PCR Detection of cry Genes in Local Bacillus Thuringiensis Isolates

Twelve local B. thuringiensis strains are used in the study, which previously isolated from the soil of seven governorates and characterized by their high toxicity against 2 instars larvae of cotton nd leafworm (Spodoptera littoralis). The PCR amplification analysis of the 12 Bt isolates revealed the presence of amplified fragments characteristic of five different cry genes. Results showed the expected sizes of PCR products of cry1Aa, cry1Ac, cry1I, cry2 and cry3 genes ranging from 2595 to 2985, 209 to 447, 275 to 463, 2028 to 2471 and 1933 to 2130 bp, respectively. Out of the six cry genes investigated, only cry1Ab gene was not found in any of the 12 Bt isolates. Three different Bt. isolates; As-5, As-6 and Ts-7 showed cry1Ac gene only with PCR product size of 238 bp. While, five of the 12 Bt isolates were harboring a combination of different cry genes, such as Gh-3 harbored lepidoptera-active cry1Aa and cry1Ac, lepidoptera-diptera active cry2 gene and coleoptera-active cry3 gene. Two other Bt isolates; Sn-4 and Ts-1 harbored cry1Ac and cry2, while As-2 is containing cry1Aa and cry1Ac. Gh-5 was harbored cry1Aa and cry1I. These profiles of cry genes indicate that Gh-3 isolate was active against lepidopteran, dipteran and coleopteran insects. Four Bt isolates; Qa-6, Qa-7, Fa-8 and Is-1 did not react with any of the six PCR specific cry gene primers. These isolates may have had some other cry genes not identified by the six specific primers used. consequently combined strains are good candidates in the search for biocontrol agents with a wider spectrum of action against many different insects. On the other hand, cry1 genes were the most frequently found among the 12 local Bt isolates and the most common profile of cry1 genes contained cry1Ac and the second abundant genes was cry1Aa and cry2.