not inhibited by the furanone at 20-40 microg ml-1. In addition, confocal scanning laser microscopy revealed that this furanone at 60 microg ml-1 inhibited the biofilm formation of E. coli, as it decreased its thickness by 55%, reduced the number of water channels and decreased the percentage of live cells by 87%. This suggests that natural furanone may be used as a new method to control bacterial biofilms that does not involve toxicity. Furanone at 10 microg ml-1 also inhibited by 3300-fold the quorum sensing of Vibrio harveyi via autoinducer 1 (AI-1) and inhibited by 5500-fold that of V. harveyi via of autoinducer 2 (AI-2) as well as inhibited by 26-600-fold the quorum sensing of E. coli via AI-2; hence, this furanone is a non-specific intercellular signal antagonist.     

Implications of endophyte-plant crosstalk in light of quorum responses for plant biotechnology

Quorum sensing, the cell-to-cell communication system mediated by autoinducers, is responsible for regulation of virulence factors, infections, invasion, colonization, biofilm formation, and antibiotic resistance within bacterial populations. Concomitantly, quorum quenching is a process that involves attenuation of virulence factors by inhibiting or degrading quorum signaling autoinducers. Survival of endophytic microorganisms, commonly known as endophytes, in planta is a continuous mêlée with invading pathogens and pests. In order to survive in their microhabitats inside plants, endophytes have co-evolved to not only utilize an arsenal of biologically active defense compounds but also impede communication between invading pathogens. Such antivirulence strategies prevent pathogens from communicating with or recognizing each other and thus, colonizing plants. The quenching phenomena often involves microbial crosstalk within single or mixed population(s) vis-à-vis gene expression, and production/modulation of quenching enzymes coupled to various antagonistic and synergistic interactions. This concept is particularly interesting because it can be biotechnologically translated in the future to quorum inhibiting antivirulence therapies without triggering resistance in bacteria, which is currently a major problem worldwide that cannot be tackled only with antimicrobial therapies. In this mini-review, we highlight the quorum quenching capacity of endophytes with respect to attenuation of virulence factors and aiding in plant defense response. Further, benefits and potential challenges of using such systems in biotechnology are discussed.     

葡萄球菌毒力调控中的群体感应系统

葡萄球菌细胞密度依赖性的多基因表达调控(群体感应)系统,是通过自身诱导与信号转导途径使其感知环境信息,调节多种毒力因子的表达。这些毒力因子的表达受agr、sae以及arl等多种基因表达系统的紧密调控,同时也受Sar家族蛋白的调节。此外,葡萄球菌毒力及抗性密切相关的生物膜形成与发育,也受群体感应系统的影响。对群体感应系统的自身诱导作用的干扰,原则上可成为寻找新型抗菌药物较适合的途径。     

细菌的信息交流

细菌与细菌之间的信息交流是通过相互交换一种自动诱导物(autoinducer)的信号分子来实现的。这种信息交换的过程被称为群体感应(quorumsystem)。细菌根据这种特定信号分子浓度的变化来监测环境中其它细菌数量的变化。细菌的群体感应系统分为种内和种间信息交流两大类。细菌间的信息交流涉及到细菌的多种生理功能,如细菌的致病能力等。因此研究细菌间的信息交流有可能找到一条新的防治细菌感染途径。     

Quorum sensing signals are produced by Aeromonas salmonicida and quorum sensing inhibitors can reduce production of a potential virulence factor

Many pathogens control production of virulence factors by self-produced signals in a process called quorum sensing (QS). We demonstrate that acyl homoserine lactone (AHL) signals, which enable bacteria to express certain phenotypes in relation to cell density, are produced by a wide spectrum of Aeromonas salmonicida strains. All 31 typical strains were AHL producers as were 21 of 26 atypical strains, but on a strain population basis, production of virulence factors such as protease, lipase, A-layer or pigment did not correlate with the production and accumulation of AHLs in the growth medium. Pigment production was only observed in broth under highly aerated conditions. Quorum sensing inhibitors (QSIs) are compounds that specifically block QS systems without affecting bacterial growth and 2 such compounds, sulphur-containing AHL-analogues, reduced production of protease in a typical strain of Aeromonas salmonicida. The most efficient compound N-(heptylsulfanylacetyl)-L-homoserine lactone (HepS-AHL), reduced protease production by a factor of 10. Five extracellular proteases were detected on gelatin-containing sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) gels and 3 of these were completely down regulated by HepS-AHL. Hence, QSIs can curb virulence in some strains and could potentially be pursued as bacterial disease control measures in aquaculture.