铜绿假单胞菌群体感应系统研究进展

群体感应系统是一种细胞密度依赖的基因表达系统,其广泛存在于细菌性病原体中,是细菌细胞通讯方式的一种。群体感应系统可利用细菌释放的信号分子不断监控周围细菌的密度。当细菌密度达到阈值时,群体感应系统网络将启动,参与调控生物被膜、细菌毒力等特定基因的表达,从而使临床抗感染治疗失败。而通过抑制群体感应系统,可一定程度上治疗铜绿假单胞菌引起的感染。本文通过查阅近年国内外相关文献,对铜绿假单胞菌群体感应系统研究进展进行总结,为临床铜绿假单胞菌治疗提供新的方向,即群体感应系统抑制剂有可能成为治疗铜绿假单胞菌感染的新策略。     

The epizoic diatom community on four bryozoan species from Helgoland (German Bight, North Sea)

The composition of the diatom community on the bryozoans Electra pilosa, Membranipora membranacea, Flustra foliacea, and Alcyonidium gelatinosum from the German Bight was studied by light and scanning electron microscopy. In total, members of 26 diatom genera were found, with Cocconeis, Tabularia, Licmophora, Amphora, and Navicula being the most abundant. The amount and the composition of the diatom covering seem to be typical for single bryozoan species. Electra pilosa and Membranipora membranacea showed a rather dense covering with 71–547 cells/mm² and 77–110 cells/mm², respectively. The most prominent genus on Electra pilosa was Cocconeis, reaching up to 58% of all diatoms in one sample, followed by Navicula, Tabularia and Amphora. The most abundant genera on Membranipora membranacea were Tabularia and Licmophora, making up almost 70% of all diatoms in one sample, followed by Navicula, Cocconeis and Amphora. The diatom composition was very stable on all Electra samples, but varied on Membranipora samples. With <1–27 cells/mm², diatoms were much less abundant on Alcyonidium gelatinosum. Members of the genera Tabularia and Navicula were the most frequently found benthic diatoms, whereas the planktonic forms Coscinodiscus, Cyclotella, and Thalassiosira made up 35% of the diatoms. On Flustra foliacea, diatoms were virtually absent, with fewer than 5 cells/mm². The low diatom numbers are probably due to toxic metabolites produced by the host. The same may be true for Alcyonidium gelatinosum, but here they might also be a consequence of the surface properties of the bryozoan. Electronic Publication     

Design,synthesis and biological evaluation of novel hamamelitannin analogues as potentiators for vancomycin in the treatment of biofilm related Staphylococcus aureus infections

Staphylococcus aureus is a frequent cause of biofilm-related infections. Bacterial cells within a biofilm are protected from attack by the immune system and conventional antibiotics often fail to penetrate the biofilm matrix. The discovery of hamamelitannin as a potentiator for antibiotics, recently led to the design of a more drug-like lead. In the present study, we want to gain further insight into the structure–activity relationship (S.A.R.) of the 5-position of the molecule, by preparing a library of 21 hamamelitannin analogues.     

群体感应信号分子及其抑制剂快速检测方法的建立

细菌能自发产生、释放一些特定的信号分子,并能感知其浓度变化,调节微生物的群体行为,这一调控系统称为群体感应。细菌群体感应参与包括人类、动植物病原菌致病力在内的多种生物学功能的调节,群体感应抑制剂成为抗感染药物开发的靶点。利用紫色色杆菌(Chromobacterium violaceum)和根癌农杆菌(Agrobacterium tumefaciens)作为指示菌,建立检测高丝氨酸内酯(AHLs)及其抑制剂的简便方法。结果表明,通过平板交叉划线接种,使用指示菌能够有效地检测AHLs,并且通过薄层层析(TLC)与细菌生物感应器相结合的方法可以快速、方便地鉴定AHLs的种类;通过双层平板法观察指示菌色素产生情况,能够有效地检测群体感应信号分子AHLs抑制剂,且该方法简单易行。     

The world within: Quantifying the determinants and outcomes of a host's microbiome

The fungal, bacterial, and viral microbial communities embedded as endosymbionts within all free-living organisms are extremely diverse and encode the vast majority of genes in the biosphere. Microbes in a human, for example, account for 100 times more genes than their host; similar results are emerging for virtually all free-living organisms. Disease is the best studied host–microbe interaction, but endosymbiotic microbial populations and communities also are responsible for critical functions in their hosts including nutrient uptake (plants), reduction in inflammatory responses (animals), digestion (animals), anti-herbivore defenses (plants), and pathogen resistance. In spite of the tremendous diversity and functional importance of the microbial biome to free-living organisms, we have little predictive understanding of the biotic and abiotic factors controlling within-host microbial community composition or the spatial scales at which anthropogenic changes affect host and microbial community interactions and functions. Current research suggests that anthropogenic changes to nutrient supply and food web composition can affect biological systems at scales ranging from individuals to continents. However, while current studies are clarifying the effects of some of these drivers on the structure and functioning of ecosystems, we have far less knowledge of their effects on microbial communities residing within hosts. Given the accelerating progress in metagenome studies, we are poised to make rapid advances in understanding the determinants and effects of within-host microbial communities.     

Isolation and identification of quorum quenching bacteria from environmental samples

A large number of Gram-negative pathogens produce N-acylhomoserine lactones (AHLs) as signal molecules for quorum sensing (QS). This cell-cell communication system allows them to coordinate gene expression and regulate virulence. Therefore, strategies to inhibit QS are promising for the control of infectious diseases. The aim of the present study was to develop a high-throughput method for the isolation and identification of AHL-degrading bacteria from environmental samples. Samples were cultured in a microtitre plate in a minimal medium containing 1 mM N-(3-oxo-dodecanoyl)-l-homoserine lactone and 2 mM N-(3-oxo-hexanoyl)-l-homoserine lactone as the sole sources of carbon and nitrogen. Isolates growing on this minimal medium were subcultured and identified by partial 16S rRNA gene sequencing. Subsequently, the AHL-degrading capacity of each isolate was evaluated in the Pseudomonas aeruginosa QSIS2 biosensor assay, as such or after treatment with heat or proteinase K. The 16 samples tested yielded a total of 59 isolates which are, either alone or as part of a consortium, able to use AHL signal molecules as sole sources of carbon and nitrogen. Follow-up experiments have shown that in each sample there is at least one isolate with quorum quenching (QQ) activity, and that for all samples combined, 41 isolates have QQ activity. Furthermore, heat treatment did not fully inhibit QQ activity in all isolates. In some isolates, QQ activity was lost after proteinase K treatment, while others remained able to quench QS. Therefore, it is likely that some isolates produce and secrete (a) heat-stable, low molecular weight inhibitory compound(s).     

Targeting Acyl Homoserine Lactones (AHLs) by the quorum quenching bacterial strains to control biofilm formation in Pseudomonas aeruginosa

Navigating novel biological strategies to mitigate bacterial biofilms have great worth to combat bacterial infections. Bacterial infections caused by the biofilm forming bacteria are 1000 times more resistant to antibiotics than the planktonic bacteria. Among the known bacterial infections, more than 70% involve biofilms which severely complicates treatment options. Biofilm formation is mainly regulated by the Quorum sensing (QS) mechanism. Interference with the QS system by the quorum quenching (QQ) enzyme is a potent strategy to mitigate biofilm. In this study, bacterial strains with QQ activity were identified and their anti-biofilm potential was investigated against the Multidrug Resistant (MDR) Pseudomonas aeruginosa. A Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136-based bioassays were used to confirm the degradation of different Acyl Homoserine Lactones (AHLs) by QQ isolates. The 16S rRNA gene sequencing of the isolated strains identified them as Bacillus cereus strain QSP03, B. subtilis strain QSP10, Pseudomonas putida strain QQ3 and P. aeruginosa strain QSP01. Biofilm mitigation potential of QQ isolates was tested against MDR P. aeruginosa and the results suggested that 50% biofilm reduction was observed by QQ3 and QSP01 strains, and around 60% reduction by QSP10 and QSP03 bacterial isolates. The presence of AHL degrading enzymes, lactonases and acylases, was confirmed by PCR based screening and sequencing of the already annotated genes aiiA, pvdQ and quiP. Altogether, these results exhibit that QQ bacterial strains or their products could be useful to control biofilm formation in P.aeruginosa.     

Beyond the oral microbiome

The human oral microbiome currently comprises 600-700 taxa, but estimates suggest that overall species numbers may turn out to be higher (～1200). Within the oral cavity, groups of microbial species become arranged into surface-localized communities that vary considerably in composition according to sites of establishment. Factors such as nutrient availability, pH, toxic metabolites, shear forces and host conditions contribute to modelling the structure and activities of these oral microbial communities. With development of more rapid and accurate molecular techniques it has become possible to begin to characterize the genome contents of individual communities. However, understanding the phenotypic interactions between cultivable microorganisms within communities is essential in order to complement the genomic data. This will then enable construction of microbial community interactomes, incorporating genomic and spatial information with functional knowledge of physical and metabolic interplays between the microorganisms. Enlightenment of the changes in genome composition and phenotypic interactions as functions of niche, time and intrusions will help towards developing better means of manipulating communities for host benefit.     

Developing next generation antimicrobials by intercepting AI-2 mediated quorum sensing

Bacteria have been evolving antibiotic resistance since their discovery in the early twentieth century. Most new antibiotics are derivatives of older generations and there are now bacteria that are virtually resistant to almost all antibiotics. This poses a global threat to human health and has been classified as a clinical “super-challenge”, which has necessitated research into new antimicrobials that inhibit bacterial virulence while minimizing selective pressures that lead to the emergence of resistant strains. Quorum sensing (QS), the process of population dependent bacterial cell-cell signaling, can accelerate bacterial virulence and is an increasingly interesting target for developing next generation antimicrobials. Most QS inhibitors target species-specific signals, such as acylhomoserine lactones (AHLs) and oligopeptides. Methodologies for intercepting the cross-species signal, autoinducer-2 (AI-2), have only recently emerged. We review these strategies to prevent the relay of the AI-2 signal amongst pathogens, including Escherichia coli, Salmonella enterica serovar Typhimurium, Vibrio cholerae and Pseudomonas aeruginosa. Inhibition mechanisms are categorized based on the target (i.e., enzymes for signal generation, the signal molecule itself, or the various components of the signal transduction process). The universal nature of the AI-2 signal imparts on its inhibitors the potential for broad spectrum use.     

Unravelling the core microbiome of biofilms in cooling tower systems

In this study, next generation sequencing and catalyzed reporter deposition fluorescence in situ hybridization, combined with confocal microscopy, were used to provide insights into the biodiversity and structure of biofilms collected from four full-scale European cooling systems. Water samples were also analyzed to evaluate the impact of suspended microbes on biofilm formation. A common core microbiome, containing members of the families Sphingomonadaceae, Comamonadaceae and Hyphomicrobiaceae, was found in all four biofilms, despite the water of each coming from different sources (river and groundwater). This suggests that selection of the pioneer community was influenced by abiotic factors (temperature, pH) and tolerances to biocides. Members of the Sphingomonadaceae were assumed to play a key role in initial biofilm formation. Subsequent biofilm development was driven primarily by light availability, since biofilms were dominated by phototrophs in the two studied ‘open’ systems. Their interactions with other microbial populations then shaped the structure of the mature biofilm communities analyzed.     

The volatile microbiome

The first detailed temporal study of the human microbiome shows that individual body habitats exhibit surprising variation over time yet maintain distinguishable community structures.     

Complex pattern formation of marine gradient bacteria explained by a simple computer model

We report on the formation of conspicuous patterns by the sulfide-oxidizing bacterium Thiovulum majus and a recently described vibrioid bacterium. These microaerophilic bacteria form mucus veils on top of sulfidic marine sediment exhibiting regular spaced bacterial patterns (honeycombs, interwoven bands, or inverse honeycombs). A simple qualitative computer model, based on chemotaxis towards oxygen and the ability of the bacteria to induce water advection when attached, can explain the formation of the observed patterns. Our study shows that complex bacterial patterns in nature can be explained in terms of chemotaxis and resource optimisation without involvement of cell-cell signalling or social behavior amongst bacteria.     

„Small Talk“

The silent communication of bacteria Bacteria communicate via small diffusible molecules, a process that microbiologists refer to as quorum sensing. These language molecules are released by the bacteria in the environment and are then sensed by their neighbours via specific receptors. Thus, the community can arrange and adapt specific phenotypes in dependence on the cell count termed quorum. Due to the different structures and modifications of the communication molecules bacteria have evolved different languages and dialects, which can in addition give information about time and venue. Moreover, bacteria have small talk with their hosts such as animals, plants and yet humans. Since communication is a prerequisite for the infection of hosts by pathogenic bacteria, the molecular components of the bacterial communication are promising candidates as targets for badly needed new antimicrobial drugs.     

Quorum sensing intervened bacterial signaling: Pursuit of its cognizance and repression

Bacteria communicate within a system by means of a density dependent mechanism known as quorum sensing which regulate the metabolic and behavioral activities of a bacterial community. This sort of interaction occurs through a dialect of chemical signals called as autoinducers synthesized by bacteria. Bacterial quorum sensing occurs through various complex pathways depending upon specious diversity. Therefore the cognizance of quorum sensing mechanism will enable the regulation and thereby constrain bacterial communication. Inhibition strategies of quorum sensing are collectively called as quorum quenching; through which bacteria are incapacitated of its interaction with each other. Many virulence mechanism such as sporulation, biofilm formation, toxin production can be blocked by quorum quenching. Usually quorum quenching mechanisms can be broadly classified into enzymatic methods and non-enzymatic methods. Substantial understanding of bacterial communication and its inhibition enhances the development of novel antibacterial therapeutic drugs. In this review we have discussed the types and mechanisms of quorum sensing and various methods to inhibit and regulate density dependent bacterial communication.     

革兰氏阴性细菌LuxR/I型群体感应抑制剂研究进展

摘要：细菌群体感应（Quorum sensing, QS）被视为对抗细菌感染与解决细菌耐药性问题的新靶点。以AHLs为信号分子的LuxR/I型群体感应系统广泛存在于革兰氏阴性菌包括多种临床致病菌中,因此寻找LuxR/I型群体感应抑制剂（Quorum sensing inhibitors, QSIs）是研发抗革兰氏阴性致病菌药物的重要途径。迄今为止,已知的LuxR/I型小分子QSIs来源包括化学合成、天然产物与已知药物库的化合物,大分子则包括群体感应淬灭酶与群体感应淬灭抗体。本文总结了近年来LuxR/I型QSIs研究进展,为新型抗菌药物研发提供理论依据。     

Characteristics of human oral microbiome and its non-invasive diagnostic value in chronic kidney disease

Background: Morbidity of chronic kidney disease (CKD) is increased, with many complications and high mortality rates. The characteristics of oral microbiome in CKD patients have not been reported. This study aims to analyze the oral microbiome, and to demonstrate the potential of microbiome as noninvasive biomarkers for CKD patients.Methods: The study collected 253 oral samples from different regions of China (Central China and East China) prospectively and finally 235 samples completed Miseq sequencing, including 103 samples from CKD patients and 132 healthy controls (HCs).Results: Compared with HCs (n=88), the oral microbial diversity in CKD patients (n=44) was increased. Fourteen genera including Streptococcus, Actinomyces and Leptotrichia were enriched, while six genera including Prevotella and Haemophilus were decreased in CKD patients. Moreover, 49 predicted microbial gene functions including arginine metabolism and tryptophan metabolism increased, while 55 functions including Ribosome and DNA repair recombination proteins decreased. Furthermore, correlation analysis demonstrated that 38 operational taxonomic units (OTUs) were closely related to 5 clinical indicators of CKD. Notably, 7 optimal biomarkers were identified using random forest model, and the classifier model respectively reached an area under the curve (AUC) of 0.9917 and 0.8026 in the discovery and validation phase, achieving a cross-region validation.Conclusions: We first illustrated the characteristics of the oral microbiome of patients with CKD, identified the potential of oral microbial makers as noninvasive tools for the diagnosis of CKD and achieved cross-region validation.     

N-acylhomoserine lactone-degrading bacteria isolated from hatchery bivalve larval cultures

Quorum sensing (QS) systems, which depend on N-acylhomoserine lactone (AHL) signal molecules, mediate the production of virulence factors in many pathogenic microorganisms. One hundred and forty-six bacterial strains, isolated from a bivalve hatchery, were screened for their capacity to degrade five synthetic AHLs [N-butyryl-dl-homoserine lactone (C₄-HSL), N-hexanoyl-dl-homoserine lactone (C₆-HSL), N-octanoyl-dl-homoserine lactone (C₈-HSL), N-decanoyl-dl-homoserine lactone (C₁₀-HSL) and N-dodecanoyl-dl-homoserine lactone (C₁₂-HSL)] using well diffusion agar-plate assays with three biosensors, Chromobacterium violaceum CV026, C. violaceum VIR07 and Agrobacterium tumefaciens NTL4 (pZLR4). The results of these assays led to our choosing four strains (PP2-67, PP2-459, PP2-644 and PP2-663) that were able to degrade all five synthetic AHLs, thus showing a wide spectrum of quorum quenching (QQ) activity. We subsequently confirmed and measured the QQ activity of the four strains by high-performance liquid chromatography plus mass-spectrometry analysis (HPLC–MS). One of the strains which showed the highest AHL-degrading activity, PP2-459, identified as being a member of the genus Thalassomonas was chosen for further study. Finally, using thin-layer chromatography (TLC), we went on to confirm this strain's capacity to degrade the AHLs produced by other non-pathogenic and pathogenic bacteria not taxonomically related.     

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。