Characterization Of LuxRI-type Quorum Sensing Systems And Quorum Quenching In Serratia Plymuthica

An array of evidence established that many Gram-negative bacteria employ Quorum sensing(QS) systems to regulate gene expression in response to cell density using small diffusible signal molecules,N-acyl homoserine lactones(AHLs),and control diverse phenotypic traits,such as virulence and biocontrol factors production,secondary metabolites, release of antibiotic,motility and biofilm formation,in plant-associated bacteria.Serratia plymuthica strains HRO-C48(C48) and G3 were isolated from the rhizosphere of oilseed rape and the stem of wheat, respectively.They both displayed biocontrol potential to suppress several plant diseases due to production of chitinases,protease and pyrrolnitrin, as well as promoting plant growth by production of indole-3-acetic acid (IAA).On the one hand,we investigated the functions of the second quorum sensing system SpsRI in strain C48 using mutational analysis of the wild type C48 and mutants deficient in spsI or spsR and both.On the other hand,using quorum quenching strategy via heterologously expresstion of the AHL-degrading lactonase AiiA in the strain G3 to analyse the influence of N-acyl homoserine lactone(AHL)-mediated cell-to-cell communication on the biocontrol-related traits in S. plymuthica,resulting in abolished AHL accumulation.The major results achieved in detail are as follows:1) The genes of splIR and spsRI(GenBank accession nos.FJ919305 and FJ919306),two pairs of luxRI homologs in S.plymuthica G3 were cloned based on PCR amplication,and the related phylogenetic analysis was performed.2) Quorum quenching analysis of the wild type G3,quenching strain G3/pME6863 and the vector control G3/pME6000 demonstrated that AHL-depended QS systems positively regulated proteolytic and chitinolytic activities,antifungal activity and biofilm formation but had almost no influence on swimming motility.3) Mutational analysis of the wild type HRO-C48 and its mutants revealed that SpsI positively regulates protease production,antifungal activity,biofilm formation and swimming motility.But SpsR may act as a repressor.The data rising from this study is of profound theoretical and practical significance,and it will help to provide novel strategies to improve biocontrol effencicy and stability through genetic manipulation of bacterial QS signaling.