Evaluation of Bio-insecticidal Property of Bacillus thuringiensis Strains Isolated from Western Ghats Soil

Abstract

Morphological and cultural characterization of the native twenty isolates obtained from Western Ghats of Kerala, produced creamy white and puffy colonies. The colonies were circular or irregular and flat. Margins were either entire or undulate. Biochemical characterization of native Bacillus thuringiensis (Bt) isolates showed that all the isolates were positive for esculinase and starch hydrolysis tests and gave negative response to gelatin hydrolysis and Voges-Proskauer (VP) test. Shape of crystal proteins were studied in native Bt isolates by staining with Coomassie brilliant blue. The shape of proteins varied from irregular, spherical and composite, but the spherical shape was more common. Of the total of 20 isolates analyzed, 12 isolates produced spherical crystal proteins and 6 isolates produced composite crystal protein. Bioassay of selected four native Bt isolates (Bt-23 Bt-133 Bt-190 Bt-242) and reference strain 4Q1 was done against Drosophila melanogaster. Lethal Concentration (LC50) value was the lowest with the reference strain 4Q1 (6.05 × 108 spores per mL), indicating high level of toxicity. Among the native isolates, Bt-23 recorded the lowest value of LC50 (7.39 × 108 spores per mL). Highest LC50 value of 8.64 × 108 spores per mL was recorded by Bt-242.