The Research Of Quorum Sensing Mechanism's Analysis And Its Inhibition In Serratia Marcescens AS-1

By producing a kind of diffusible, small molecular weight signal molecule, bacteria could apperceive the thalli density and communicate with each other. The mechanism that according to the concentration of the signal molecule to feel the density of the bacteria, control a kinds of gene expressions, such as virulence factor production, biofilm formation, release of antibiotic and swarming motility, is called quorum sensing. 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.In gram-negative bacteria, there is the LuxI-LuxR-type quorum sening system. The protein LuxI produces the N-acylhomoserine lactone (AHL) as quorum sensing signal molecule and AHLs bind LuxR to regulate a series of phenotypes. Serratia marcescens is a gram-negative bacterium and widely exists in air, soil and water. The investigation of literature shows that research on the quorum sensing of S. marcescens is seldom in china and abroad. In this research, we use S. marcescens AS-1 as the sample of S. marcescens, analysis its quorum sensing mechanism in detail and do some researches on its inhibition.S. marcescens AS-1 had the LuxI/LuxR homologues, called SpnI/SpnR. In this study, we disrupted AHL-synthesis gene (spnI) and AHL-receptor gene (spnR) in AS-1 for constructing the spnI gene defaulted mutant, named AS-â–³I, the spnR gene defaulted mutant, named AS-â–³R and both of the spnI gene and the spnR gene defaulted mutant, named AS-â–³I/â–³R. By comparing a series of phenotypes between wild type and its mutants we find that in S. marcescens AS-1, SpnI synthesizes N-hexanoyl-L-homoserine lactone (C₆-HSL) and N-(3-oxohexanoyl)-L-homoserine lactone (3-oxo-C₆-HSL) as its signal molecule which bind SpnR could regulate the phenotypes of prodigiosin production, swarming motility and biofilm formation and the SpnR acted as a negative regulator of quorum sensing.Both the natural inhibitor of quorum sensing halogenated furanone and the artifical inhibitor of quorum sensing N-acyl cyclopentylamide (Cn-CPA) could effectively inhibit the quorum sensing in many bacteria. We estimated the inhibitory effect on prodigiosin production, swarming motility and biofilm formation in AS-1 by halogenated furanone and a series of Cn-CPA with acyl chain lengths ranging from C₃ to C₁₁, the results showed that, on one hand, halogenated furanone had inhibitory effect on those phenotypes, on the other hand, One of a series of Cn-CPA with acyl chain lengths ranging from C₃ to C₁₁, N-nonanoyl-cyclopentylamide (C₉-CPA) also had inhibitory effect on those phenotypes. After more study, we demonstrated that compared with halogenated furanone, C₉-CPA was more effective, and C₉-CPA inhibited the quorum sensing of AS-1 by competing with AHLs to bind to LuxR homologue SpnR. As the C₉-CPA added at 200μmol/L the inhibition rate of prodigiosin production reached 87%. As the C₉-CPA added at 50μmol/L swarming motility of S. marcescens AS-1 almost disappeared and biofilm formation was also weakened.All the researches will helpful for the S. marcescens pathogen inhibition in environment and provide a new way and a new idea for using this bacterium in environmental bioremediation.