Characterization of locally isolated Bacillus thuringiensis for the Development of Eco-friendly Biopesticides in Bangladesh

Bacillus thuringiensis (Bt) was investigated in three different habitats (vegetable and crops-cultivated soils, phylloplanes and insect guts) of Bangladesh. A total of 61 Bacillus cereus-like isolates were obtained by selective methods and 57 of those were identified as Bacillus thuringiensis isolates based on their hemolytic activity, presence of parasporal crystal proteins, plasmid profile and crystal protein profile. The prevalence of Bt was highest (60%) in soil samples followed by leaf and insects. Five different types of parasporal crystal proteins (spherical, bipyramidal, irregular pointed, cuboidal and irregular shaped) were observed among the isolates which indicates the diversity of the local Bt isolates examined. In addition, confirmation of the strain identification was done using 16S rDNA gene sequencing. Plasmid analysis recovered from the isolates yielded at least one 15kb DNA, which is well comparable to the reference strain, B. thuriginesis kurstaki var. HD-73. Further similarity between the test and standard strains was observed while analyzing crystal proteins on a SDS-polyacrylamide gel that produced major bands of Cry1, Cry2 and Cry9 type proteins. Bioassay performed with isolates Bt-01i, Bt-25f and reference strain, Bt kurstaki var. HD-73 against pulse beetles Callosobrochus chinensis resulted LC₅₀ values of 0.30, 0.72 and 0.22 mg/ml crude proteins respectively which demonstrated their competency in Biopesticide production and application.