Isolation and Molecular Identification of Insecticidal Activity Bacillus Thuringiensis Strain Alex-13 Isolated From Different Ecosystems in Egypt against Spodoptera Littolaris
Abstract
The entomopathogenic bacterium Bacillus thuringiensis (Bt) is the most widely used biopesticide. The specific toxic activity to insects and other organisms is related to the presence of crystals that have different morphologies, sizes, numbers and compositions according to the Bt strain. The crystals contain different proteins, which are encoded by distinctCry (crystal) genes. In this work we isolated 334 colonies from 59 soil samples in 13 local area in Egypt, colonies examination has carried out under microscope for toxin production, during screening of these isolates we found 16 bacterial strains has been identified by using biochemical reactions and insecticidal activity against Spodoptera littolaris in addition to Bacillus thuringiensis wettable powder comparable to standard strain, only one isolate which are considered most potent strain were confirmed by molecular characterization. Scanning electron microscopy observed that the presence of cuboidal crystals in Bacillus thuringiensis Alex-13, and observed bipyramidal crystals in case of Bacillus thuringiensis HD-1, as standard strain. Polymerase chain reactions (PCR) revealed the presence of Cry1-like sequences in addition to standard strain, which confirmed by gel electrophoresis. Also, during the studying environmental and nutritional conditions requirements (data not show). Bioassay recorded that the highest mortality rate by determination of LC50 for 5 days against Spodoptera littolaris third instars larvae were 69, 86, and 100(%) in case of Bt Alex-13, Bt-HD-1 standard strain and Bt commercial wettable powder, respectively.
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