Construction of a Bacillus thuringiensis genetically-engineered strain harbouring the secreted Cry1Ia delta-endotoxin in its crystal

Abstract

Unlike other Bacillus thuringiensis Cry proteins, Cry1 Ia does not form a crystal since it is a secreted delta-endotoxin. We have engineered a Cry1 Iac chimeric protein by substituting the C-terminal part of Cry1 Ia by the corresponding Cry1 Ac part. When expressed in an acrystalliferous B. thuringiensis strain, Cry1Iac did not crystallize, but when expressed in the crystalliferous strain BNS3, the chimeric protein co-crystallized with the endogenous Cry1 A delta-endotoxins forming a typical bipyramidal crystal. The integration of Cry1 Ia in the composition of the crystal of BNS3 led to an increase of its delta-endotoxin production (13%) and to an improvement (60%) of its toxicity against Agrotis ipsilon.