Study On Quorum Quenching Effect Of Pediococcus Pentosaceus YF-8 On Aeromonas Sobria

Aeromonas sobria is one of the common dominant spoilage bacteria in aquatic products,and its spoilage mechanism is closely related to the quorum sensing(QS)system,so finding active substances that interfere with the QS of A.sobria can be effectively controlled its pathogenic ability.Lactic acid bacteria are widely used in the food field as a safe,green,and efficient biological agent,but their research as a quorum quencher is rarely reported at home and abroad.In this paper,we screened lactic acid bacteria with degrading activity to N-acylated homoserine lactones(AHLs)from fermented food,fish intestines and other environments,and carried out physiological,biochemical reactions and 16 S r DNA sequencing to identify them.We studied the effect of YF-8 crude extract on A.sobria casein,extracellular polysaccharides,hemolytic activity,siderophore and other virulence factors,biofilm formation,clustering and migrating motility,and Lux I/Lux R gene expression.Analyzing the quenching effect of strain YF-8 on the rot-causing ability of A.sobria.Using sterile salmon pieces as a carrier,the effect of strain YF-8 on the rot-causing ability of A.sobria was studied from an in vitro model.The main research work and conclusions were as follows:1.The 96-well plate method combined with the Oxford cup punch method was used to screen 184 strains of lactic acid bacteria to obtain a strain YF-8 that can degrade A.sobria AHLs,and the degradation activity is close to 100%.The strain was isolated from Chaoyang pickles and was identified as Pediococcus pentosaceus after physiological and biochemical reactions and 16 S r DNA sequencing analysis.The enzymatic activity of strain YF-8 was measured under acidic and neutral conditions,and the effect of AHLs-lactonase was excluded.At the same time,it was found that the enzymatic activity of strain YF-8was located in the cell-free supernatant.The minimum inhibitory concentration(MIC)of the crude extract of strain YF-8 against A.sobria is 8.0 mg/m L.The sub-minimum inhibitory concentration of 2.0,4.0 and 6.0 mg/m L does not affect the growth of A.sobria,and can also degrade the production of Cyanobacteria CV026,which is dose-dependent.2.To study the effect of the crude extract of strain YF-8 on the production of virulence factors such as A.sobria casein,extracellular polysaccharides,hemolytic activity,and siderophore,and its influence on flagella-mediated clustering and swimming motility.And for the formation of biofilms and the removal of pre-formed biofilms,the regulatory effect of this strain on Lux I/R gene expression in the QS system was further analyzed.The results showed that: after treatment with YF-8 crude extracts with sub-minimal inhibitory concentrations of 2.0,4.0 and 6.0 mg/m L,the inhibitory rates on A.sobria casein,extracellular polysaccharides,hemolysis and siderosin were 9.6%-32.72%,17.91%-58.09%,19.21%-51.49%,19.04%-44.35%,respectively.The inhibitory rate of 6.0mg/m L YF-8 crude extract on cluster migration is close to 100%.The results of q RT-PCR analysis found that the 6.0 mg/m L YF-8 crude extract reduced the relative expression levels of Lux I and Lux R by 69.48% and 80.76%,indicating that the transcription levels of Lux I and Lux R genes were interfered by YF-8 CE.The 96-well plate method,optical microscopy and scanning electron microscopy results show that the YF-8 CE of sub-MIC can significantly inhibit and eliminate the formation and preformed biofilm of A.sobria.3.By measuring the total number of bacterial colonies,water holding capacity,p H,TBA,TVB-N and other indicators of salmons treated with different treatments when refrigerated at 4 ?,it was verified that the crude extract of Pediococcus pentosaceus YF-8had a mild gas list for important spoilage bacteria in salmon.Inhibitory effect of spores causing decay.The results showed that the total number of bacterial colonies,TBA and TVB-N of salmon treated with different treatments showed a continuous increasing trend during the cold storage at 4 ?,the water holding capacity gradually decreased,and the p H generally showed a "V"-shaped change.YF-8 treatment can effectively delay the increase in p H,TBA and TVB-N of salmon and the decrease in water holding capacity.After YF-8was co-cultured with A.sobria,the rot-causing ability of A.sobria on salmon was reduced.Compared with the control group,it could extend the shelf life by 2d and 4d.