Research On Quorum Sensing Of Serratia Grimeii And The Inhibition Of Its AHLs

(1)A strain producing quorum sensing signals was isolated from spoilage Scophthalmus maximus.The strain was serratia grimesii SG-05 according to its physiological-biochemical characteristics and 16S rRNA gene analysis.AHLs were analyzed by the agar diffusion method using Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136.The meteorological chromatography-mass spectrometry was established,and signaling molecules standard qualitative was supplemented to measure the kinds of content in the crude extract of strain SG-05.The results showed that the strain could activate Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136,respectively.The strain SG-05 was detected including at least two AHLs,C6-HSLand C8-HSL.(2)The effects of bacterial growth stages and the strain SG-05 producing AHLs at different culture conditions were also investigated.With the extension of culture time,the activities of AHLs increased in the initial period and then decreased in a concentration-dependent manner.The optimal salinity for strain SG-05 to produce AHLs was 0.25%to 1.5%NaCl.The secretion of AHLs was promoted when they were grown in the different carbon sources(glucose,fructose,xylose,maltose)and the optimal carbon source for strain SG-05 to produce AHLs was fructose.The optimal nitrogen source and salinity for strain SG-05 to produce AHLs was tryptone.The ability of strain producing AHLs was suitable to weak acid and neutral environment,the optimum pH secreting AHLs was pH 6.0.The study showed that sensing signals were dramaticallly regulated by bacterial densities as well as outer environmental factors.(3)The relationship between different kinds of AHLs and biofilm of Serratia grimeii SG-05 were further studied,and the extracellaluar proteases of Serratia grimeii SG-05 was determined by skim milk medium.Using SDS-polyacrylamide gel electrophoresisi(SDS-PAGE),Serratia grimeii SG-05 was added to the extracts from myofibrilar protein and sarcoplasmic protein,and AHLs were found to mediate the biodegradation process of protein extracts.The regulation of quorum sensing to the spoilage of Serratia grimeii SG-05 was studied by measuring the sensory scores,total viable counts,TBA and color changes of fish juice.The results showed that exogenous AHLs could also promote biofilm formation of Serratia grimeii SG-05,especially C6-HSL,which promoted biofilm formation significantly at 36 h.Serratia grimeii SG-05 could secrete extracellaluar proteases and be regulated by C4-HSL.SG-05 had a promote effect on protein degradation.Especially AHLs had a most promote effect on sarcoplasmic protein in a concentration-dependent manner.Serratia grimeii SG-05 had an impact on the spoilage of fish juice,and C4-HSL could accelerate the rate of spoilage,the quorum sensing could regulate the spoilage ability of SG-05 by AHLs.(4)CDs could accept the acyl chains of AHLs and that AHL-CD inclusion complexes could form in aqueous media.CDs could reduce violacein production in C.violaceum 026,and inhibit the biofilm formation and CASAD of Serratia grimeii.Total viable counts of turbot block dealt with CDs and grape seed extract,were lower than other samples.TVB-N,pH value were also lower than other samples.In addition,recombination of CDs and GSE extract could enhance binding force of water.Therefore,recombination of QSI and bacteriostatic agent used in aquatic preservation had certain feasibility.