Isolation, characterization and screening of Bacillus thuringiensis isolates for lepidopteran toxic cry genes

Abstract

A biorational pesticide, B. thuringiensis (Bt) is a gram positive, spore forming soil bacterium and used as an alternative of chemical insecticides due to the ill effects of synthetic insecticides. B. thuringiensis produce crystal proteins during sporulation stage of its growth cycle and it has insecticidal activity against many insect orders viz., Lepidoptera, Coleoptera, Diptera, Mallophaga, Hymenoptera and Homoptera. Among these cry genes, cry1, cry2, cry9 genes are having specific insecticidal activity against lepidopteran insects. The aim of the present study is to isolate and characterize B. thuringiensis strains based on morpholological and biochemical characters and screening of lepidopteran toxic cry genes. Nineteen strains were obtained from 50 soil samples. Bt index of total B. thuringiensis is 0.49%. Three types of crystals i.e., bipyramidal, cuboidal, spherical shape of crystals and spores attached with crystals were present in isolated B. thuringiensis strains. PCR analysis with specific primers resulted in the amplification of cry1 in 7 isolates, cry2Aa in 15 isolates and cry2Ab in 17 isolates and 4 isolates had combination of three genes viz., cry1, cry2Aa, cry2Ab.