革兰阳性细菌AIP型群体感应抑制剂的研究进展

以自诱导肽(autoinducter peptide)AIP为信号分子的细菌群体感应(quorum sensing,QS)系统存在于多种革兰阳性细菌中,是研究新型抗金黄色葡萄球菌等革兰阳性细菌药物的重要突破口。目前发现的AIP型群体感应抑制剂(quorum sensing inhibitors,QSIs)有小分子与大分子2种类型,笔者对这2类AIP型QSIs的研究进展进行综述,为新型抗菌药物的研发提供理论依据。     

芽孢杆菌R1共培养对嗜水气单胞菌NJ-1毒力基因表达的影响

为探讨芽孢杆菌潜在的淬灭靶点,本研究通过芽孢杆菌R1与嗜水气单胞菌NJ-1共培养,并对NJ-1生物量、信号分子产生量、毒力因子基因和群体感应(QS)关键调控基因表达量进行检测。结果显示:1NJ-1单独培养时,信号分子BHL和HHL的产量与NJ-1生长趋势一致,在27 h时达到峰值并启动Lux R表达,进而调控毒力因子金属蛋白酶、丝氨酸蛋白酶、肠毒素、气溶素和血溶素等表达,其在27~30 h时呈现峰值表达,通路Qse B在27~30 h启动表达,48 h时达到峰值,而种间调控Lux S基因表达一直处于低水平状态;2与芽孢杆菌R1共培养时,仅痕量AHLs信号分子被检出,毒力因子相关基因表达量均显著下调;Lux R表达受抑制,Lux S在36 h时表达量显著上调,未影响Qse B正常表达;3AHLs与R1共培养可被显著降解。研究表明,芽孢杆菌R1抑制NJ-1毒力因子相关基因表达可能与其对NJ-1多QS系统进行调控相关联。     

Motility-mediated regulation of virulence in Pseudomonas syringae

We have investigated Pseudomonas syringae pv. tabaci–plant interactions using a large variety of virulence-related mutants. A flagellin-defective mutant, ΔfliC, lost flagellar motility and the ability to produce N-acyl homoserine lactones; it had reduced ability to cause disease symptoms, but the expression of genes encoding a multidrug efflux pump transporter, mexEFoprN, was activated. A type IV pili (T4P)-defective mutant, ΔpilA, lost swarming motility, had reduced expression of hrp-related genes and virulence toward the host tobacco plant, but expression of the genes encoding another multidrug efflux pump transporter, mexABoprM, was activated. These results suggest that the genes regulating flagella- and T4P-mediated motilities also regulate expression of other virulence-related genes.     

自体诱导物合成酶基因的筛选及其功能分析

细菌在高细胞密度下通过产生一类化学信号分子(autoinducer,自体诱导物)感知细胞群体密度变化,从而对基因表达进行调控,这一现象被称为群体感应(quorum sensing).以中慢生型华癸根瘤菌 Mesorhizobium huakuii AS9 为出发菌株,利用转座子随机突变的方法获得了自体诱导物缺失突变株 YQ1,并克隆得到了其自体诱导物合成酶基因,命名为 mrhI;构建PmrhI-lacZ 转录融合表达质粒 pYQ1,通过同源重组的方法得到在华癸根瘤菌中 mrhI-lacZ 融合表达而且 mrhI 基因突变菌株YQ3.突变株 YQ3 的培养液上清不含有自体诱导物分子,通过 lacZ 报告基因的表达发现 mrhI 的表达受自体诱导物的调控,说明 mrhI 基因是 M. huakuii AS9 的群体感应体系中的自体诱导物合成酶基因.     

外源AHL对中慢生型天山根瘤菌群体感应系统作用的初步研究

通过将天山根瘤菌中的自体诱导物合成酶基因mrtI在转录水平融合肠lacZ构建了5'mrtI-lacZ融合表达菌株HMZ1.利用多株不同属的根瘤菌上清液对该菌株进行诱导,发现有3株豌豆根瘤菌和1株三叶草根瘤菌上清提取物能诱导mrtI基因的表达,且外源上清量越多,mrtI被诱导的程度越高,TLC的结果则显示它们可能有着相同的AI.该结果显示在相同功能的细菌间存在信号交流,为进一步研究群体感应调节在共生固氮上的作用提供了理论及实践依据.     

Dietary phytochemicals as quorum sensing inhibitors

Quorum sensing (QS) is a cell density dependent expression of species in bacteria mediated by hormone like compounds called autoinducers (AI). Several processes responsible for successful establishment of bacterial infection are mediated by QS. Inhibition of QS is therefore being considered as a new target for antimicrobial chemotherapy. Dietary phytochemicals are secondary metabolites in plants known to have several health benefits including antimicrobial activity. However, their ability to inhibit QS has never been studied. Our objective was to investigate the effect of sub-lethal concentrations (SLC) of bioactive dietary phytochemical extracts from common dietary fruit, herb and spice extracts on modulating QS mediated by AI in model bioassay test systems. QS inhibition was measured in violacein pigment producing Chromobacterium violaceum O26 (CVO26) and CV 31532 system, mediated by AI known as acylated homeserine lactone (AHL). We also investigated the effect of the sub-lethal concentrations of the extracts on swarming motility of pathogens Escherichia coli (EC)O157:H7 and Pseudomonas aeruginosa (PA-01). Our results indicate that all extracts significantly inhibited quorum sensing. The mechanism of inhibition appeared to be combination of interfering with AHL activity and modulating the synthesis of AHL's. Our results also indicated that various phytochemical extracts which inhibited QS also inhibited swarming of pathogenic bacteria, known to be modulated by QS. The observation that phytochemicals from foods can inhibit QS related processes opens up an exciting new strategy for antimicrobial chemotherapy and lead to the discovery of new category of antibiotics which can overcome the issues related to antimicrobial resistance.     

Disruption of bacterial quorum sensing: an unexplored strategy to fight infections in aquaculture

Disease outbreaks—some of them caused by pathogenic bacteria—are considered to be one of the largest constraints to development of the aquaculture sector. So far, antibiotics and disinfectants have only had limited success in the prevention or cure of aquatic disease. Moreover, the frequent use of biocides, especially in subtherapeutic doses, is leading to the rapid development of resistance. Therefore, there is an urgent need to develop alternative ways to control infections caused by bacterial pathogens in aquaculture. Many of these pathogens are found to control virulence factor expression by a cell-to-cell communication system. Hence, disruption of bacterial quorum sensing has been proposed as a new anti-infective strategy and several techniques that could be used to disrupt quorum sensing have been investigated. These techniques comprise (1) the inhibition of signal molecule biosynthesis, (2) the application of quorum sensing antagonists (including natural occurring as well as synthetic halogenated furanones, antagonistic quorum sensing molecules and undefined exudates of higher plants and algae), (3) the chemical inactivation of quorum sensing signals by oxidised halogen antimicrobials, (4) signal molecule biodegradation by bacterial lactonases and by bacterial and eukaryotic acylases and (5) the application of quorum sensing agonists. The few reports that deal with disruption of quorum sensing of aquatic pathogens, together with the results obtained with human and plant pathogens, indicate that this new approach has potential in fighting infections in aquaculture. However, before this new strategy can be applied in aquaculture, the impact of quorum sensing disruption on the virulence of aquatic pathogens and the impact of the proposed quorum sensing disrupting techniques on the aquaculture system of interest should be studied in more depth.     

糖类碳源对中慢生华癸根瘤菌群体感应基因mrhI/R表达的影响

克隆了中慢生华癸根瘤菌(Mesorhizobium huakuii)的mrh I和mrh R群体感应基因的启动子区域,至Lac Z翻译融合表达质粒载体p RA302中,经β-半乳糖苷酶活性检测发现,mrh I和mrh R的表达均受mrh I基因产物(自体诱导物)的正向调控。两种PTS糖类:葡萄糖和果糖的外源添加可以显著增加细菌的生长量,但却都同时抑制了mrh I和mrh R基因的表达,暗示在中慢生华癸根瘤菌中群体感应基因的表达可能受细菌中普遍存在的碳源代谢物阻遏现象的调节。     

Soil mineralization: An emergent process?

This paper argues that soil mineralization should be seen as an emergent process. While it is effecting mineralization the soil population shows many of the characteristics of recognised emergent systems such as ant colonies and slime moulds. In particular, the whole is more than the sum of the parts, and the system shows clear evidence of bottom-up organization. Furthermore, the ‘quorum sensing’ recently discovered in soil and other bacteria strongly suggests that chemical signalling plays a part among the soil population, as it does in other biological emergent systems. Emergent behaviour has consequences for measuring and modelling mineralization. The idea that the whole is more than the sum of the parts suggests that measurements must be made at a scale that includes all the parts, while the bottom-up organization implies that there is no controlling parameter on which a model can be centred. Other emergent systems have been simulated using simple sets of rules for organisms that correspond to the local information they use in practice, and this approach could be tried with mineralization. Candidate rules are suggested.