MCM Zakeel*, DMD Dissanayake and PA Weerasinghe
Faculty of Agriculture, Rajarata University of Sri Lanka, Puliyankulama, Anuradhapura
Abstrsact
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.
Key words: Bacillus thuringiensis, Colony shape, Molecular characterization, Parasporal crystal inclusion, Plasmid
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