Citation:Zakeel, M.C.M., Dissanayake, D.M.D., & Weerasinghe, P.A.(2009). Molecular characterization of bacillus thuringiensis strains isolated from a selected site in Nochchiyagama, Anuradhapura in Sri Lanka. International Journal of Tropical Agricultural Research & Extension, 12(5), 31-34.
Date:2009-06-01
Abstract:
The protein toxins produced by Bacillus thuringiensis are the most widely used natural insecticides in
vector and pest control in agriculture. B. thuringiensis strains present in surface and sub-surface soil
samples collected from Nochchiyagama were isolated by 0.25M sodium acetate selection method. Iso lated B. thuringiensis was grown on Luria Bertani agar medium and stained by Gram staining proce dures. Sixty isolates of B. thuringiensis were identified by Coomassie Blue staining procedure and char acterized based on colony morphology, crystal shape, plasmid profile and bioassay. Results revealed
that sub-surface samples had more B. thuringiensis counts than surface soils. This study also indicated
that B. thuringiensis was abundant in soils contaminated with animal wastes. All the isolates formed
‘pan cake’ shape circular colonies with smooth or serrate margins with varying diameter. Fifty five iso lates were found to have rod shape crystals, 4 were spherical shape and only one isolate had rhomboidal
shape crystal. Thirty six isolates were toxic to the third instar larvae of Aedes aegypti including the iso late which contained rhomboidal shape crystal. All the other isolates found toxic to the mosquito larvae
consisted with rod shape crystal inclusion bodies. There were eight different B. thuringiensis strains
among the isolates and 55% of these were B. thuringiensis israelensis.
