Isolation, characterization and molecular identification of Bacillus thuringiensis Alex-13 isolated from Egypt against Spodoptera littoralis

The bacterium Bacillus thuringiensis widely used as bio-pesticide. The specific toxic activity to insects and another microbe(s) regarding the existing of crystals that have different morphologies, sizes, numbers and compositions, as Bt strains the crystals have more different proteins, which contain encoded Cry distinct genes. In this work we isolated 334 colonies from 59 soil samples in 13 local areas in Egypt. Colonies examination was done by microscope for toxin production. During screening, and using biochemical reactions and activity towards S. littoralis, we identified 16 bacterial strains as B. thuringiensis besides Bt wettable powder and standard strain. Only one isolate is the most potent strain, which is also confirmed by molecular characterization. Scanning electron microscopy showed existence of cuboidal crystals in B. thuringiensis Alex-13, and bipyramidal crystals in B. thuringiensis HD-1, a standard strain. Polymerase chain reactions (PCR) revealed existence of Cry1-like sequences beside standard strain, which is confirmed by gel electrophoresis. We also studied the environmental and nutritional conditions requirements (data not show). Which have biological economic importance, therefore, it's necessary for isolation these strains in large scale to reduce using of chemical substances in agriculture field. Bioassay recorded that the highest mortality rates according to results giving of LC50 for 5 days against S. littoralis third instars larvae were 69, 86, and 100(%) in Bt Alex-13, Bt-HD-1 standard strain and Bt commercial wettable powder, respectively.