Studies On Ecological Risk Of Bacillus Thuringiensis β-exotoxin

To study the ecological risk of P-exotoxin, p-exotoxin was extracted from the culture supernatant of subsp.kurstaki and subsp.thuringiensis by a series of two-phase aqueous systems. The OD growth curve of P-exotoxin was determined by ultraviolet spectrophotometer. The insecticidal toxicity of p-exotoxin was demonstrated by bioassays of p-exotoxin against larvae of Dendrolimus superans (Butler). In order to provide the oretical evidence for the aplication security of B.t. biolobicals, the toxicity of P-exotoxin was assayed by effecting on Dendrolimus superans (Butler) in the field, the germination rates and the sprout lengths of the Larix seeds, the Egg parasitoids of Dendrolimus superans (Butler), microorganism in the soils under the Larix forest and on the grown of Larix sprout. Results of this experiments as follows:(1) Exotoxin was extracted from the culture supernatant of B.t. subsp.kurstaki and B.t. subsp.thuringiensis using a series of two-phase aqueous systems and identificated with ultraviolet spectrophotometer;that was proved P-exotoxin.(2) Bioassays of toxicity of P-exotoxin on larvae of Dendrolimus superans (Butler), the results show that the corrected mortalities of larvae of Dendrolimus superans (Butler) by using 100 and 200 times liquid of p-exotoxin from B.t.subsp.kurstaki ,are 57.1% and 28.5% respectively;the corrected mortalities of larvae of Dendrolimus superans (Butler) by using 100 and 200 times liquid of P-exotoxin from B.t.subsp.thuringiensis , are 49.9% and 7.1% respectively.(3) Assays of toxicity of P-exotoxin from B.t.subsp.kurstaki and B.t.subsp.thuringiensis by being applied in the forest .The result show that the corrected mortalities of larvae of Dendrolimus superans (Butler) by using 100 and 200 times liquid of P-exotoxin from B.t.subsp.kurstaki , are 69.7% and 18.6% respectively;the corrected mortalities of larvae of Dendrolimus superans (Butler) by using 100 and 200 times liquid of P-exotoxin from B.t.subsp.thuringiensis , are 65.5% and 16.3% respectively;the corrected mortalities of larvae of Dendrolimus superans (Butler) by using 100 and 200 times liquid of Bacillus thuringiensis,are 76.9% and 59.0% respectively.The variance analysis indicated that the difference is notability among B.t.subsp.kurstaki β-exotoxin,B.t.subsp.thuringiensis P-exotoxin and Bacillus thuringiensis,also in different concentrations.(4) The average germination rates of the seeds of Larix that dealed with 100 and 200 times liquid of P-exotoxin from B.t.subsp.kurstaki are 30 ±2.5%and 31.3±0.76%;thegermination rates of the seeds of Larix that dealed with 100 and 200 times liquid of β-exotoxin from B.t.subsp.thuringiensis are 30.2±2.02% and 31±2.78%;the average germination rates ofthe seeds of Larix that dealed with fresh water is 34.3± 1.04%.Compared with the contrast,the germination rates of the seeds of Larix that dealed with P-exotoxin are little lower,but the suppressive effect is not very obvious.The average sprout lengths of the seeds dealed with 100 and 200 times liquid of P-exotoxin from B.t.subsp.kurstaki are 2.1±0.36cm and 2.0±0.32cm;The average sprout lengths of the seeds dealed with 100 and 200 times liquid of p-exotoxin from B.t.thuringiensis are 2.6±0.15cm and 2.6±0.21cm;the average sprout length of the seeds dealed with contrast of fresh water is 3.2±0.15cm. Compared with the contrast,the sprout lengths of the seeds dealed with p-exotoxin are relatively shorter;P-exotoxin plays a suppressive role in the growth of Larix sprout,and the suppressive effect of P-exotoxin from B.t.subsp.kurstaki is more obvious than that from B.t.subsp.thuringiensis.(5) p-exotoxin has a killing effect to Telenomus tetratomus Thomson -. Ooencyrtus pinicolus Matsumura and Trichogramma dendrolimi Matsumura. Using 100 and 200 times liquid of P-exotoxin from B.t.subsp.kurstaki ,the corrected mortalities of Telenomus tetratomus Thomson respectively are 59.2% and 16.8%;Using 100 and 200 times liquid of P-exotoxin from B.t.subsp.thuringiensis ,the corrected mortalities of Telenomus tetratomus Thomson respectively are 49.7% and 7.0%. and the corrected mortalities of Ooencyrtus pinicolus Matsumura is between 3.1 %~74.1 %.(6) Isolating and purifying from the soils under the Larix forest,obtained 5 kinds of dominant fungus and 5 kinds of dominant bacteria, through morphological and molecular biology methods the fungus have been identified ,the fungus are Penicillium , Mucor, Alternaria and Trichoderna .The identification of bacteria are Bacillus sp.and Sphingomonas sp. ,but the othe three are being in identifying.(7) B.t.subsp.kurstaki and B.t.subsp.thuringiensis can repress the number of the population of fungus and bacteria in soils under the Larix forest,the effect on the 5 kinds of fungus dealed with different concentrations of p-exotoxin is extremely significant;the effect on the 5 kinds of bacteria dealed with different concentrations of P-exotoxin is not significant.