Production of Cry1Ab toxin in E. coli for standardisation of insect bioassays

Standardized bioassays are a prerequisite for any monitoring programme of the effect of transgenic Bt corn on target and non-target insects. A key aspect of these investigations is the quality of Cry1Ab toxin used in the bioassays. In order to provide a uniform quality of Cry1Ab toxin, we expressed and purified the cry1Ab gene in E. coli and analysed the expression product by SDS gel electrophoresis and Western blot. Two forms of Cry1Ab were produced, the Cry1Ab protoxin (~130 kDa) and its trypsinized form (~ 62-67 kDa). Different batches of proteins were produced and tested. In bioassays using the European corn borer (Ostrinia nubilalis) a batch-to-batch difference in the specific activities of different toxin production charges was observed.