Characterization of cry genes in a Mexican Bacillus thuringiensis strain collection

Mexico is located in a transition zone between the Nearctic and Neotropical biogeographical regions and contains a rich and unique biodiversity. A tot al of 496 Bacillus thuringiensis strains were isolated from 503 soil sample s collected from the five macroregions of the country. The characterization of the strain collection provided useful information on the ecological pat terns of distribution of B. thuringiensis and opportunities for the selecti on of strains to develop novel bioinsecticidal products. The analysis of th e strains was based on multiplex PCR with novel general and specific primer s that could detect the cry1, cry3, cry5, cry7, cry8, cry9, cry11, cry12, c ry13, cry14, cry21, and cyt genes. The proteins belonging to the Cry1 and C ry9 groups are toxic for lepidopteran insects. The Cry3, Cry7, and Cry8 pro teins are active against coleopteran insects. The Cry5, Cry12, Cry13, and C ry14 proteins are nematocidal. The Cry11, Cry21, and Cyt proteins are toxic for dipteran insects. Six pairs of general primers are used in this method . Strains for which unique PCR product profiles were obtained with the gene ral primers were further characterized by additional PCRs with specific pri mers. Strains containing cry1 genes were the most abundant in our collectio n (49.5%). Thirty-three different cry1-type profiles were identified. B. th uringiensis strains harboring cry3 genes represented 21.5% of the strains, and 7.9% of the strains contained cry11 and cyt genes, cry7, cry8, and cry9 genes were found in 0.6, 2.4, and 2.6% of the strains, respectively. No st rains carrying cry5, cry12, cry13, cry14, or cry21 genes were found. Finall y, 14% of the strains did not give any PCR product and did not react with a ny polyclonal antisera. Our results indicate the presence of strains that m ay harbor potentially novel Cry proteins as well as strains with combinatio ns of less frequently observed cry genes.