Isolation Of Bacillus Thuringiensis From Soil Of Tropic Primeval Rain Forest In Hainan Province And Biological Chzaracteristics Of Two Isolated Strains

In this study, a method was developed to isolate Bacillus thuringiensis from soil samples collected from the Jianfengling tropic primeval rain-forest and the Bawangling tropic primeval rain-forest in province of hainan. Thirty-five Bt strains were isolated from 532 soil samples and the proportion was 6.58%,there were bipyramidal,square and spherocal crystals.The morphological character of two isolated strains named W015-1 and S1478-1 were tested , the results indicated that both strains were short bacillus, and they could form spores and bipyramidal crystals. The sequence analysis of 16srDNA fragment amplified from total DNA of two strains by PCR showed that W015-1 shared 97% 16srDNA sequence homology with B.thuringensis, and S1478-1 shared 99%. SDS-PAGE electrophoresis indicated the crystal was composed of 130Kda proteins by using B.thuringensis kurstaki HD-73 as controls. PCR-RFLP technology was used to analyse cry-type genes,the results showed W015-1 and S1478-1 contained cry1Ac.The bioassay against Plutella xylostella in vitro showed the isolated strain, S1478-1 was highly toxic. Correction mortality was 100%.LC₅₀ was 6.0×10⁸ spore/ml.