Bt W015-1, A <i>Bacillus thuringiensis</i> Strain from Diseased Larva of Silkworm with Highly Larvacidal Toxicity against Lepidopteran Insects

Abstract

In 2005, Dr. X. J. Fang’s group from Hainan Institute of Tropical Agricultural Resources (HITAR) isolated a Bacillus thuringiensis isolate (isolate No:20050509W015) from the mid-gut of diseased and dead larva of silkworm ( Bombyx mori ) that were collected from the sericulture farmers of the region of Hangjiahu (Hangzhou, Jiaxing and Huzhou) in Zhejiang province of China. Bt W015-1 was found to produce crystalline protein toxins with high larvicidal effects against Lepedopterans. Scanning electron microscope observation showed that the strain can produce high-yielding bipyramid crystals during sporulation. SDS-PAGE analysis showed that the protein is about 130 kDa in. Furthermore, bioassays conducted on the diamondback moth demonstrated that the strain is highly toxic. The plasmid profile of the Bt W015-1 exhibited in most part no difference in size and band spectrum from model strain HD73 of Btt, but showed striking difference from the HD1 strain of Btt and Bti. The cry genotype is significantly different in cry1Ac restriction cutting sites from the standard strain HD73 of Btt. The cloned gene cry1Ac22 gene (Accession number EU282379), which encodes a protein of 1 178 amino acid residues, and it was ligated into E. coli M15, can express 130 kDa proteins that show high insecticidal activities against lepidopteran diamondback moth ( Plutella xylostella ).