Multiplex PCR screening to detect cry9 genes in Bacillus thuringiensis strains

An extended PCR method was established to rapidly identify and classify Bacillus thuringiensis strains containing cry (crystal protein) genes toxic to lepidopteran, coleopteran, and dipteran pests (Ben-Dov et al., Appl. Environ. Microbiol. 63:4883-4890, 1997). To optimize identification of all reported cry genes, this methodology needs a complete PCR set of primers. In the study reported here, a set of universal (Un9) and specific primers for multiplex rapid screening for all four known genes from the cry9 group was designed. PCR analyses were performed for cry9 genes on 16 standard strains and 215 field isolates of B. thuringiensis. Among the standard strains, only B. thuringiensis subsp, aizawai HD-133, which harbors cry1 and cry2 genes, was positive with Un9 but negative to all four specific primers for cry9 genes. DNA of 22 field-collected isolates was also found to be positive with Un9. These isolates were classified into three cry9 profiles using specific primers; all of them harbor cry1 and cry2. This newly designed set of primers complements the existing PCR methodology for most currently known cry genes.