[Objective] To isolate highly insecticidal Bacillus thuringiensis strains from soil samples collected in Beijing Botanical Garden. [Methods] B. Thuringiensis strains were isolated from soil samples using temperature method. Comparison of plasmid DNA pattern by agarose gel electrophoresis was conducted to discriminate the types of the isolates, cryl - cry40 type genes were identified via PCR-RFLP method. SDS-PAGE was used to analyze insecticidal crystal proteins. Insecticidal activity of these isolates against Colaphellus bowringi larvae and Plu-tella xylostella larvae was assayed. [Results] One hundred and forty-nine soil samples were collected and 147 B. Thuringiensis isolates were obtained. The types of the isolates were divided into 12 types, and these isolates contained bipyramidal, square, spherical and irregular crystal, respectively. crylAa, crylAb, cryl Ac, crylAh, crylBa, cryl Be, crylla, cryl La, cry2Ab and cry7Aa type genes were found in 6 isolates, but the other cry gene-types were unknown. SDS-PAGE results showed that 9 isolates could express Cry proteins of 130 ku, 1 of 70 ku, 2 of 150 ku, and 3 of both 130 ku and 60 ku. Bioassay results of 12 isolates indicated that the isolate ZWY-7 was toxic to C. Bowringi larvae, and the isolate ZWY-9 had highly insecticidal activity to P. Xylostella larvae, but their cry gene-types were unknown. [Conclusion] The B. Thuringiensis strains spread widely in Beijing Botanical Garden, belonging to different types. We found 2 Bt strains which were highly insecticidal, and it is possible to find more novel genes.%[目的]从北京植物园采集的土壤样品中分离高毒力的苏云金芽胞杆菌.[方法]采用温度法筛选Bt菌株,比对大质粒DNA图谱,区分不同类型的Bt菌株,PCR-RFLP方法对cry1～cry40类基因型进行鉴定,SDS-PAGE分析杀虫晶体蛋白,测定Bt分离株对大猿叶甲、小菜蛾幼虫的杀虫活性,筛选出高毒力的菌株.[结果]从149份土壤样品中分离出147株Bt,分为12种类型,含有菱形、方形、球形和不规则等晶体类型；6株菌中分别含有fry1Aa、cry1Ab、cry1Ac、cy1Ah、cry1Ba、cry1Be、cry1Ia、cry1La、cry2Ab和cry7Aa等基因类型,其余6株中不含有已知基因.有9株表达约130 ku蛋白,1株表达约70 ku蛋白,2株表达约150 ku蛋白,有3株既表达130 ku蛋白又表达60 ku蛋白；发现一株对大猿叶甲具有较高毒力的菌株ZWY-7,1株对小菜蛾有高毒力的菌株ZWY-9,2株菌都没有检测到已知基因型.[结论]北京植物园中Bt分布广泛,类型多样,其中发现两株高毒力的菌株,有望获得新的杀虫基因.
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