Study On Degradation Techniques On Transgenic Organisms Of Bt Toxin

Using Bacillus thuringiensis and straw of Bt transgenie rice as materials, influence of UV radiation,⁶⁰Co radiation, enzymes and microorganisms isolated from soil on degradation of Bt toxin was studied. Results were as follows.(1) UV radiation could degrade Bt toxin in Bacillus thuringiensis, and UV lamp power, distance from protein to UV light as well as irradiation time were factors contributing to degradtion rate. The degradtion rate increased with UV lamp power and distance grow down, while irradiation time decreasing.(2) 60Co radiation could degrade Bt toxin in Bacillus thuringiensis, and Bt degration was enhanced with dose of 60Co increasing. However, there was no significant change on degration of Bt when the dose exceeding 2 kGy.(3) Purified Bt toxin could not be to degraded basically within 6 h. In addition, factors such as temperature and shocking has no significant impact on degration of Bt within 6 h.(4) Under optimum conditions of enzymes, all the seven proteases selected could degrade purified Bt toxin. However, only bromelain, neutral proteinasc and alkaline protease could completely degrade Bt toxin at 30℃,pH 7.0. In view of price and application, neutral proteinasc was selected for further study. Bt toxin could be completely degraded by adding 12 U protease to 1 ml of saturated Bt toxin solution and making them react for 20 min at 30℃. In addition, neutral proteinasc could also degrade Bt toxin in Bt transgenie rice, and degradation rate was proportional to ratio of enzyme and substrate, hydrolysis temperature as well as hydrolysis time.(5) A efficient bacteria for Bt toxin degradation was sreened and coded as FJB3. Bt toxin could be completely degraded by adding 0.05 ml of fermentation supernatant of FJB3 which had been cultivated for 24 h to 9.95 ml of saturated Bt toxin solution and making them react for 4 h at 30℃, In addition, FJB3 could also degrade Bt toxin in Bt transgenie rice. The degradation rate of Bt toxin reached the highest level at 25°C and degradation rate increased with fermentation time increasing. The degradation rate reached 59.63% and 83.53% after 5 and 25 d fermentation of FJB3 respectively.