Protein profile diversity of Bacillus thuringiensis strains isolated from lepidopteran larvae

Abstract

Bacillus thuringiensis (Bt) is an aerobic, gram positive, spore-forming, facultative bacteria that produces parasporal crystals containing one or more insecticidal crystal (Cry) proteins, which are selectively toxic to insects and widely distributed in the environment. In spite of the variability of Cry proteins and the range of susceptible organisms, a significant number of insects that cause great losses on crop production are not sensitive to the commercially available Bt toxins. In the present study seven Bt strains isolated from lepidopteran larvae and one reference Bacillus thuringenesis var. Kurstaki strains HD-1 were used for surface and crystal protein profile through sodium dodecyl sulphate poly acrylamide gel electrophoresis (SDS-PAGE). Protein profile revealed presence of 20 to >245 kDa in pre-solubilized form and 18-110 kDa in solubilized form. Based upon protein profile of pre-solubilized and solubilized form of Bt strains, major proteins are categorized into three main groups viz., groups I (18-60 kDa), group II (65-105 kDa) and group III (110->245 kDa).Variation in the molecular weight of crystal proteins showed the presence of a group of Cry toxins in Bt strains isolated from even same source. Low genetic similarity was observed when different Bt strains were clustered based on protein patterns using UPGMA. However to confirm the insecticidal activity of these native Bt strains, there is a need to examine their bio-activity against different insect groups.