| Summary: | 碩士 === 國立屏東科技大學 === 生物科技系所 === 106 === Quorum sensing (QS) is a mechanism in which gram negative bacterial pathogens sense their population density through acyl homoserine lactones (AHL) and regulate the expression of virulence factors. Enzymatic degradation of AHL by lactonases known as quorum quenching (QQ) is thus a potential strategy for attenuating QS regulated bacterial infections. Pectobacterium carotovorum is an important broad host range, soft rot causing phytopathogen with multiple modes of infection. AHL mediated quorum sensing mechanism plays a pivotal role in the pathogenesis of P.carotovorum by regulating its major virulence enzymes that degrade plant cell well. Here, the disruption of quorum sensing as a strategy for biocontrol of P.carotovorum is proposed especially in the light of rising antimicrobial resistence. Bacillus based biocontrol agents have been found useful in management of bacterial and fungal plant diseases. Additionally, they are known to produce AHL lactonase that inactivates AHL signaling in quorum sensing. AHLs lactonase is encoded by aiiA gene. In this study, AHL lactonase recombinant protein from Bacillus sp strain ER1 can inactivate AHL of P.carotovorum. The purified protein of E.coli BL21(DE3)/pET28a/aiiA resulted in a single band of 34 kDa molecular weight and E.coli BL21(DE3)/pET29a/aiiA is 36 kDa. Multiple sequence alignment of the amino acid sequence of AiiA show that it belongs to the metallo-hydrolase like MBL-hydrolase fold superfamily. Furthermore, in this study AHL lactonase recombinant protein from Bacillus sp strain ER1 can degrade AHL produced by Pectobacterium carotovorum, a common cause of soft rot. This QQ activity causes a decrease in production of plant cell wall degrading enzymes of P.carotovorum and attenuates symptoms of soft rot in experimental infection of potato. The root colonisation ability studies of prevention of mung bean spoilage further demonstrate that the AHL lactonase recombinant protein from Bacillus sp strain ER1 has high potential to reduce the disease
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