Detection Of Autoinducer And Functional Analysis Of Its Synthesis Gene LuxI In Acidovorax Avenae Subsp. Citrulli

Bacterial fruit blotch(BFB),caused by Acidovorax avenae subsp,citrulli,is one of the most devastating and difficult-to-control diseases.Recently,this disease is becoming more and more serious in China,and has caused great damage on growth of Hamirmelons and economy.Till now,many researches focused on improving the BFB management, including chemical seed treatment and biological control.Little information on the virulence determinants of this pathogen was availableIn this study,we detected the autoinduer(AI) activity in the supernant of A.avenae subsp,citrulli by a ultrasensitive AHL bioassay strain JZA1(pJZ372)(pJZ384)(pJZ410). The results of quantitative LacZ activity and qualitative TLC detection showed that A. avenae subsp,citrulli xjL12 could produce high active and one type AHLs(C₈-AHL).In addition,other 56 strains were also selected for AHL bioasaay.Among them,39 strains had the ability to produce AI-1(AHLs),and 18 strains were showed no AHL-activity.Together, these results indicated that quorum sensing system was existed in A.avenase subsp,citrulli, but different in the different strains.A search of the genome of A.avenae subsp,citrulli revealed that a acluxI homologue to that of Pesudomonas syringe pv.tomato DC3000 was found.By PCR method,the acluxI homologue was amplified from AHL-producing strain xjL12,and was expressed in Escherichia coli DH5α.Interestingly,the AI-1-deficient E.coli DH5αhad the ability to produce AHLs by expression of luxI homologue from strain xjL12.Furthermore,the acluxI homologue was knocked out by recombinant homologue technique The results of AHL detection and pathogenicity test showed that the acluxI mutant had no AHL activity and showed significant reduction of virulence on fruit and seedlings of Hamimelon.These results revealed that Quorum sensing system might play a key role in the virulence of A. avenae subsp,citrulli.