Abstract
Baculoviruses have been genetically modified to express foreign genes under powerful promoters in order to accelerate their speed of killing. In this study a truncated form of cry1Ab gene derived from
Bacillus thuringinsis
(Bt) subsp.
aegypti
isolate Bt7 was engineered into the genome of the baculovirus
Autographa californica
multiple nuclearpolyhedrosis wild type virus, in place of the polyhedrin gene by using homologous recombination in
Spodoptera frugiperda
(Sf) cells between a transfer vector carrying the Bt gene and the wild type virus linearized DNA. Recombinant wild type virus containing the cry1Ab gene was detected as blue occlusion-negative plaques in monolayers of Sf cells grown in the presence of X-Gal. In Sf cells infected with plaque-purified recombinant virus, the cry1Ab gene was expressed to yield a protein of approximately 82-kDa, as determined by immunoblot analysis. The toxicity of the recombinant virus expressing the insecticidal crystal protein (ICP) was compared to that of the wild-type virus. Infected-cell extract was toxic to cotton leaf worm
Spodoptera littoralis
second instar larvae and the estimated LC
50
was 1.7 μg/ml for the recombinant virus compared with that of wild-type virus which was 10 μg/ml.