Molecular characterization of Bacillus thuringiensis strains from Argentina

Bacillus thuringiensis INTA 7- 3, INTA 51-3, INTA Mo9-5 and INTA Mo14-4 strains were obtained from Argentina and characterized by determination of serotype, toxicity, plasmid composition, insecticidal gene content (cry and vip) and the cloning of the single-vip3A gene of the INTA Mo9-5 strain. The serotype analysis identified the serovars tohokuensis and darmstadiensis for the INTA 51-3 and INTA Mo14- 4 strains, respectively, whereas the INTA Mo9-5 strain was classified as autoagglutinated. In contrast to the plasmid patterns of INTA 7- 3, INTA 51-3 and INTAMo9-5 (which were similar to B. thuringiensis HD-1 strain), strain INTA Mo14- 4 showed a unique plasmid array. PCR analysis of the four strains revealed the presence of cry genes and vip3A genes. Interestingly, it was found that B. thuringiensis 4Q7 strain, which is a plasmid cured strain, contained vip3A genes indicating the presence of these insecticidal genes in the chromosome. Bioassays towards various lepidopteran species revealed that B. thuringiensis INTA Mo9-5 and INTA 7- 3 strains were highly active. In particular, the mean LC50 obtained against A. gemmatalis larvae with the INTA Mo9-5 and INTA 7- 3 strains were 7 (5.7 - 8.6) and 6.7 (5.6-8.0) ppm, respectively. The INTA Mo14- 4 strain was non-toxic and strain INTA 51-3 showed only a weak larvicidal activity.