New combinations of cry genes from Bacillus thuringiensis strains isolated from northwestern Mexico

Twenty eight Bacillus thuringiensis strains isolated from the Tijuana-Ensenada region of northwestern Mexico were analyzed to determine the distribution of cry and cyt genes. Crystal production by the strains was examined by scanning electron microscopy, which showed the predominance of cubic crystals. Alkaline-dissolved and trypsin activated crystals were also analyzed by SDS-PAGE, yielding bands of 40-200 kDa. The cry1 and cry2 genes were molecularly characterized using general and newly designed specific primers in addition to other oligonucleotides (cry3, cry4, cry8, cry9, cry11, Nem, cry25, cry29 and cyt), resulting in the identification of novel gene combinations. The use of specific primers for cry1A, cry1B, cry1C, cry1D, cry1E, cry1F and cry2Aa, cry2Ab, cry2Ac, cry2Ad showed differences in the distribution of cry1 (36%), cry2 (71%), and cyt (40%) in strains from Tijuana-Ensenada compared to other previously studied regions. Bioassays were conducted on Manduca sexta larvae to analyze the Cry insecticidal capacity of the isolated strains. The hemolytic activity of the Cyt toxin from the same strains was assessed in human erythrocytes.