Study On The Influence Factors Of The Degradation Of Bt Protein In Soils

Transgenic Bt crops obtained by genetic engineering had greatly relieved the damage caused by insect pest,thereby improved the yield of crops and lessened the application of pesticide.However,the potential ecological risk brought by the large-scale commercialization of transgenic Bt crops has been highly concerned by the scholars from domestic and abroad,since the bioactivity and residue of applied Bt protein into soil are the important parameters to appraise their protential risk to non-objective species and fate of environment.In this experiment,we applied the purified Bt protein into soil to simulate the degradation of Bt protein in soil under natural conditons and study the effect of sterilization,temperature,pH,initial concentration on the degradation of Bt protein by ELISA for the sake of providing scientific basis for the evaluation of eco-environment risks caused by transgenic Bt crops.The main results and conclusions are as follows:1) The initial content of Bt protein in red soil,yellow brown soil,yellow cinnamon soil and latosol were different and the values changed after the soils were either sterilized or added with acid or alkali.The sterilization made the content of Bt protein decrease but acidification/alkalization brought it to increase.Moreover,the content of Bt protein in the soil treated with alkali attained to the maximum.2) The DT₅₀ of non-sterilized and sterilized red soil was 5.2 and 11.2 days respectively,while for DT₉₀ they were 23.1 and 39.4;the DT₅₀ of non-sterilized and sterilized yellow brown soil was 1.5,4.1 days respectively,and for DT₉₀ they were 5.2 and 17.6.Apparently,the DT₅₀ and DT₉₀ of Bt protein in non-sterilized soil were longer than those in sterilized soil respectively.As a conclusion,Bt protein in non-sterilized soil degraded faster than that in sterilized soil and the sterilization slowed down the degradation of Bt protein in soil.3) The DT₅₀ of Bt protein in red soil was 8.1,5.2,5.4 days and the DT₉₀ was 32.9, 23.1,22.3 days in accordance with the temperature at 5℃,25℃,40℃respectively.The DT₅₀ and DT₉₀ of Bt protein at 5℃were longer than those at 25℃and 40℃.The DT₅₀ of Bt protein in yellow brown soil was 7.9,1.5,1.6 days and the DT₉₀ was 23.9,5.2,5.6 days under the temperature of 5℃,25℃,40℃respectively.The comparison of DT₅₀ and DT₉₀ at different temperature is 5℃＞40℃≈25℃.Obviously,both in the two experimental soils,the residual time of Bt protein at 5℃was longer than that at 25℃or 40℃denoting that high-temperature will accelerate the degradation of Bt protein in soil. The DT₅₀ of Bt protein in distilled water were 5.0,0.9,2.2 days and the DT₉₀ were 15.8, 3.1,7.8 days when the temperature was 5℃,25℃,40℃correspondingly.The DT₅₀ and DT₉₀ of Bt protein at 5℃were evidently longer than the counterparts at 25℃and 40℃. On the other hand,the DT₅₀ and DT₉₀ at 25℃were evidently shorter than those at 40℃. Among the three different temperatures,25℃is the optimal temperature for the degradation of Bt protein in distilled water.4) The DT₅₀ of Bt protein in yellow cinnamon soil was 103.2,42.6,18.4 days and the DT₉₀ was 362.5,162.9,76.5 days when the pH was 4.32,5.31,6.62 respectively.The comparison for DT₅₀ and DT₉₀ of Bt protein in yellow cinnamon soil under different pH conditions was pH4.32＞pH5.31＞pH6.62 illuminating that the higher pH came to the faster degradation of Bt protein within the pH range of 4.32-6.62 in yellow cinnamon soil.5) The DT₅₀ of Bt protein in latosol was 102.9,6.6,32.6 days and the DT₉₀ was 395.5,33.5,116.0 days when the pH was 3.75,4.47,5.17 respectively.The comparison of DT₅₀ and DT₉₀ of Bt protein in latosol attributed to different pH was pH3.75＞pH5.17＞pH4.47.We could draw a conclusion that the higher pH can accelerate the degradation of Bt protein,but the degradation speeds up first and then slows down with the pH range of 3.75-5.17 in latosol.6) After adding the Bt protein at three different initial concentrations into the experimental soils respectively,the Bt protein residue rised with the increase of initial concentration at the same sampling time.The DT₅₀ of Bt protein in yellow cinnamon soil was 13.7,22.9,28.3 days at the three different initial concentrations of 5.0,10.0,20.0μg g^-1 soil respectively and for the DT₉₀ they were 50.2,80.5,105.3 days;for the DT₅₀ of Bt protein in latosol they were 2.5,6.2,9.2 days and for the DT₉₀ they were 8.4,30.1,39.6 days.The DT₅₀ and DT₉₀ of Bt protein in the two experimental soils increased with the mounting initial concentrations.The higher concentration of Bt protein contributed to the longer residual time demonstrating that the Bt protein in soil was difficult to eliminate by degradation.