In this research, 514 soil samples and dead larvae were collected from Khorassan, Lorestan, Tehran, Ghazvin, East Azarbaijan, West Azarbaijan, Mazandaran and Hamedan Provinces. B. thuringiensis was isolated from the samples using a heat-acetate method and the isolates were identified and classified using biochemical tests. The frequency of B. thuringiensis in soils with different plant communities was studied. According to results, 127 isolates were collected from the samples collected. Most isolates produced atypical and heterogenic and some bipyramidal crystals. Nearly all the isolates were able to hydrolyze starch and gelatin and ferment glucose and fructose, but could not produce indole and H2S or ferment galactose and lactose. The isolates were divided into 8 biochemical types, among which B. thuringiensis subsp. kurstaki was the most frequent type. Total Bt frequency, corresponding to the whole sampling areas, was calculated as being 3.1%; the highest frequency was recorded for Khorassan Province (5.1%) and the lowest for Lorestan Province (0%). No realtionship was found between B. thuringiensis frequency and vegetation status of the soils examined.

Keywords: B. thuringiensis, Biochemical type, Isolation

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