Morphological and biochemical characterization of four new bacillus thuringiensis strains

Bacillus thuringiensis (Bt), a Gram positive soil bacterium is a well known biocontrol agent. Its pest specific toxicity arises from crystalline inclusion comprising of one or more polypeptides called insecticidal crystal proteins (ICPs) or delta endotoxins produced in the sporulating cells. Any strain of B. thuringiensis may have more than one gene for toxic proteins. Development of B. thuringiensis as a microbial insecticide followed from better strains, increased efficiency in production and quality control lead to the development of formulations with high activity and improved characteristics of sprays. In the present study, four new strains i.e. 1953, 6941, 4714 and 4715 of Bacillus thuringiensis have been taken and characterized using morphological studies, growth curve analysis, different staining methods and several biochemical tests and antibiotic susceptibility test. The four strains showed similar results in some tests as they are all Gram positive, endospore-forming, crystal forming and sporulating at the same interval of growth phase whereas the results of the different biochemical tests like starch hydrolysis test, catalase test, lecithinase production test, fermentation test, esculin hydrolysis test and Voges-Proskauer tests were quite similar among three strains out of the four strains studied. Antibiotic susceptibility test shows that most of the strains were resistant to Ampicillin.