Characterization of Lepidoptera-active cry and vip genes in Iranian Bacillus thuringiensis strain collection

Abstract

The characterization of 70 Bacillus thuringiensis ( Bt) strains isolated from different agro-ecological regions of Iran is presented. Characterization was based on PCR analysis using 25 general and specific primers for cry1, cry2, cry9 and vip3Aa genes encoding proteins active against Lepidoptera, crystal morphology, plasmid profiles, and protein band patterns as well as their insecticidal activity on Heliotis armigera. Isolates containing vip3 Aa gene were the most abundant (82.6%) followed by those containing cry2 (56.5%), cry1 (49%) and cry9 (30%). Twenty-two distinct cry1-type profiles were identified from only cry1-harboring isolates when these were analyzed with specific primers. Several of them were found to be different from all previously published profiles. Finally 7.24% of the isolates did not produce any PCR product. Some strains were positive by universal primers but negative by specific primers for all known genes of cry1, cry2 and cry9 or gave PCR products of different sizes when assayed with cry1C, cry1E, cry1J, cry9A, and vip3a specific primers. These strains may contain a new gene or genes that seem promising for biological control of insects and management of resistance. Based on morphological and molecular studies, 20 potentially Lepidopteran-specific active isolates were selected for bioassays. Four strains showed similar or higher activity against H. armigera larvae than Bt subsp. kurstaki ( Btk) and displayed high similarities with the Btk used in this study with regard to protein and plasmid profiles and the presence of cry genes. These results are important for directing future exploration of microbial control strategies for control of crop pests in the region.