真菌中的群体感应系统

以胞间通讯信号分子介导的细菌群体感应参与细菌多种生理功能的调控是非常普遍的。近年的研究表明,真菌中也存在类似于细菌群体感应信号分子的调节分子,并且介导着真菌某些生理行为的调节。这一过程也称为真菌的群体感应系统。文中简要介绍真菌群体感应系统的研究进展,并讨论了真菌群体感应系统作为抗真菌感染靶点的可能性。     

Quorum sensing controls exopolysaccharide production in Sinorhizobium meliloti

Sinorhizobium meliloti is a soil bacterium capable of invading and establishing a symbiotic relationship with alfalfa plants. This invasion process requires the synthesis, by S. meliloti, of at least one of the two symbiotically important exopolysaccharides, succinoglycan and EPS II. We have previously shown that the sinRI locus of S. meliloti encodes a quorum-sensing system that plays a role in the symbiotic process. Here we show that the sinRI locus exerts one level of control through regulation of EPS II synthesis. Disruption of the autoinducer synthase gene, sinI, abolished EPS II production as well as the expression of several genes in the exp operon that are responsible for EPS II synthesis. This phenotype was complemented by the addition of acyl homoserine lactone (AHL) extracts from the wild-type strain but not from a sinI mutant, indicating that the sinRI-specified AHLs are required for exp gene expression. This was further confirmed by the observation that synthetic palmitoleyl homoserine lactone (C(16:1)-HL), one of the previously identified sinRI-specified AHLs, specifically restored exp gene expression. Most importantly, the absence of symbiotically active EPS II in a sinI mutant was confirmed in plant nodulation assays, emphasizing the role of quorum sensing in symbiosis.     

细菌中群体感应调节系统

细菌根据特定信号分子的浓度可以监测周围环境中自身或其它细菌的数量变化,当信号达到一定的浓度阈值时,能启动菌体中相关基因的表达来适应环境中的变化,这一调控系统被称为细菌的群体感应调节系统(QuorumSensing系统)。本文系统介绍了细菌感知种内与种间数量的群体感应调节系统,并阐述了植物针对病原菌这一信号系统的抗病策略。     

细菌密度感应系统抑制剂

许多条件致病菌依赖密度感应系统作为毒力表达的最重要的调节器。该文就革兰氏阴性细菌密度感应系统抑制剂的作用机制、分离与鉴定及应用等方面进行系统阐述。     

细菌群感效应的猝灭

细菌群感效应（quorum sensing,QS）是一种细菌种间和种内信息交流调控机制.研究证明,细菌群感效应与细菌生物膜的形成和某些人体、植物病原菌的发病机制有关,目前它已成为医学、生物工程、农业和环境工程等领域的研究热点,有望在此基础上开发出控制生物膜形成和病原菌致病性的新方法.该文介绍目前已有的细菌群感效应的抑制方法（即细菌群感猝灭,quorum quenching）,主要包括降低R蛋白活性、抑制信号分子合成,以及降解信号分子等.     

Quorum Sensing in Nitrogen-Fixing Rhizobia

Members of the rhizobia are distinguished for their ability to establish a nitrogen-fixing symbiosis with leguminous plants. While many details of this relationship remain a mystery, much effort has gone into elucidating the mechanisms governing bacterium-host recognition and the events leading to symbiosis. Several signal molecules, including plant-produced flavonoids and bacterially produced nodulation factors and exopolysaccharides, are known to function in the molecular conversation between the host and the symbiont. Work by several laboratories has shown that an additional mode of regulation, quorum sensing, intercedes in the signal exchange process and perhaps plays a major role in preparing and coordinating the nitrogen-fixing rhizobia during the establishment of the symbiosis. Rhizobium leguminosarum, for example, carries a multitiered quorum-sensing system that represents one of the most complex regulatory networks identified for this form of gene regulation. This review focuses on the recent stream of information regarding quorum sensing in the nitrogen-fixing rhizobia. Seminal work on the quorum-sensing systems of R. leguminosarum bv. viciae, R. etli, Rhizobium sp. strain NGR234, Sinorhizobium meliloti, and Bradyrhizobium japonicum is presented and discussed. The latest work shows that quorum sensing can be linked to various symbiotic phenomena including nodulation efficiency, symbiosome development, exopolysaccharide production, and nitrogen fixation, all of which are important for the establishment of a successful symbiosis. Many questions remain to be answered, but the knowledge obtained so far provides a firm foundation for future studies on the role of quorum-sensing mediated gene regulation in host-bacterium interactions.     

根瘤菌群体感应系统研究进展*

群体感应是指细菌中依赖于细胞密度的基因表达调控过程,参与这种调节的系统被称为群体感应系统。N-酰基高丝氨酸内酯是大多数革兰氏阴性细菌群体感应系统的信号分子。这种系统调节细菌各种生理学反应和某些特定功能。在根瘤菌与宿主豆科植物成功建立共生关系的过程中,起着重要作用。详细的综述了根瘤菌中已发现的群体感应系统,并阐述了这种系统的调节功能和对实际应用的指导意义。     

细菌的群体感应及与病原菌致病性的关系

微生物的群体感应(quorum sensing,QS)也称为自诱导,是微生物间通过小分子分泌物(自诱导物)在细胞与细胞之间扩散以感知群体密度,并通过自诱导物的浓度及其与转录因子的相互作用调控整个群体细胞中一系列目标基因表达的一种自我感知系统.不同的细菌类型,其QS系统也有一定的差异.根据信号分子的不同,一般可以将细菌的QS系统分为3类,即以AHL为信号分子的革兰氏阴性细菌、以寡肽类物质为信号分子的革兰氏阳性细菌和以哈氏弧菌为代表的兼具上述两种类型QS系统特征的第三类QS系统.综述革兰氏阴性细菌、革兰氏阳性细菌和哈氏弧菌的3种不同QS系统及其在病原菌致病性方面的研究进展.     

假单胞菌Quorum sensing调控体系

群体感应(Quorum sensing,QS)是近来受到广泛关注的一种细菌群体行为调控机制,通过感应一些信号分子如酰基高丝氨酸环内酯(acyl-homoserine lactone,AHL)来判断菌群密度和周围环境变化,假单胞菌中同样也有AHL信号分子,当信号达到一定的浓度阈值时,能启动菌体中相关基因的表达来适应环境中的变化,从而调节菌体的群体行为(如致病性及群体生长调节)。众多报道说明了假单胞菌的群体感应调节系统是由一些全面的调节子所调控的。本文系统介绍了假单胞菌群体感应调控系统,并分析假单胞菌在该系统中复杂的应答反应。     

Optimal Census by Quorum Sensing

Quorum sensing is the regulation of gene expression in response to changes in cell density. To measure their cell density, bacterial populations produce and detect diffusible molecules called autoinducers. Individual bacteria internally represent the external concentration of autoinducers via the level of monitor proteins. In turn, these monitor proteins typically regulate both their own production and the production of autoinducers, thereby establishing internal and external feedbacks. Here, we ask whether feedbacks can increase the information available to cells about their local density. We quantify available information as the mutual information between the abundance of a monitor protein and the local cell density for biologically relevant models of quorum sensing. Using variational methods, we demonstrate that feedbacks can increase information transmission, allowing bacteria to resolve up to two additional ranges of cell density when compared with bistable quorum-sensing systems. Our analysis is relevant to multi-agent systems that track an external driver implicitly via an endogenously generated signal.     

细菌群体感应的信号转导机制及其对抗生素生产的影响

摘要：细菌的群体感应是一种群体行为调控机制。自然界中的很多细菌都有这种能力,即分泌一种或多种信号分子,通过这些信号分子的浓度来感知菌群密度,调控一系列相应靶基因的表达。在这些受调控的基因中,备受关注的是信号分子对抗生素生产的调节。本文综述了群体感应机制的最新研究进展和它对抗生素生产的调节,尤其对洋葱伯克霍尔德菌(Burkholderia. cepacia)进行了较为详细的探讨。     

Implications of Rewiring Bacterial Quorum Sensing

Bacteria employ quorum sensing, a form of cell-cell communication, to sense changes in population density and regulate gene expression accordingly. This work investigated the rewiring of one quorum-sensing module, the lux circuit from the marine bacterium Vibrio fischeri. Steady-state experiments demonstrate that rewiring the network architecture of this module can yield graded, threshold, and bistable gene expression as predicted by a mathematical model. The experiments also show that the native lux operon is most consistent with a threshold, as opposed to a bistable, response. Each of the rewired networks yielded functional population sensors at biologically relevant conditions, suggesting that this operon is particularly robust. These findings (i) permit prediction of the behaviors of quorum-sensing operons in bacterial pathogens and (ii) facilitate forward engineering of synthetic gene circuits.     

Messing with Bacterial Quorum Sensing

Quorum sensing is widely recognized as an efficient mechanism to regulate expression of specific genes responsible for communal behavior in bacteria. Several bacterial phenotypes essential for the successful establishment of symbiotic, pathogenic, or commensal relationships with eukaryotic hosts, including motility, exopolysaccharide production, biofilm formation, and toxin production, are often regulated by quorum sensing. Interestingly, eukaryotes produce quorum-sensing-interfering (QSI) compounds that have a positive or negative influence on the bacterial signaling network. This eukaryotic interference could result in further fine-tuning of bacterial quorum sensing. Furthermore, recent work involving the synthesis of structural homologs to the various quorum-sensing signal molecules has resulted in the development of additional QSI compounds that could be used to control pathogenic bacteria. The creation of transgenic plants that express bacterial quorum-sensing genes is yet another strategy to interfere with bacterial behavior. Further investigation on the manipulation of quorum-sensing systems could provide us with powerful tools against harmful bacteria.     

The Symbiotic Biofilm of Sinorhizobium fredii SMH12, Necessary for Successful Colonization and Symbiosis of Glycine max cv Osumi,Is Regulated by Quorum Sensing Systems and Inducing Flavonoids via NodD1

Bacterial surface components, especially exopolysaccharides, in combination with bacterial Quorum Sensing signals are crucial for the formation of biofilms in most species studied so far. Biofilm formation allows soil bacteria to colonize their surrounding habitat and survive common environmental stresses such as desiccation and nutrient limitation. This mode of life is often essential for survival in bacteria of the genera Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Rhizobium. The role of biofilm formation in symbiosis has been investigated in detail for Sinorhizobium meliloti and Bradyrhizobium japonicum. However, for S. fredii this process has not been studied. In this work we have demonstrated that biofilm formation is crucial for an optimal root colonization and symbiosis between S. fredii SMH12 and Glycine max cv Osumi. In this bacterium, nod-gene inducing flavonoids and the NodD1 protein are required for the transition of the biofilm structure from monolayer to microcolony. Quorum Sensing systems are also required for the full development of both types of biofilms. In fact, both the nodD1 mutant and the lactonase strain (the lactonase enzyme prevents AHL accumulation) are defective in soybean root colonization. The impairment of the lactonase strain in its colonization ability leads to a decrease in the symbiotic parameters. Interestingly, NodD1 together with flavonoids activates certain quorum sensing systems implicit in the development of the symbiotic biofilm. Thus, S. fredii SMH12 by means of a unique key molecule, the flavonoid, efficiently forms biofilm, colonizes the legume roots and activates the synthesis of Nod factors, required for successfully symbiosis.     

Phenotypic Heterogeneity in Bacterial Quorum Sensing Systems

Quorum sensing is usually thought of as a collective behavior in which all members of a population partake. However, over the last decade, several reports of phenotypic heterogeneity in quorum sensing-related gene expression have been put forward, thus challenging this view. In the respective systems, cells of isogenic populations did not contribute equally to autoinducer production or target gene activation, and in some cases, the fraction of contributing cells was modulated by environmental factors. Here, we look into potential origins of these incidences and into how initial cell-to-cell variations might be amplified to establish distinct phenotypic heterogeneity. We furthermore discuss potential functions heterogeneity in bacterial quorum sensing systems could serve: as a preparation for environmental fluctuations (bet hedging), as a more cost-effective way of producing public goods (division of labor), as a loophole for genotypic cooperators when faced with non-contributing mutants (cheat protection), or simply as a means to fine-tune the output of the population as a whole (output modulation). We illustrate certain aspects of these recent developments with the model organisms Sinorhizobium meliloti, Sinorhizobium fredii and Bacillus subtilis, which possess quorum sensing systems of different complexity, but all show phenotypic heterogeneity therein.     

微生物群体效应信号分子研究进展

微生物细胞通过分泌可溶性小分子控制群体行为,获得生存优势的行为称为群体效应（Quorum sensing）。单细胞微生物利用群体效应获得多细胞生物的功能,从而提高自身在环境中的竞争力。信号分子是微生物发挥群体效应、进行信息交流的关键因子。信号分子普遍存在于各类微生物群体中,其结构、性质与功能存在巨大的种属差异,对信号分子进行全面的研究将有助于更加深入地了解和利用微生物群体效应。本文主要对群体效应信号分子在种类、结构、来源以及功能等方面的研究进展进行介绍。