| This thesis focused on AHL-lactonase that can block the bacterial quorum sensing by hydrolyzing AHL-lactone and greatly attenuate the disease caused by many bacterial pathogens employing quorum sensing to regulate the expression of virulence genes. The results are summarized as following:1. Activity of AHL-lactonase against soft rot caused by Erwinia carotovora.Different Bacillus thuringiensis strains have distinct activity to protect potato slice from soft rot caused by E. carotovora SCG1. B. thuringiensis strains H38 and H42 with high activity were choiced to clone aiiA gene. The purified AHL-lactonase expressed in E.coli BL21(DE3) greatly attenuated the pathogenicity of E. carotovora SCG1.To investigate the potential target of AHL-lactonase, the AHL signal was detected from bacteria and fungi. The strong AHL signal was observed from plant pathogens except for Xanthomonas campestris with faint AHL signal. While no AHL signal was found in gram-positive bacteria and any fungus.2. Ability of B. thuringiensis strains over-expressing AHL-lactonase to protect Amorphophallus konjac from soft rot disease caused by E. carotovora pv. carotovora.Engineering B. thuringiensis BMB686 and BMB3439 was used to protect A. konjac from soft rot disease in 2003, 2004 and 2005 year. Common germicides and water acted as control. The results showed that the relative control effect of engineering B. thuringiensis reached 40-45% in new A. konjac field and 35-40% in old A. konjac field (cultivated for one year). The best relative control effect of germicides reached 50% and those of so many germicides were lower than 40%.3. Transform to A. konjac with alterated aiiA gene via Agrobacterium.Genetic transformation system of Amorphophallus was established via. Agrobacterium. First, the tissue culture conditions of A. konjac were optimized. Second, the aiiA gene was alterated and transformed to A. konjac. The concentration of Hygromycin, the... |
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