Correlation of the insecticidal activity of the Bacillus thuringiensis A4 strain against Bactrocera oleae (Diptera) with the 140-kDa crystal polypeptide

The crystals of the soil-isolated Bacillus thuringiensis (Bt) strain A4 con sist of two polypeptides with molecular mass of 140 kDa and 32 kDa that exh ibit insecticidal activity against adult flies of Bactrocera oleae (Diptera ). Plasmid curing applied to this strain resulted in the isolation of sever al subclones exhibiting alterations in their crystal polypeptides as well a s two acrystalliferous subclones. The crystals of subclone 1.1 lacked the 3 2-kDa polypeptide and consisted uniquely of a 140-kDa polypeptide antigenic ally related to the parental 140-kDa crystal polypeptide. Additionally, the crystals of this subclone exhibited insecticidal activity against B. oleae equivalent to that of the parental strain. Therefore, the 32-kDa crystal p olypeptide is dispensable for insecticidal activity, which appears to be de pendent on the presence of the 140-kDa crystal polypeptide.