Inhibition Of Lux Quorum Sensing System Of V.fischeri By Two Kinds Of New Inhibitors

Quorum sensing is the regulation of gene expression in response to fluctuations in cell-population density.Quorum sensing bacteria produce and release chemical signal molecules called autoinducers that increase in concentration as a function of cell density.The detection of a minimal threshold stimulatory concentration of an autoinducer leads to an alteration in gene expression.During environment treatment,the use of bacteria is very important.On one hand,we could purify environment by impairing the pathogenicity of bacteria;on the other hand,we could do the environmental bioremediation by using the ability of bacteria to decompose the contamination.Therefore,do further research in the control relationship between the quorum sensing and the phenotypes of bacteria are helpful to exert the function of bacteria in environment treatment,which is meaningful.Vibrio fischeri is the bacteria in which quorum-sensing was discovered,first described and best-studied.And although each of the known systems has unique features,the Lux quorum sensing system of V. fischeri is considered the model.So it is meaningful to find quorum sensing inhibitors on Lux quorum sensing system of V.fischeri although it is not a pathogen.V.fischeri belongs to the Vibrionaceae,a large family of marine gamma-proteobacteria that includes several dozen species known to engage in a diversity of beneficial or pathogenic interactions with animal tissue.V.fischeri is found in several niches in the marine environment and exists naturally either in a free-living planktonic state or as a symbiont of certain luminescent fish or squid.The bacteria colonise specialised light organs in the fish or squid,which cause them to bioluminesce.Luminescence in the fish or squid is thought to be involved in the attraction of prey or even as camouflage.The ability of V.fischeri cells to produce bioluminescence results from the expression of the lux operon,a small cluster of genes that have been well studied in this organism,and have been adapted to many uses in biotechnology.In fact, many gram-negative pathogens control the expression of virulence factors, secretion of extracellular protease,pectinase,and rhamnolipid,and biofilm formation via the quorum sensing system.Consequently, quorum-sensing disruption has been suggested as a promising new strategy to control microbial infection.In this work,we have test three different kinds of compounds and demonstrated their infectory effect on Lux quorum sensing system transformed to Escherichia coli.First,we find that the natural quorum sensing inhibitor halogenated furanone is also effective on Lux quorum sensing system.Second,we synthesized a series of N-acyl cyclopentylamides with acyl chain lengths ranging from 4 to 11 and estimated their inhibitory effects on Lux quorum sensing system.All of these molecules had showed some extent of inhibitory effect and N-Pentanoyl cyclopentylamide(C5-CPA),N-Hexanoyl cyclopentylamide (C6-CPA),N-Heptanoyl cyclopentylamide(C7-CPA),N-Octanoyl cyclopentylamide(C8-CPA),.N-Nonanoyl cyclopentylamide(C9-CPA), N-Decanoyl cyclopentylamide(C10-CPA) inhibited Lux quorum sensing system strongly.The most effective inhibitors are C6-CPA,C7-CPA and C8-CPA,which inhibited luminescence about 90%at a final concentration of 100μM.We also compared the inhibitory effect of halogenated furanone and C6-CPA(one of the most effective inhibitors). And our data indicated that these molecules were potent inhibitors on Lux quorum sensing system and more effective than halogenated furanone. Third,we found thatα-cyclodextrin(α-CD),β-cyclodextrin(α-CD),γ-cyclodextrin(γ-CD) and all can inhibit Lux quorum sensing system.γ-CD turned out to be the most effective one in these cyclodextrins(CD). We also analyzed the mechanism of the quorum sensing inhibition of cyclodextrin and found that both the side chain and the size of circle radius.All the researches will helpful for the Gram-negative bacterial pathogen inhibition in environment and provide new ideas and ways for using this bacterium in environmental bioremediation.