Degradation of N-Acyl Homoserine Lactone Quorum Sensing Signals by Bacillus thuringiensis AHL Lactonase

Bacterial cells rely on signaling molecules to communicate with others from the same species and induce certain genes in a process known as quorum sensing (QS). A common molecule is N-acyl homoserine lactone (AHL) which is responsible for the expression of virulence and other factors that allow the organisms to compete in a given environment. On the other hand, other bacteria produce certain enzymes such as AHL-lactonase that break down AHL molecules and prevent gene expression of these factors. The aim of this work was to examine the level of degradation of AHL molecules by AHL-lactonase in 62 Bacillus thuringiensis (Bt) strains isolated from Middle Tennessee, Mississippi, and Alabama. N-hexanoyl-homoserine lactone (C6-HSL) and N-3-oxo-hexanoyl homoserine lactone (3-oxo-C6-HSL), which cause Chromobacterium violaceum (CV026) to produce a purple pigment were tested at different concentrations to view the Bt lactonase activity. In addition, PCR was used to test for the presence of the lactonase gene. The results showed that among the 62 Bt strains, there were 58 that possessed the AHL-lactonase (aiiA) gene and 48 strains were able to degrade C6-HSL. At high concentrations of AHL, only 13 strains were able to completely degrade C6-HSL. In addition, degradation of 3-oxo-C6-HSL was weak compared to C6-HSL. The results also revealed that AHL lactonase was thermostable, and it was concluded that the level of degradation varies in Bt strains. Only 13 of the strains studied have potent inhibitory activity against C6-HSL, which may be good to be used in field applications to control agricultural pest.

P_(luxI)mutants with different promoting period and their application for quorum sensing regulated protein expression

Quorum sensing(QS)system can dynamically control the expression of proteins along with the cell growth.The promoting period of QS system has been little focused on until now.In this study,a self-induced dynamic regulated expression(SIDRE)system was constructed in Escherichia coli.To enable the system suitable for the expression of enzymes,promoter engineering was used to obtain P_(luxI)mutants.To test the SIDRE system,alginate lyase AL493 and esterase Est7 were used as target protein for expression.The enzyme activity of alginate lyase and esterase reached 96.38%and 106.71%of the control strains containing the T7 promoter.In high-density fermentation,the activity of alginate lyase expressed by the SIDRE system with P_(luxI)(T-38C)as promoter was 4.34-fold of that expressed by the T7 promoter.Therefore,the P_(luxI)mutants with different promoting periods and/or different strengths show great potential in both laboratory and industrial scale for protein expression.

Anti-Biofilm, Anti-Quorum Sensing, and Anti-Proliferative Activities of Methanolic and Aqueous Roots Extracts of Carica papaya L. and Cocos nucifera L.

Objective: This study focused on the antibacterial and anti-proliferative activity of extracts from Carica papaya and Cocos nucifera roots. Methodology: The minimum inhibitory concentration and the minimum bactericidal concentration of the extracts on Escherichia coli, Pseudomonas aeruginosa, Streptococcus mutans, and Staphylococcus aureus were deduced by the microdilution method. The anti-biofilm activity was determined on all four strains and anti-quorum sensing activity by inhibition of violacein production in Chromobacterium violaceum. Anti-proliferative activity on prostate cultured cancer cells was evaluated by MTT assay. Sterols and triterpenes were also assayed in this study. Results: The methanolic extract of Carica papaya showed the best anti-biofilm effect with a percentage inhibition of 66.10 ± 1.79. The methanolic extract of Cocos nucifera had the strongest inhibition on the production of quorum sensing (61.42 ± 0.28). In addition, the methanolic extract of Cocos nucifera roots showed the best cytotoxic effect on prostate cancer LNCaP cell lines (IC50 = 26.98 ± 2.6 μg/mL) and Carica papaya on the PC-3 lines (IC50 = 127.20 ± 5.99 μg/mL). The extracts were also rich in triterpenes and sterols. Conclusion: This study provides support for the ethnomedical use of Carica papaya and Cocos nucifera roots as an antimicrobial and anticancer.

门限Byzantine quorum系统及其在分布式存储中的应用

针对纠删编码和门限方案在分布式存储中的应用,提出门限Byzantine quorum系统(TBQS)的概念.该系统与数据分离算法相结合,可以构造可靠性较强的存储系统,当故障服务器个数不超过服务器总数的1/4时,利用TBQS设计存储策略可以实现容错和无间断服务.讨论了TBQS的存在性,构造了两类TBQS并对其效率进行分析,在此基础上设计了基于TBQS的分布式读写协议.

细菌的群体行为调控机制-Quorum sensing

群体效应 (Quorumsensing)是近来日益受到广泛关注的一种细菌群体行为调控机制 ,很多细菌有这种能力 ,即分泌一种或多种自诱导剂 (Autoinducer) ,细菌通过感应这些自诱导剂来判断菌群密度和周围环境变化 ,当菌群数达到一定的阀值 (quorum ,菌落或集落数 )后 ,启动相应一系列基因的调节表达 ,以调节菌体的群体行为。不同类型的细菌具有不同的群体效应调节系统 ,很多细菌分泌同一种诱导剂 ,以此调控不同种类细菌间的作用行为。群体效应系统在自诱导剂与受体之间存在专一性 ,同时又在调节基因和信号传递系统中体现出多样性和复杂性。由于不少人或植物的病原菌的致病机制等受群体效应的调控 。

基于Quorum系统的分布式访问控制框架研究

从通用访问控制系统出发,提出以quorum系统来设计访问控制框架,给出了基于互斥协议的quorum分布式访问控制系统(MQ-DACS),以在保持高效率的情况下,提高访问控制决策的稳定性和安全性。进一步分析了在系统结点不可靠的环境中,系统能并行执行的访问控制容量同系统可用性之间的关系,并给出了最佳方案的选取依据。

纠错码拜占庭容错Quorum中错误检测机制

在大规模存储系统中,拜占庭存储节点的容错显得越来越重要。传统拜占庭Quorum通过复制可以容忍拜占庭失效,但是它们有两个主要缺点:低的存储空间利用率和静态quorum参数。我们提出纠错码拜占庭容错Quo-rum(Erasure-code Byzantine Fault-tolerance Quorum,E-BFQ),E-BFQ采用纠错码作为冗余策略,可以提供高可靠性,同时比复制占用更少存储空间。通过客户端读/写操作和管理器诊断操作,E-BFQ可以检测拜占庭节点,动态调整系统规模和故障阈值。结果显示本文方法可以达到动态调整的目的。

基于Quorum的低占空比WSNs最优延迟可靠路由算法

在无线传感器网络中,异步低占空比技术可以极大地降低能耗,但是由于节点的低占空比唤醒会造成极大的端到端数据时延。针对这个问题提出一种基于Quorum的异步自适应低占空比路由算法ORDA(Optimal-Reliable delay routing algorithm for low duty cycle WSNs based on Quorum),将异步占空比网络和实际链路模型相结合,在异步占空比网络中节点在不同时刻的邻居发现延迟也在不断变化。首先为每个节点根据网络负载选择自身的Quorum类型,并利用Quorum特性来计算邻居节点的重叠时隙个数;然后根据链路质量进一步计算出这一跳范围内邻居节点间的成功转发预期值,并在即将唤醒的节点中选择更可靠的节点转发数据。仿真实验证明,该算法不仅能够降低端到端延迟,而且能获得很好的转发成功率。

面向云存储安全的可自愈拜占庭Quorum系统

针对云存储系统中的数据安全问题,提出了一种面向云存储安全的可自愈拜占庭Quorum系统.该系统以虚拟机作为后端存储设备构建虚拟存储节点,利用虚拟机多样化操作系统,以及动态迁移、快速部署等机制构建动态异构的存储系统架构.在拜占庭容错门限的基础上,提出自愈门限的概念,并设计相应系统安全协议,实现存储节点的自动化异常检测和状态复原.实验结果表明,提出的云存储系统具有较高的鲁棒性,能有效提高存储数据的安全性.

AGQ-MAC:无线传感器网络中基于Grid Quorum的异步低占空比MAC协议

针对无线传感器网络占空比MAC协议在链路或节点失效环境下易导致严重的能量浪费问题,提出了一种基于Grid Quorum的异步低占空比M AC协议-AGQ-M AC(Asynchronous Grid Quorum M AC).AGQ-M AC采用Grid Quorum组分配信道,通过动态调配Quorum比率得到了节点的最优占空比,并在邻节点发现过程中采用双前导序文抽样来监测信道状态,以减少节点唤醒时间从而达到能量高效.仿真实验结果表明,与其他占空比MAC协议相比,AGQ-MAC延长了网络生存时间,降低了网络能耗,提高了邻发现数据传输率,同时保持较低的平均邻发现延迟.

细菌感染性疾病中的对立统一规律与Quorum Sensing系统

引起人类细菌性感染的病原菌可以分为条件致病菌和非条件致病菌,不同性质的细菌引起的感染决定了感染矛盾的特殊性,对于不同质的矛盾,只有用不同质的方法才能解决。抗生素的发明和使用为人类控制感染性疾病的同时,这种单纯的“对抗”的解决方法也引出了一些新的矛盾。因此,细菌感染矛盾的特殊性决定我们不能采用千篇一律的“对抗斗争”形式,而必须寻求一种特殊的解决方式。对QS系统的研究发现在细菌表现致病性过程中发挥重要作用,通过QS系统减弱细菌的致病性而不杀死细菌的“抗致病性药物”来治疗感染成为一种新的抗感染思路,这种“抗致病性”概念使我们抗感染的态度从与细菌“对抗”转变为“共生”,因而QS系统可以为这种特殊矛盾提供一个合理的解决方式。

一种基于Quorum系统的异步传感网局部时间分配算法

为了在无线传感器网络中增强节点通信时间分配的公平性,设计了一种局部的按需异步时间分配算法(SATA).SATA算法的设计基于Quorum系统(Quorum system,QS).首先构造出一个QS,然后节点根据自身的通信量在QS中选择合适数量的活动时隙,并通知其邻居节点,这样可以消除信道竞争,保证每对相邻节点能够拥有适当的公共活动时隙来完成通信的需求.由于所构造的QS满足旋转封闭性,所以即使在节点时钟不准确并且不使用时间同步协议的情况下,SATA也能够保证网络的连通性.理论分析和实验验证表明,SATA能够提高信道利用率、节省能耗以及提高网络吞吐量.

Screening strategies for quorum sensing inhibitors in combating bacterial infections

Interference with quorum sensing(QS)represents an antivirulence strategy with a significant promise for the treatment of bacterial infections and a new approach to restoring antibiotic tolerance.Over the past two decades,a novel series of studies have reported that quorum quenching approaches and the discovery of quorum sensing inhibitors(QSIs)have a strong impact on the discovery of anti-infective drugs against various types of bacteria.The discovery of QSI was demonstrated to be an appropriate strategy to expand the anti-infective therapeutic approaches to complement classical antibiotics and antimicrobial agents.For the discovery of QSIs,diverse approaches exist and develop in-step with the scale of screening as well as specific QS systems.This review highlights the latest findings in strategies and methodologies for QSI screening,involving activity-based screening with bioassays,chemical methods to seek bacterial QS pathways for QSI discovery,virtual screening for QSI screening,and other potential tools for interpreting QS signaling,which are innovative routes for future efforts to discover additional QSIs to combat bacterial infections.

Inhibition of quorum sensing in Chromobacterium violaceum by Syzygium cumini L.and Pimenta dioica L.

Objective:To investigated into the anti-quorum sensing(QS)activity of Syzygium cumini L.(S.cumini)and Pimenta dioica L.(P.dioica)using Chromobacterium violaceum(C.violaceum)strains.Methods:In this study,anti-QS activity of ethanol extract of Syzygium cumini L.and Pimenta dioica L.were screened using C.violaceum CV026 biosensor bioassay.By bioassay guided fractionation of 5.cumini and P.dioica,ethyl acetate fraction(EAF)with strong anti-QS activity was separated.Inhibition of QS regulated violacein production in C.violaceum ATCC12472 by EAF was assessed at different concentrations.The effect of EAF on the synthesis of autoinducer like N-acyl homoserine lactone(AHL)was studied in C.violaceum ATCC31532 using its mutant C.violaceum CV026 by standard methods.Results:EAF inhibited violacein production in C.violaceum ATCC12472 in a concentration dependent manner without significant reduction in bacterial growth.Complete inhibition of violacein production was evidenced in 0.75-1.0 mg/mL concentration of EAF without inhibiting the synthesis of the AHL.TLC biosensor overlay profile of EAF revealed two translucent spots in 5.cumini and P.dioica that inhibited C_6-AHL mediated violacein production in C.violaceum CV026.Conclusions:This study indicates the anti-QS activity of the tested medicinal plants against C.violaceum.

入侵容忍的Quorum系统及其可生存性分析

针对入侵容忍系统的一致性问题,提出一种基于Quorum结构的系统构建方法。以可信实时计算基为平台,采用同步和异步混合的时间模型,实现了客户端的读写协议、服务器的数据更新协议和数据复制协议。构造了入侵容忍的对称Quorum系统、对称网格Quorum系统和非对称Quorum系统,从系统预期失效时间的角度分析了3种入侵容忍Quorum系统的可生存性,得出预期失效时间变化趋势与门限值、系统规模之间的关系。与其他Quorum系统相比,在规模相同的情况下,提出的非对称入侵容忍Quorum系统的可生存性最高,高于f屏蔽Quorum系统,对称网格入侵容忍Quorum系统的可生存性高于常规网格Quorum系统。

Quorum-Sensing of Bacteria and Its Application

Quorum sensing, or auto induction, as a cell density dependent signaling mechanism in many microorganisms, is trig- gered via auto inducers which passively diffuse across the bacterial envelope and therefore intracellulaly accumulate only at higher bacterial densities to regulate specialized processes such as genetic competence, bioluminescence, virulence and sporulation. N-acyl homoserine lactones are the most common type of signal molecules. Aquaculture is one of the fastest-growing food-producing indus- tries, but disease outbreaks caused by pathogenic bacteria are a significant constraint on the development of the sector worldwide. Many of these pathogens have been found to be controlled by their quorum sensing systems. As there is relevance between the pathogenic bacteria＇s virulence factor expression and their auto inducers, quorum quenching is a new effective anti-infective strategy to control infections caused by bacterial pathogens in aquaculture. The techniques used to do this mainly include the following： （1） the inhibition of signal molecule biosynthesis, （2） blocking signal transduction, and （3） chemical inactivation and biodegradation of signal molecules. To provide a basis for finding alternative means of controlling aquatic diseases by quorum quenching instead of treatment by antibiotics and disinfectants, we will discuss the examination, purification and identification of auto inducers in this paper.

基于Quorum系统容错技术综述

Quorum系统是一种新型冗余拓扑的集合系统 在“冗余”设计的基础上 ,quorum通过交叉的结点把有效数据复制到其他quorum的结点中 ,增加了Quorum系统数据冗余性 当某些结点发生故障或者错误时 ,通过选举协议 ,从含有故障结点 quorum的有效结点中选举出有效数据 ;或者采用互斥协议 ,从不含故障或者错误结点的有效quorum的结点中获得有效数据 ,系统仍能可靠运行 分析了各种Quorum系统的容错方式、性能比较 ,探讨了Quorum系统发展中需要改进的关键问题 。

无线Mesh网中的Quorum节能机制

无线Mesh网络节能问题十分重要。文章讨论的基于Quorum的节能机制对网络规模、节点密度、移动性和多跳等因素不敏感,非常适合无线Mesh网络。Quorum节能机制主要基于MANET网络环境设计。Quorum系统根据时钟同步的难易程度,可以应用于同步和异步两种工作模式。目前对Quorum节能系统的研究主要集中在能量效率优化和自适应系统方面。对于异步和同步两种模式的协同,基于Quorum机制的节能与功率控制、MAC路由结合的跨层设计,是值得尝试的课题。

无线Ad hoc网络中基于Quorum系统的异步节能机制改进

无线Ad hoc网络是一种没有外界能量补给的自组织网络,网络中每一个节点都靠最初的能量储备来维持,因此,节能便成为至关重要的问题。基于Quorum分布式系统提出的节能机制,其核心思想是使节点的激活时隙成为一种特定的分布,保证互相之间的时隙有交叠,从而使得通信的两个节点能够监听到对方。本文将介绍在无线Ad hoc网络中传统的同步方式面临的挑战,前人对基于Quorum的异步节能机制所做的工作,最后提出一种"Dgrid"自适应的异步节能机制。

The Mechanisms and Applications of Quorum Sensing(QS) and Quorum Quenching(QQ)

Quorum sensing(QS)is a regulatory system that regulates the behavior of microbial populations by sensing the concentration of signal molecules that are spontaneously produced and released by bacteria.The strategy of blocking the QS system and inhibiting the production of virulence factors is termed as quorum quenching(QQ).This strategy attenuates virulence without killing the pathogens,thereby weakening the selective pressure on pathogens and postponing the evolution of QQ-mediated drug resistance.In recent years,there have been significant theoretical and practical developments in the field of QS and QQ.In particular,with the development and utilization of marine resources,more and more marine microbial species have been found to be regulated by these two mechanisms,further promoting the research progress of QS and QQ.In this review,we described the diversity of QS signals and QS-related regulatory systems,and then introduced mechanisms related to QS interference,with particular emphasis on the description of natural QQ enzymes and chemicals acting as QS inhibitors.Finally,the exploitation of quorum sensing quenchers and the practical application of QQ were introduced,while some QQ strategies were proposed as promising tools in different fields such as medicine,aquaculture,agriculture and biological pollution prevention areas.