Three-Dimensional Numerical Simulations of Biofilm Dynamics with Quorum Sensing in a Flow Cell

We develop a multiphasic hydrodynamic theory for biofilms taking into account interactions among various bacterial phenotypes, extracellular polymeric substance (EPS), quorum sensing (QS) molecules, solvent, and antibiotics. In the model, bacteria are classified into down-regulated QS, up-regulated QS, and non-QS cells based on their QS ability. The model is first benchmarked against an experiment yielding an excellent fit to experimental measurements on the concentration of QS molecules and the cell density during biofilm development. It is then applied to study development of heterogeneous structures in biofilms due to interactions of QS regulation, hydrodynamics, and antimicrobial treatment. Our 3D numerical simulations have confirmed that (i). QS is beneficial for biofilm development in a long run by building a robust EPS population to protect the biofilm; (ii). biofilms located upstream can induce QS downstream when the colonies are close enough spatially; (iii). QS induction may not be fully operational and can even be compromised in strong laminar flows; (v). the hydrodynamic stress alters the biofilm morphology. Through further numerical investigations, our model suggests that (i). QS-regulated EPS production contributes to the structural formation of heterogeneous biofilms; (ii) QS down-regulated cells tend to grow at the surface of the biofilm while QS up-regulated ones tend to grow in the bulk; (iii) when nutrient supply is sufficient, QS induction might be more effective upstream than downstream; (iv) QS may be of little benefit in a short timescale in term of fighting against invading strain/species; (v) the material properties of biomass (bacteria and EPS) have strong impact on the dilution of QS molecules under strong shear flow. In addition, with this modeling framework, hydrodynamic details and rheological quantities associated with biofilm formation under QS regulation can be resolved.     

群体感应及其在动物病原菌致病中的作用

摘要: 群体感应是指微生物群体某些基因的表达受到与群体密度相关的信号分子调控的现象。微生物以酰基高丝氨酸内酯化合物,某些短肽分子,呋喃酮类化合物,以及一些小分子物质为信号分子,介导不同的群体感应系统。各群体感应系统之间以平行协同或层次串连的方式组织起来调控微生物各种基因。众多病原菌致病基因的表达与群体感应密切相关,主要表现在：群体感应帮助微生物对宿主的侵袭和定殖;调控毒力因子的产生和作用于宿主;以及介导病原菌对宿主的免疫能力和药物抗性。进行群体感应对微生物致病过程调控的研究,将有利于从群体感应入手进行病原菌防控新策略的探索。     

Quorum sensing has an unexpected role in virulence in the model pathogen Citrobacter rodentium

The bacterial mouse pathogen Citrobacter rodentium causes attaching and effacing (AE) lesions in the same manner as pathogenic Escherichia coli, and is an important model for this mode of pathogenesis. Quorum sensing (QS) involves chemical signalling by bacteria to regulate gene expression in response to cell density. E. coli has never been reported to have N-acylhomoserine lactone (AHL) QS, but it does utilize luxS-dependent signalling. We found production of AHL QS signalling molecules by an AE pathogen, C. rodentium. AHL QS is directed by the croIR locus and a croI mutant is affected in its surface attachment, although not in Type III secretion. AHL QS has an important role in virulence in the mouse as, unexpectedly, the QS mutant is hypervirulent; by contrast, we detected no impact of luxS inactivation. Further study of QS in Citrobacter should provide new insights into AE pathogenesis. As the croIR locus might have been horizontally acquired, AHL QS might exist in some strains of pathogenic E. coli.     

植物对细菌群体感应系统的反应

细菌的群体感应系统参与包括动植物病原细菌致病因子产生在内的许多生物学功能的调节。植物可以感知细菌群体感应系统及其信号分子,并作出复杂反应。植物可能受细菌群体感应信号分子诱导产生系统性防御反应,能够分泌细菌群体感应信号分子的类似物,可能产生降解细菌N-酰基高丝氨酸内酯信号分子的酶来阻断或干扰细菌群体感应系统。     

Anti-activator QslA defines the quorum sensing threshold and response in Pseudomonas aeruginosa

Quorum sensing (QS) in a bacterial population is activated when extracellular concentration of QS signal reaches a threshold, but how this threshold is determined remains largely unknown. In this study, we report the identification and characterization of a novel anti-activator encoded by qslA in Pseudomonas aeruginosa. The null mutation of qslA elevated AHL-dependent QS and PQS signalling, increased the expression of QS-dependent genes, and enhanced the virulence factor production and pathogenicity. We further present evidence that modulation of QS by QslA is due to protein-protein interaction with LasR, which prevents LasR from binding to its target promoter. QslA also influences the threshold concentration of QS signal needed for QS activation; in the absence of qslA, QS is activated by nine times less N-3-oxo-dodecanoyl-homoserine lactone (3-oxo-C12-HSL) than that in wild type. The findings from this study depict a new mechanism that governs the QS threshold in P. aeruginosa.     

细菌群体感应信号分子的光电检测技术

群体感应（quorum sensing，QS）是一种依赖菌群密度的细菌交流系统。在探究细菌群体感应系统的调控机制中，对QS信号分子的鉴别和检测是不可或缺的环节，其对生命科学、药学等领域涉及细菌等微生物的相互作用、高效检测和作用机制解析等具有重要的参考意义。本文在总结不同类型细菌QS信号分子来源和结构的基础上，对QS信号分子的光电检测方法和技术进行了综述，重点对光电传感检测的敏感介质、传感界面、传感机制及测试效果进行探讨，同时关注了将微流控芯片分析技术应用于细菌QS信号分子原位监测的相关研究进展。     

The presence, type and role of N-acyl homoserine lactone quorum sensing in fluorescent Pseudomonas originally isolated from rice rhizospheres are unpredictable

In Gram-negative bacteria, a typical quorum-sensing (QS) system involves the production and response to N-acyl homoserine lactones (AHLs). It still remains unclear as to how pivotal and conserved AHL QS is in root-colonizing rhizosphere Pseudomonas. We, therefore, performed a systematic study of AHL QS on a set of 50 rice rhizosphere Pseudomonas isolates. We also isolated the AHL QS genes in two representative strains and analyzed the role of AHL QS regulation of various phenotypes. Our results are discussed with the current knowledge of AHL QS of rhizosphere Pseudomonas, implicating a lack of conservation and an unpredictable role played by AHL QS in this group of bacteria.     

Quorum sensing in the context of food microbiology

Food spoilage may be defined as a process that renders a product undesirable or unacceptable for consumption and is the outcome of the biochemical activity of a microbial community that eventually dominates according to the prevailing ecological determinants. Although limited information are reported, this activity has been attributed to quorum sensing (QS). Consequently, the potential role of cell-to-cell communication in food spoilage and food safety should be more extensively elucidated. Such information would be helpful in designing approaches for manipulating these communication systems, thereby reducing or preventing, for instance, spoilage reactions or even controlling the expression of virulence factors. Due to the many reports in the literature on the fundamental features of QS, e.g., chemistry and definitions of QS compounds, in this minireview, we only allude to the types and chemistry of QS signaling molecules per se and to the (bioassay-based) methods of their detection and quantification, avoiding extensive documentation. Conversely, we attempt to provide insights into (i) the role of QS in food spoilage, (ii) the factors that may quench the activity of QS in foods and review the potential QS inhibitors that might "mislead" the bacterial coordination of spoilage activities and thus may be used as biopreservatives, and (iii) the future experimental approaches that need to be undertaken in order to explore the "gray" or "black" areas of QS, increase our understanding of how QS affects microbial behavior in foods, and assist in finding answers as to how we can exploit QS for the benefit of food preservation and food safety.     

QT/QS2 index in patients with arterial hypertension, mitral valve prolapse and hyperthyroidism]

QT/QS2 ratio has been assessed in 26 patients with both borderline and mild hypertension and mitral valve prolapse syndrome (19 patients), and hyperthyroidism (16 patients) in comparison with method control groups. The following polycardiographic parameters have been analyzed: QT, QTp, QS2, QT/QS2, and QTp/QS2. Higher values of QT/QS2 ratio have been noted in patients with mitral valve prolapse syndrome and hyperthyroidism than that in the control group. There has been no difference in patients with mild hypertension while the values of the analyzed parameter have been significantly lower in patients with borderline hypertension. QT has been longer than QS2 (QT)QS2 1/in 9 (56%) patients with hyperthyroidism. A positive correlation between QT/QS2 ratio and ++thyroxine levels have been noted in these patients. QT values have been higher than QS2 values only in 1 patient with mild hypertension. It seems that QT/QS2 value has limited value as an indirect index of the adrenergic activity in the dysfunction of the autonomic nervous system.     

Multiple roles of TorD-like chaperones in the biogenesis of molybdoenzymes

Studies on cultured cells and in infection models have shown that cell density-dependent quorum-sensing (QS) controls many of the known virulence factors of Pseudomonas aeruginosa . However, it is less clear what role QS plays in chronic human lung infections associated with cystic fibrosis (CF). The involvement of QS in biofilm development, crucial to the establishment of long-term infections, suggests a role in the early stages of infection. However, the accumulation of QS mutants during chronic CF infections has been taken to indicate that any role diminishes thereafter. Here, we discuss the evidence for a continuing role for QS in P. aeruginosa CF infections, including QS activity in CF sputa and CF-relevant effects of QS-regulated products, such as pyocyanin. Bacterial population behaviour in CF is complex, and the exact roles of QS remains unclear. Therapeutic strategies directed against QS suggest that a greater understanding of bacterial populations during infection would be a valuable research goal from a clinical perspective.     

产Ⅱ类细菌素乳酸菌群体感应及其应用

群体感应(quorum sensing,QS)是微生物通过感知与细胞密度相关的信号分子的浓度来调控基因表达的一种行为。许多产Ⅱ类细菌素乳酸菌通过自诱导肽介导的QS系统调控其细菌素的合成。本文综述了乳酸菌Ⅱ类细菌素合成的QS调控现象、调控机制、QS系统组分以及QS的应用。产Ⅱ类细菌素乳酸菌QS的研究,必将为揭示发酵调控机理、调控发酵过程提供新的研究平台,为食品级基因表达系统的开发提供新的选择。     

Kin selection, quorum sensing and virulence in pathogenic bacteria

Bacterial growth and virulence often depends upon the cooperative release of extracellular factors excreted in response to quorum sensing (QS). We carried out an in vivo selection experiment in mice to examine how QS evolves in response to variation in relatedness (strain diversity), and the consequences for virulence. We started our experiment with two bacterial strains: a wild-type that both produces and responds to QS signal molecules, and a lasR (signal-blind) mutant that does not release extracellular factors in response to signal. We found that: (i) QS leads to greater growth within hosts; (ii) high relatedness favours the QS wild-type; and (iii) low relatedness favours the lasR mutant. Relatedness matters in our experiment because, at relatively low relatedness, the lasR mutant is able to exploit the extracellular factors produced by the cells that respond to QS, and hence increase in frequency. Furthermore, our results suggest that because a higher relatedness favours cooperative QS, and hence leads to higher growth, this will also lead to a higher virulence, giving a relationship between relatedness and virulence that is in the opposite direction to that usually predicted by virulence theory.     

Quorum-sensing regulation of gene expression: Fundamental and applied aspects and the role in bacterial communication

Quorum sensing (QS) is a specific type of regulation of gene expression in bacteria; it is dependent on the population density. QS systems include two obligate components: a low-molecular-weight regulator (autoinducer), readily diffusible through the cytoplasmic membrane, and a regulatory receptor protein, which interacts with the regulator. As the bacterial population reaches a critical level of density, autoinducers accumulate to a necessary threshold value and abrupt activation (induction) of certain genes and operons occurs. By means of low-molecular-weight regulators, bacteria accomplish communication between cells belonging to the same or different species, genera, and even families. QS systems have been shown to play a key role in the regulation of various metabolic processes in bacteria and to function as global regulators of the expression of bacterial genes. Data are presented on different types of QS systems present in bacteria of various taxonomic groups, on the species specificity of these systems, and on communication of bacteria by means of QS systems. The possibility is considered of using QS regulation systems as targets while combating bacterial infections; other applied aspects of QS investigation are discussed.     

Quorum-sensing regulation of gene expression: fundamental and applied aspects and the role in bacterial communication

Quorum sensing (QS) is a specific type of regulation of gene expression in bacteria; it is dependent on the population density. QS systems include two obligate components: a low-molecular-weight regulator (autoinducer), readily diffusible through the cytoplasmic membrane, and a regulatory receptor protein, which interacts with the regulator. As the bacterial population reaches a critical level of density, autoinducers accumulate to a necessary threshold value and abrupt activation (induction) of certain genes and operons occurs. By means of low-molecular-weight regulators, bacteria accomplish communication between cells belonging to the same or different species, genera, and even families. QS systems have been shown to play a key role in the regulation of various metabolic processes in bacteria and to function as global regulators of the expression of bacterial genes. Data are presented on different types of QS systems present in bacteria of various taxonomic groups, on the species specificity of these systems, and on communication of bacteria by means of QS systems. The possibility is considered of using QS regulation systems as targets while combating bacterial infections; other applied aspects of QS investigation are discussed.     

霍乱弧菌群体感应系统影响生物膜形成的研究进展

群体感应(quorum sensing,QS)是指细胞感知周围同类细胞的多寡或密度并调控基因表达的系统,它对大多数细菌的生物膜形成至关重要。目前对霍乱弧菌的QS系统已有较深入的研究,该菌的群体感应系统通过HapR、LuxO等多种信号分子调控生物膜的形成及消散。干扰QS系统将成为治疗生物膜相关感染的新方向。     

An EAL domain protein and cyclic AMP contribute to the interaction between the two quorum sensing systems in Escherichia coli

Quorum sensing (QS) is a bacterial cell-cell communication process by which bacteria communicate using extracellular signals called autoinducers. Two QS systems have been identified in Escherichia coli K-12, including an intact QS system 2 that is stimulated by the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex and a partial QS system 1 that consists of SdiA (suppressor of cell division inhibitor) responding to signals generated by other microbial species. The relationship between QS system 1 and system 2 in E. coli, however, remains obscure. Here, we show that an EAL domain protein, encoded by ydiV, and cAMP are involved in the interaction between the two QS systems in E. coli. Expression of sdiA and ydiV is inhibited by glucose. SdiA binds to the ydiV promoter region in a dose-dependent, but nonspecific, manner; extracellular autoinducer 1 from other species stimulates ydiV expression in an sdiA-dependent manner. Furthermore, we discovered that the double sdiA-ydiV mutation, but not the single mutation, causes a 2-fold decrease in intracellular cAMP concentration that leads to the inhibition of QS system 2. These results indicate that signaling pathways that respond to important environmental cues, such as autoinducers and glucose, are linked together for their control in E. coli.     

Disruption of Cell-to-Cell Signaling Does Not Abolish the Antagonism of Phaeobacter gallaeciensis toward the Fish Pathogen Vibrio anguillarum in Algal Systems

Quorum sensing (QS) regulates Phaeobacter gallaeciensis antagonism in broth systems; however, we demonstrate here that QS is not important for antagonism in algal cultures. QS mutants reduced Vibrio anguillarum to the same extent as the wild type. Consequently, a combination of probiotic Phaeobacter and QS inhibitors is a feasible strategy for aquaculture disease control.     

Degradation of quillaja saponins by mixed culture of rumen microbes

Quillaja saponin (QS) was incubated at 39°C in an in vitro medium containing rumenliquor from a cow fed a roughage diet. Nodegradation of QS was observed up to 6 h offermentation. Incubation for 9, 12 and 24 hdecreased the content of QS by 16%, 45% and 100%.The content of QS did not decreasewhen incubated for 24 h in the medium containing autoclavedrumen liquor, suggestingthat rumen microbes have enzyme(s) capable of degrading QS. The fateof QSwill help gain a better understanding of mechanisms of action of QS on rumenfermentation,and its beneficial effects mediated by binding to ammonia.     

Development and comparison of whole-cell assay systems for quorum-sensing inhibitors based on TraR, LasR, and QscR

Quorum sensing (QS) is a cell density-dependent signaling system that is used by bacteria to coordinate gene expression within their population. In this study, the authors describe the development and characterization of various cell-based bioassay systems for detecting QS inhibitors based on three LuxR family proteins, TraR, LasR, and the recently identified QscR. Three different gram-negative bacteria, Escherichia coli, Agrobacterium tumefaciens, and Pseudomonas aeruginosa, were employed as reporter strains to overproduce one of the aforementioned QS activator proteins and respond to inhibitors. The nine different whole-cell assay systems (three reporter strains × three QS proteins) were evaluated for their applicability and reliability by studying quantitative responses to various furanones, which are potent inhibitors of the LuxR family proteins. These results demonstrate that the cell-based bioassay systems are sensitive and reliable tools for screening of QS activators and inhibitors. This study also suggests that furanones are potentially important QS inhibitors for many LuxR-type activator proteins.