Abstract
Background
Bacillus thuringiensis (Bt) produces a group of δ-endotoxin proteins designated as cry toxins. No doubt that Bt isolates are excellent potential candidates for biological control strategies.
Results
The present study showed that 12 Bt strains were isolated and characterized at morphological, biochemical, and molecular levels. All the tested 12 Bt strains were gram-positive, endospore-forming, and possessing typical Bt crystal structures under the scanning electron microscopy (SEM). Universal primers direct and reverse of five pairs were used to detect five Cry-type genes (Cry1, Cry2, Cry3, Cry4, Cry7, and Cry8) by the PCR sizes produced from the studied Bt strains. The 16S rRNA PCR technique, 16S gene primer, DNA template, dNTPs, and Taq polymerase produced unique and distinguishable restriction patterns used for the molecular characterization of the studied Bt strains. Based on the PCR products, the frequency of Cry-gene distribution among the tested strains was Cry1 100%, Cry4 85%, and Cry3 62%, and Cry2 and Cry7 frequency was 54%. Based on the activity of insecticidal of the tested Bt strains, Bt1, Bt9, Bt10, and Bt11 were extremely pathogenic; their pathogenicity ranged from 93 to 100% against dipteran and lepidopteran larvae, compared to the other Bt isolates. The nucleotide sequences of amplified 1500 bp conserved region of 16S rRNA genes of four strains blasted using NCBI database compared to NCBI database sequences, and they were reported as native strains of Bt showing high homology with the known Bt strains (99–100%). The nucleotide sequences of Bt1, Bt9, Bt10, and Bt11 were placed in the GenBank database under accession numbers MN860017, MN843958, MN843959, and MN843960, respectively.
Conclusion
The strategies of enhancing the sustainability of crops and vegetables that are targeted by a large number of pathogenic insects require a great effort of exploring novel species and strains of Bt. Herein, native strains of Bt were documented from the eastern province of Saudi Arabia that displayed bio-insecticidal action on larvae of Diptera and Lepidoptera.
Protocol for the fast isolation and identification of insecticidal Bacillus thuringiensis strains from soil
