群体猝灭技术在控制MBR生物污染中的研究进展

膜生物反应器(MBR)广泛用于处理市政污水,但膜污染仍是MBR的应用瓶颈。基于微生物群体感应(QS)理论的群体猝灭(QQ)技术是一种具有较好前景的膜污染控制方法。QQ技术可干扰微生物的QS系统,进而抑制胞外聚合物的分泌和生物膜的形成,从根本上达到控制MBR生物污染的目的。对利用QQ技术控制MBR生物污染的研究进展进行总结,提出该技术面临的挑战,并对今后采用QQ技术减缓膜污染的研究进行展望。     

应用群体感应淬灭技术控制MBR膜污染的研究进展

膜生物反应器(MBR)被广泛应用于污水的深度处理和回用。然而,膜表面的生物污染一直是MBR应用中的难题,至今仍未得到有效解决。研究结果表明,生物膜的形成与细胞间的群体感应(QS)有关,因此,通过干扰QS系统而阻止生物膜形成的群体淬灭(QQ)技术有望从根本上有效减缓MBR膜表面的生物污染。文中综述了微生物信号分子、QS机制以及各种控制MBR膜污染的QQ方法,为MBR膜生物污染控制技术的发展提供了相关信息。     

基于群体淬灭理论MBR减缓膜污染研究进展

膜生物反应器(membrane bioreactor,MBR)已成为一个十分有前景的废水处理工艺,该工艺具有出水水质好、占地面积小等优势.然而,由于微生物附着在膜表面而发生的生物污染现象,致使出水通量下降,限制了MBR的大规模推广应用.最近,一种新兴的、基于群体感应(quorum sensing,QS)的群体淬灭(quorum quenching,QQ)技术在延缓MBR膜污染领域的应用备受关注.QQ通过干扰群体感应系统而阻止其所依赖信号分子的基因表达,从而可有效抑制膜表面生物膜的形成.本文首先介绍了群体感应机理,并根据不同的群体淬灭物质,归纳总结了群体淬灭技术在延缓MBR膜污染的最新研究进展,最后对该领域的研究进行了展望.     

基于群体感应调控细菌生物膜形成研究进展

近些年来,许多研究都表明细菌等微生物之间存在群体感应现象(quorum sensing,QS).许多细菌都能合成并分泌自诱导物质来调控基因的表达调控生物膜的形成,以此保证细菌在生长过程中适应新的环境.生物膜(biofilm)的存在与细菌的抗逆能力有很大的关联,基于驱散群体感应抑制生物膜的形成也成了目前的研究热点之一.本...     

反渗透膜生物污染的研究进展

综述了近年来关于反渗透膜生物污染的研究进展。首先介绍了反渗透膜生物污染的机理,包括微生物与膜表面的吸附作用以及外界因素对微生物沉积的影响;然后阐述了如何监测和预警生物污染;并讨论了对生物污染的控制和预防方法,包括预处理、膜表面改性、膜清洗以及微生物群体感应抑制。     

MBR膜生物污染的生物控制方法研究进展

膜生物反应器(MBR)因其具有出水水质优质稳定、剩余污泥少、运行控制灵活等优点,被广泛应用于国内外水处理领域。然而,膜生物污染是制约MBR进一步发展的瓶颈问题,一些研究者已尝试多种方法控制膜的生物污染,但都有其各自的缺陷。其中,通过利用微生物自身代谢来控制膜生物污染的生物控制策略,正得到人们越来越多的关注。回顾了生物污染的形成过程,总结了传统物理化学控制方法的缺点,同时介绍了近年来国内外膜生物污染的生物控制方法研究进展,包括酶降解法、群体感应抑制法、能量解耦法、一氧化氮诱导法、噬菌体法和D-氨基酸法。最后根据目前国内外的研究现状,展望了生物控制方法未来的研究前景。     

反渗透膜生物污染的影响因素及控制方法的研究进展

由于人口的增长和淡水资源的短缺,各种水处理技术应运而生,其中RO技术作为一项新兴膜分离技术,在海水淡化、污水处理、再生水回用等方面都有着广泛的应用。但是膜污染问题的存在,成为膜技术在饮用水和污水处理中广泛应用的瓶颈。其中生物污染对膜的破坏性最为严重,其污染也最难控制。回顾了生物污染的形成过程,主要列举了影响生物膜初始形成的几种因素:菌体特性、膜表面特性、进水组分等。同时讨论了生物污染的控制和预防方法,包括预处理、RO膜表面改性和微生物群体感应抑制。最后根据目前国内外的研究现状,展望了生物污染未来的研究前景。     

基于群体感应相关菌群分析的HMBR膜污染控制研究

微生物群体感应现象已经在污水处理中被验证并应用于膜污染控制,但是其在复合式膜生物反应器（HMBR中的膜污染控制研究鲜有报道。构建了HMBR污水处理系统,并在不同污泥龄（SRT=10、20、30 d）下运行HMBR设备,通过分析出水水质考察HMBR污水处理系统对污染物的去除效能;采用高通量测序检测群体感应相关菌群的群落结构,并结合跨膜压差、信号分子浓度深入解析群体感应调控HMBR膜污染的机理。实验结果表明,HMBR在SRT=30 d的工况下出水水质最好,膜组件运行周期最长,为最佳工况;HMBR内检测到多种群体感应猝灭（QQ）菌,其中从单胞菌科（Comamonas）、黄单胞菌科（Xanthomonadacea）和厌氧绳菌科（Anaerolineaceae）相对丰度较大;在长SRT下QQ菌比群体感应（QS）菌相对丰度更具优势,有助于降低HMBR内部信号分子的浓度,阻碍EPS分泌过程的正常进行,从而优化膜组件运行周期,因此通过延长SRT来抑制群体感应强度是一种有效的HMBR膜污染调控手段。     

革兰氏阴性菌群体感应抑制剂的研究进展

群体感应是一种通过菌体密度来协同控制细菌特定基因表达的现象。由此产生的群体感应抑制剂在抑制细菌毒性基因表达时不会对细菌产生生长压力,从而避免了细菌耐药性的产生。这一新颖的抑菌机制使其在开发新型抗感染药物方面有很大潜力。研究中,简要描述了研究最广泛的革兰氏阴性菌群体感应系统、群体感应抑制剂的作用方法和来源类别。突出介绍了天然来源和化学合成两个方面的群体感应抑制剂,并且介绍了几种群体感应抑制剂的应用。     

影响反渗透膜生物污染的因素及控制方法

介绍了关于反渗透膜的生物污染影响因素,包括微生物自身特征,膜表面特征及操作条件等对生物污染薄膜生长的影响,叙述了反渗透膜生物污染的控制方法,提出了目前反渗透膜抗生物污染的三大防治手段所存在的问题。认为反渗透膜抗生物污染的研究依旧应以微生物在反渗透膜表面的形成过程及吸附机理为主,从而研发出更具有针对性的新型抗生物污染膜材料。     

AHL-QS减缓膜生物反应器膜污染研究进展

首先介绍N-乙酰高丝氨酸环内酯（N-acyl homoserine lactone,AHL）型生物群体感应（quorum sensing,QS）信号分子对膜生物反应器（membrane bioreactor,MBR）膜表面形成生物膜的调节机制,通过AHL-QS信号分子细胞间的交流,可决定生物膜形成及胞外聚合物（extracellular polymeric substances,EPS）分泌;系统阐述了应用AHL-QS信号分子降解酶及淬灭剂对MBR生物膜污染的控制效果,抑制或降解信号分子可显著降低生物膜形成能力,从根本上控制膜污染。此外,针对降解酶及淬灭剂新的固定化技术在MBR中的应用也作了介绍,如磁性载体、膜表面负载、微生物-管束及多孔微球包埋细胞技术。以AHL-QS为基础的膜污染控制策略对于MBR应用前景广阔,然而该技术的工程化研究仍有待进一步深入;加强AHL-QS信号分子识别及进一步明确QS系统对微生物代谢机制的影响是该领域未来重要的研究方向。     

Quorum Quenching Enzymes and Their Application in Degrading Signal Molecules to Block Quorum Sensing-Dependent Infection

With the emergence of antibiotic-resistant strains of bacteria, the available options for treating bacterial infections have become very limited, and the search for a novel general antibacterial therapy has received much greater attention. Quorum quenching can be used to control disease in a quorum sensing system by triggering the pathogenic phenotype. The interference with the quorum sensing system by the quorum quenching enzyme is a potential strategy for replacing traditional antibiotics because the quorum quenching strategy does not aim to kill the pathogen or limit cell growth but to shut down the expression of the pathogenic gene. Quorum quenching enzymes have been identified in quorum sensing and non-quorum sensing microbes, including lactonase, acylase, oxidoreductase and paraoxonase. Lactonase is widely conserved in a range of bacterial species and has variable substrate spectra. The existence of quorum quenching enzymes in the quorum sensing microbes can attenuate their quorum sensing, leading to blocking unnecessary gene expression and pathogenic phenotypes. In this review, we discuss the physiological function of quorum quenching enzymes in bacterial infection and elucidate the enzymatic protection in quorum sensing systems for host diseases and their application in resistance against microbial diseases.     

Structure-based discovery and experimental verification of novel AI-2 quorum sensing inhibitors against Vibrio harveyi

Quorum sensing has been implicated in the control of pathologically relevant bacterial behavior such as secretion of virulence factors, biofilm formation, sporulation, and swarming motility. The AI-2 quorum sensing pathway is found in both gram-positive and gram-negative bacteria. Therefore, antagonizing AI-2 quorum sensing is a possible approach to modifying bacterial behaviour. However, efforts in developing inhibitors of AI-2-mediated quorum sensing are especially lacking. High-throughput virtual screening using the V. harveyi LuxP crystal structure identified two compounds that were found to antagonize AI-2-mediated quorum sensing in V. harveyi without cytotoxicity. The sulfone functionality of these inhibitors was identified as critical to their ability to mimic the natural ligand in their interactions with Arg 215 and Arg 310 of the active site.     

Comparative analyses of N-acylated homoserine lactones reveal unique structural features that dictate their ability to activate or inhibit quorum sensing

Bacterial quorum sensing is mediated by low molecular-weight signals and plays a critical role in both the pathogenesis of infectious disease and beneficial symbioses. There is significant interest in the development of synthetic ligands that can intercept bacterial quorum sensing signals and modulate these outcomes. Here, we report the design and comparative analysis of the effects of approximately 90 synthetic N-acylated homoserine lactones (AHLs) on quorum sensing in three Gram negative bacterial species and a critical examination of the structural features of these ligands that dictate agonistic and antagonistic activity, and selectivity for different R protein targets. These studies have revealed the most comprehensive set of structure-activity relationships to date that direct AHL-mediated quorum sensing and a new set of chemical probes with which to study this complex signaling process. Furthermore, this work provides a foundation on which to design next-generation quorum sensing modulators with improved activities and selectivities.     

A Genetic Circuit System Based on Quorum Sensing Signaling for Directed Evolution of Quorum‐Quenching Enzymes

Quorum sensing is a cell–cell communication mechanism that is involved in the regulation of biological functions such as luminescence, virulence, and biofilm formation. Quorum‐quenching enzymes, which interrupt quorum‐sensing signaling through degradation of quorum‐sensing molecules, have emerged as a new approach to controlling and preventing bacterial virulence and pathogenesis. In an effort to develop quorum‐quenching enzymes with improved catalytic activities, a genetic circuit system based on acylhomoserine‐lactone (AHL)‐mediated quorum‐sensing signaling was constructed. The genetic circuit system was composed of lux‐R, lux‐I promoter, β‐lactamase, and β‐lactamase inhibitor, and designed to confer antibiotic resistance on host cells expressing an AHL‐degrading enzyme, thereby enabling rapid screening of quorum‐quenching enzymes. To demonstrate the utility of the genetic circuit system, we attempted the directed evolution of the AHL hydrolase from Bacillus sp. The genetic circuit system was shown to be effective in screening of quorum‐quenching enzymes with high catalytic efficiency. From these results it is expected that the genetic circuit system can be widely used for the isolation and directed evolution of quorum‐quenching enzymes with greater potential.     

Intra-Species Bacterial Quorum Sensing Studied at Single Cell Level in a Double Droplet Trapping System

In this paper, we investigated the intra-species bacterial quorum sensing at the single cell level using a double droplet trapping system. Escherichia coli transformed to express the quorum sensing receptor protein, LasR, were encapsulated in microdroplets that were positioned adjacent to microdroplets containing the autoinducer, N-(3-oxododecanoyl)- l-homoserine lactone (OdDHL). Functional activation of the LasR protein by diffusion of the OdDHL across the droplet interface was measured by monitoring the expression of green fluorescent protein (GFP) from a LasR-dependent promoter. A threshold concentration of OdDHL was found to induce production of quorum-sensing associated GFP by E. coli. Additionally, we demonstrated that LasR-dependent activation of GFP expression was also initiated when the adjacent droplets contained single E. coli transformed with the OdDHL synthase gene, LasI, representing a simple quorum sensing circuit between two droplets.     

The Structural Determinants Accounting for the Broad Substrate Specificity of the Quorum Quenching Lactonase GcL

Quorum quenching lactonases are enzymes capable of hydrolyzing lactones, including N-acyl homoserine lactones (AHLs). AHLs are molecules known as signals in bacterial communication dubbed quorum sensing. Bacterial signal disruption by lactonases was previously reported to inhibit behavior regulated by quorum sensing, such as the expression of virulence factors and the formation of biofilms. Herein, we report the enzymatic and structural characterization of a novel lactonase representative from the metallo-β-lactamase superfamily, dubbed GcL. GcL is a broad spectrum and highly proficient lactonase, with k_cat/K_M values in the range of 10⁴ to 10⁶ m ⁻¹ s⁻¹. Analysis of free GcL structures and in complex with AHL substrates of different acyl chain length, namely, C4-AHL and 3-oxo-C12-AHL, allowed their respective binding modes to be elucidated. Structures reveal three subsites in the binding crevice: 1) the small subsite where chemistry is performed on the lactone ring; 2) a hydrophobic ring that accommodates the amide group of AHLs and small acyl chains; and 3) the outer, hydrophilic subsite that extends to the protein surface. Unexpectedly, the absence of structural accommodation for long substrate acyl chains seems to relate to the broad substrate specificity of the enzyme.     

Quorum Sensing and Phytochemicals

Most infectious diseases are caused by bacteria, which proliferate within quorum sensing (QS)-mediated biofilms. Efforts to block QS in bacteria and disrupt biofilms have enabled the identification of bioactive molecules that are also produced by plants. This mini review primarily focuses on natural QS inhibitors, which display potential for treating bacterial infections and also enhance the safety of food supply.     

RpoN Regulates Virulence Factors of Pseudomonas aeruginosa via Modulating the PqsR Quorum Sensing Regulator

The alternative sigma factor RpoN regulates many cell functions, such as motility, quorum sensing, and virulence in the opportunistic pathogen Pseudomonas aeruginosa (P. aeruginosa). P. aeruginosa often evolves rpoN-negative variants during the chronic infection in cystic fibrosis patients. It is unclear how RpoN interacts with other regulatory mechanisms to control virulence of P. aeruginosa. In this study, we show that RpoN modulates the function of PqsR, a quorum sensing receptor regulating production of virulence factors including the phenazine pyocyanin. The ∆rpoN mutant is able to synthesize 4-quinolone signal molecule HHQ but unable to activate PqsR and Pseudomonas quinolone signal (pqs) quorum sensing. The ∆rpoN mutant produces minimal level of pyocyanin and is unable to produce the anti-staphylococcal agents. Providing pqsR in trans in the ∆rpoN mutant restores its pqs quorum sensing and virulence factor production to the wild-type level. Our study provides evidence that RpoN has a regulatory effect on P. aeruginosa virulence through modulating the function of the PqsR quorum sensing regulator.     

A Nitric Oxide-Responsive Quorum Sensing Circuit in Vibrio harveyi Regulates Flagella Production and Biofilm Formation

Cell signaling plays an important role in the survival of bacterial colonies. They use small molecules to coordinate gene expression in a cell density dependent manner. This process, known as quorum sensing, helps bacteria regulate diverse functions such as bioluminescence, biofilm formation and virulence. In Vibrio harveyi, a bioluminescent marine bacterium, four parallel quorum-sensing systems have been identified to regulate light production. We have previously reported that nitric oxide (NO), through the H-NOX/HqsK quorum sensing pathway contributes to light production in V. harveyi through the LuxU/LuxO/LuxR quorum sensing pathway. In this study, we show that nitric oxide (NO) also regulates flagellar production and enhances biofilm formation. Our data suggest that V. harveyi is capable of switching between lifestyles to be able to adapt to changes in the environment.