Isolation and characterization of Bacillus thuringiensis (Ernst Berliner) strains indigenous to agricultural soils of Mali

The objective of this work was to isolate and characterize Bacillus thuringiensis from agricultural and other insect breeding sites in Mali. A hundred soil samples were collected from Bamako district, Segou, Sikasso and Timbuktu regions. B. thuringiensis (Bt) was isolated from the samples using a heat-acetate method and the isolates were identified and classified using morphological and biochemical tests. The frequency of B. thuringiensis in soils was noted. The results showed that, 15 out of the 3111 bacterial isolates were putative Bt. thuringiensis. Most isolates produced parasporal crystals. The average Bt index for all the areas sampled was 5.1%; the highest frequency was recorded for Niono in Segou region (11.7) and the lowest for Bozola in Bamako district (0.5). Contrary the known information on the high content and distribution of B. in soils, the agricultural soils of Mali contain few Bt strains, confirmed by the low Bt index obtained.