噬菌体群体感应系统及其分子机理研究进展

群体感应(Quorum Sensing,QS)是微生物群体在生长过程中,随着群体密度的增加,其分泌的"信号分子"的浓度达到一定阈值后与微生物体内特定受体结合,从而影响微生物特定基因表达,导致其生理和生化特性的变化,表现出少量菌体或单个菌体所不具备的特征。1994年Fuqua提出群体感应概念后就成为微生物领域的研究热点。然而,群体感应的研究主要集中在细菌中,但近年来群体感应在噬菌体、真菌中也不断被发现,尤其自2017年Erez在多种枯草芽孢杆菌噬菌体中发现群体感应现象,并且揭示噬菌体群体感应主要调控其溶源-裂解途径的转换。近年来的研究又陆续在其他噬菌体中发现了群体感应。本文综述了噬菌体群体感应系统最新研究进展及其相关的基因功能和分子机理。     

细菌群体感应系统与噬菌体的相互作用机制研究进展

细菌在与噬菌体的长期共进化过程中形成多种抵抗噬菌体侵染的机制,其中群体感应参与的细菌抵御噬菌体侵染机制成为近年来的研究热点。群体感应与噬菌体之间的相互作用是复杂和多样的,本文将重点综述群体感应在噬菌体侵染中的作用、调控在噬菌体裂解-溶源转变的作用,以及群体感应与噬菌体的其他相互影响等内容,为噬菌体在细菌性疾病的治疗提供理论依据。     

Disruption of bacterial quorum sensing by other organisms

Higher plants and algae produce compounds that mimic quorum sensing: signals used by bacteria to regulate the expression of many genes and behaviors. Similarly, various bacteria can stimulate, inhibit or inactivate quorum sensing in other bacteria. These discoveries offer new opportunities to manipulate bacterial quorum sensing in applications relevant to medicine, agriculture and the environment.     

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。     

Vibrio fischeri uses two quorum-sensing systems for the regulation of early and late colonization factors

Vibrio fischeri possesses two quorum-sensing systems, ain and lux, using acyl homoserine lactones as signaling molecules. We have demonstrated previously that the ain system activates luminescence gene expression at lower cell densities than those required for lux system activation and that both systems are essential for persistent colonization of the squid host, Euprymna scolopes. Here, we asked whether the relative contributions of the two systems are also important at different colonization stages. Inactivation of ain, but not lux, quorum-sensing genes delayed initiation of the symbiotic relationship. In addition, our data suggest that lux quorum sensing is not fully active in the early stages of colonization, implying that this system is not required until later in the symbiosis. The V. fischeri luxI mutant does not express detectable light levels in symbiosis yet initiates colonization as well as the wild type, suggesting that ain quorum sensing regulates colonization factors other than luminescence. We used a recently developed V. fischeri microarray to identify genes that are controlled by ain quorum sensing and could be responsible for the initiation defect. We found 30 differentially regulated genes, including the repression of a number of motility genes. Consistent with these data, ain quorum-sensing mutants displayed an altered motility behavior in vitro. Taken together, these data suggest that the sequential activation of these two quorum-sensing systems with increasing cell density allows the specific regulation of early colonization factors (e.g., motility) by ain quorum sensing, whereas late colonization factors (e.g., luminescence) are preferentially regulated by lux quorum sensing.     

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。     

群体感应在生物强化功能菌定殖及降解能力增强中的作用研究进展

由于难降解有机污染物和外界环境对水处理系统的冲击干扰,污水水质常出现不达标现象。引入外源含有相关功能基因并且具有基因水平转移能力的工程菌株进行生物强化处理是提高污水处理效能的有效措施。污水处理系统中存在能够分泌信号分子的菌体,菌间具有群体感应现象,当种群密度达到感应阈值时,菌体会通过释放信号分子来触发一些群体行为,从而激活相关基因的表达(如生物膜形成、生物发光、抗生素合成和毒力因子表达等)。早期的群体感应技术研究主要集中在信号传递学、微生物社会行为学和医学微生物领域,近年来,在水处理领域也开始有相继报道,研究表明群体感应在污水生物处理中发挥重要作用,并且影响生物强化菌株的定殖和污染物降解,因此群体感应行为调控是生物强化技术成效显著与否的关键因素。本文综述了群体感应及信号分子的作用机制、信号分子释放及存在的影响因素以及群体感应对菌株定殖、微生物群落结构和污染物去除的影响,并对从群体感应角度出发研究生物强化过程进行了展望,旨在为生物强化技术的有效实施及提升污水处理效能提供一种新思路,为深入理解生物强化过程中群体感应调控行为提供理论参考。     

The effect of Quorum sensing inhibitors on the evolution of CRISPR-based phage immunity in Pseudomonas aeruginosa

Quorum sensing controls the expression of a wide range of important traits in the opportunistic pathogen Pseudomonas aeruginosa, including the expression of virulence genes and its CRISPR-cas immune system, which protects from bacteriophage (phage) infection. This finding has led to the speculation that synthetic quorum sensing inhibitors could be used to limit the evolution of CRISPR immunity during phage therapy. Here we use experimental evolution to explore if and how a quorum sensing inhibitor influences the population and evolutionary dynamics of P. aeruginosa upon phage DMS3vir infection. We find that chemical inhibition of quorum sensing decreases phage adsorption rates due to downregulation of the Type IV pilus, which causes delayed lysis of bacterial cultures and favours the evolution of CRISPR immunity. Our data therefore suggest that inhibiting quorum sensing may reduce rather than improve the therapeutic efficacy of pilus-specific phage, and this is likely a general feature when phage receptors are positively regulated by quorum sensing.Subject terms: Microbiology, Antimicrobials     

The LuxR homolog ExpR, in combination with the Sin quorum sensing system, plays a central role in Sinorhizobium meliloti gene expression

Quorum sensing, a population density-dependent mechanism for bacterial communication and gene regulation, plays a crucial role in the symbiosis between alfalfa and its symbiont Sinorhizobium meliloti. The Sin system, one of three quorum sensing systems present in S. meliloti, controls the production of the symbiotically active exopolysaccharide EPS II. Based on DNA microarray data, the Sin system also seems to regulate a multitude of S. meliloti genes, including genes that participate in low-molecular-weight succinoglycan production, motility, and chemotaxis, as well as other cellular processes. Most of the regulation by the Sin system is dependent on the presence of the ExpR regulator, a LuxR homolog. Gene expression profiling data indicate that ExpR participates in additional cellular processes that include nitrogen fixation, metabolism, and metal transport. Based on our microarray analysis we propose a model for the regulation of gene expression by the Sin/ExpR quorum sensing system and another possible quorum sensing system(s) in S. meliloti.     

Gene dosage compensation calibrates four regulatory RNAs to control Vibrio cholerae quorum sensing

Quorum sensing is a mechanism of cell‐to‐cell communication that allows bacteria to coordinately regulate gene expression in response to changes in cell‐population density. At the core of the Vibrio cholerae quorum‐sensing signal transduction pathway reside four homologous small RNAs (sRNAs), named the quorum regulatory RNAs 1–4 (Qrr1–4). The four Qrr sRNAs are functionally redundant. That is, expression of any one of them is sufficient for wild‐type quorum‐sensing behaviour. Here, we show that the combined action of two feedback loops, one involving the sRNA‐activator LuxO and one involving the sRNA‐target HapR, promotes gene dosage compensation between the four qrr genes. Gene dosage compensation adjusts the total Qrr1–4 sRNA pool and provides the molecular mechanism underlying sRNA redundancy. The dosage compensation mechanism is exquisitely sensitive to small perturbations in Qrr levels. Precisely maintained Qrr levels are required to direct the proper timing and correct patterns of expression of quorum‐sensing‐regulated target genes.     

RND家族外排泵及其与微生物群体感应系统的相互关系

抗生素耐药性一直是细菌病害防治的难题,药物外排泵过量表达是细菌耐药性形成的重要机制之一。在革兰氏阴性细菌中,RND(Resistance-nodulation-cell division)家族外排泵在耐药性中发挥着重要作用,近年来的研究表明,依赖于小分子信号物质进行调控的群体感应系统与RND外排泵家族之间存在紧密的相互作用关系。本文在介绍RND家族外排泵的结构、转运机理和群体感应系统的类型及调控方式的基础上,剖析了群体感应系统对RND外排泵的调控机理以及RND外排泵对群体感应系统信号分子转运的影响。深入研究RND家族外排泵与群体感应系统之间的相互依赖、相互制约关系有利于阐明RND家族外排泵的调控机理,并有可能为克服微生物耐药性问题提供新的思路。     

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.