Isolation and characterization of a new Bacillus thuringiensis strain with a promising toxicity against Lepidopteran...

Insecticides derived from Bacillus thuringiensis are gaining worldwide importance as environmentally desirable alternatives to chemicals for the control of pests in public health and agriculture. Isolation and characterization of new strains with higher and broader spectrum of activity is an ever growing field. In the present work, a novel Tunisian B. thuringiensis isolate named BLB459 was characterized and electrophoresis assay showed that among a collection of 200 B. thuringiensis strains, the plasmid profile of BLB459 was distinctive. SmaI-PFGE typing confirmed the uniqueness of the DNA pattern of this strain, compared with BUPM95 and HD1 reference strains. PCR and sequencing assays revealed that BLB459 harbored three cry genes (cry30, cry40 and cry54) corresponding to the obtained molecular sizes in the protein pattern. Interestingly, PCR-RFLP assay demonstrated the originality of the BLB459 cry30-type gene compared to the other published cry30 genes. Insecticidal bioassays showed that BLB459 spore-crystal suspension was highly toxic to both Ephestia kuehniella and Spodoptera littoralis with LC50 values of about 64 (53-75) and 80 (69-91) μg of toxin cm(-2), respectively, comparing with that of the commercial strain HD1 used as reference. Important histopathological effects of BLB459 δ-endotoxins on the two tested larvae midguts were detected, traduced by the vacuolization of the apical cells, the damage of microvilli, and the disruption of epithelial cells. These results proved that BLB459 strain could be of a great interest for lepidopteran biocontrol.