• Journal of Sericultural and Entomological Science
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• v.33 no.2
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• pp.75-81
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• 1991

The study has been carried out to acquire some basic informations about Bacillus thuringiensis for developing the microbial pesticide. Pathogenicity tests on three of B.thuringiensis var. aizawai, kurstaki, and dendrolimus were determined in two species of insects, H. cunea and B. moris. The pathogencity in varieties of B. thuringiensis against H. cunea and B. mori was depended on instar age of tested larvae. Bacillus thuringiensis var. dendrolimus, kurstaki, aizawai are arranged in order of pathogenicity against H. cunea and B. mori. In result Bacillus thuringiensis var. kurstaki was shown the most stable toxicity with respect to each instar of tested larvae.

• The Journal of Natural Sciences
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• v.6 no.1
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• pp.41-48
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• 1993

A cloned delta-endotoxin gene from Bacillus thuringiensis var. kurstaki NRD 6 was mutated at N-terminal toxic portion of the protoxin by site-directed mutagenesis. A Stu 1 restriction site was created in protoxin region of the mutant B.t.kurstaki NRD 6-Stu 1 which changed A to C in 177 region of the protoxin(silent mutation). Antigenic property of crystalline inclusion (delta-endotoxin) of the mutant was no difference to intact strain by the western blot analysis and its toxidity threshold value was also showed 0.015~0.030ng against Choristoneura femiferana-1 insect, similar with 0.01~0.024ng of parent strain, but stronger than that of B.t.kurstaki NRD 5 (500~1000ng) and B.t.kurstaki NRD 4(none toxic).

• Journal of Sericultural and Entomological Science
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• v.34 no.1
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• pp.41-48
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• 1992

Dissolution and degradation of the parasporal crystal proteins produced from B. thuringiensis var. kurstaki, B. thuringiensis var. dendrolimus and B. thuringiensis var. aizawai were investigated. SDS-polyacrylamide gel electrophoresis analysis showed that the crystals contained major protein with molecular weight of approximately 134 kDa for B. thuringiensis var. aizawai 143 kDa for B. thuringiensis var. kurstaki and 149 kDa for B. thuringiensis var. dendrolimus, respectively. Crystals of three other strains were incubated alkali solutions at various pH or gut juice of Silkwarm Bombyx mori, Fall webworm Hyphantria cunea, and Common Cabbage worm Pieris rapae. When crystals of these strains were solubilized by alkali solutions, no major differences among strains B. thuringiensis could be detected. Among the strains studied, crystal protins (130-66 kDa) consist of protease resistant polypeptides in the 45-66 kDa size range when treated with gut juice of three insect species.

• Journal of Sericultural and Entomological Science
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• v.37 no.1
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• pp.62-67
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• 1995

Ultrastructural changes of tissues caused by Bacillus thuringiensis var. kurstaki $\delta$-endotoxin intoxication of Hyphantria cunea were observed by transmission electron microscopy. Bt $\delta$-endotoxin crystals induced the disruption of microvilli, vacuolation of cytoplasm, changes in the cisternae of the endoplasmic reticulum, disappearance of basal striations, loss of ribosomes, and changes in the configurations of mitochondria in the columnar cell of midgut. The fat body cells also showed spherical endoplasmic reticulum and distorted mitochondria, and then the cells were destroyed.

• Journal of Sericultural and Entomological Science
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• v.37 no.1
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• pp.68-73
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• 1995

The toxic effect of Bacillus thuringiensis var, kurstaki $\delta$-endotoxin was determined in the midgut, fat body and Malpighian lobules from larvae of Hyphantria cunea using the au-toradiography and Western blot methods. Bt $\delta$-endotoxin crystals inhibited protein synthesis and elongation factor-2 activity of all tissues tested.

• Microbiology and Biotechnology Letters
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• v.13 no.3
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• pp.315-319
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• 1985

Delta-endotoxin crystals of B. thuringiensis var. kurstari and B. thuringiensis var. israelensis were purified by NaBr density gradient centrifigation and the wet weight of the BTK endotoxin was approximately 23.79％ of the cell wet weight and that of BTI was 25％. The shape of BTK crystal was bipyramidal, whose size was 1.7${\mu}{\textrm}{m}$ $\times$ 0.9${\mu}{\textrm}{m}$ and that of BTI was a spheroid, whose size was about 1.6$\times$0.45${\mu}{\textrm}{m}$. The molecular weight of BTK crystal protein was approximately 134,000 daltons and that of BTI was about 128,000 daltons.

• Journal of Sericultural and Entomological Science
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• v.36 no.2
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• pp.162-167
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• 1994

Surface changes of tissues caused by B. thuringiensis var. kurstaki-$\delta$-endotoxin intoxication of Helicoverpa assulta were observed by scanning electron microscopy. Bt-endotoxin crystals induced the erosion and disruption on the surface of all tissues tested. The results revealed that the toxin binds to all exposed plasma membranes without apparent specificity for particular membrane domains.

• Journal of Sericultural and Entomological Science
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• v.35 no.2
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• pp.120-128
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• 1993

The objective of this study is to identify plasmids of Bacillus thuringiensis var. kurstaki HD-1(B. t k HD-1) toxic to lepidopteran larvae. The results from agarose gel electrophoresis indicated that the bacterium contained 9 plasmids with approximate sizes of 1.4, 4.9, 5.4, 9.3, 10, 29, 44, 52, and 150 megadaltons(Md). By treating the wild type of B. t k HD-1 with either SDS or EtBr as curing agent, 26 cured mutants of the bacterium were obtained, 9 of them were crystallifereous(cry+) and the others acrystallifereous(cry-). Plasmids from B. t k HD-1 were transferred to B. cereus 569 strR cry- recipients(Bc569 M1). Among 13 isolates of Bc569 M1 transcipient, 11 of them were capable of producing the crystal toxic proteins. The plasmid patterns of Bc569 M1 transcipients and partially curved mutants of B. t k HD-1 on agarose gel electrophoresis suggested that the 29 and 44Md plasmids should be involved in the production of crystalline toxic proteins.

• Journal of Sericultural and Entomological Science
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• v.28 no.1
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• pp.43-53
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• 1986

Among many microbial pesticides, Bacillus thuringiensis is one of the most hopeful pesticide and some commercial products have been appearing on the market. Because these commercial products contain living spores and toxins of the organism, there is a danger that living spores of B. thuringiensis may be scattered by wind and cause a great damage in the sericulture areas. In order to avoide these risks it is desirable to select the strain which has low pathogenicity to the silkworm, and at the sometime being highly pathogenic to the pest insects. Thus this study has been carried out to acquire some basic informations about the procedure of desicable strain selection. Three strains of B. thuringiensis var. kurstaki, var. dendrolimus and var. aizawai were used for the pathogenicity test on the silkworm, Bombux mori and the fall webwarm, Hyphantria cunea. Those strains were investigated by the agarose gel electrophoresis patterns of plasmid DNA determine whether mutation had occured. Pathogenicity tests were carried out of using isolated crystal proteins and spore-crystal protein to mixtures of each strain, seperatively. In case of using spore-crystal protein mixture, the order of pathogenicity in varities of B. thuringiensis against B.mopri and H.cunea were kurstaki, aizawai, dendrolimus and kurstaki, dendrolimus, aizawai, respectively. But using isolated crystal proteins, dendrolimus had the highest toxicity to H. cunea and the lowest toxicity to B. mori among tested three strains. From the above results, dendrolimus was presumed the most desirable straing for using microbial pesticide.

• Proceedings of the Zoological Society Korea Conference
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• 1994.10a
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• pp.264-264
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• 1994