Exchange of domain I from Bacillus thuringiensis Cry1 toxins influences protoxin stability and crystal formation

Influence of domain I exchange on the stability and production of Bacillus thuringiensis Cry1 protoxins as well as on the shape of inclusion and toxic ity to Spodoptera exigua and Plutella xylostella larvae was investigated. C himeric genes were prepared by exchanging the regions coding for domain I b etween Cry1Aa, Cry1Ab, Cry1Ac, Cry1C, and Cry1E. The AcCC chimera accumulat ed into bipyramidal inclusion bodies, whereas CEE produced round-shaped inc lusion bodies, and ECC and AaEE protoxins produced small granules. AbEE and EAaAa did not produce any inclusion body and were visualized by immunodete ction only. AcCC, GEE, ECC, and AaEE were stable to trypsin, whereas AbEE a nd EAaAa were not. Bioassays showed that the chimeras were not toxic in viv o. However, S. exigua larvae fed with the activated AcCC toxin displayed a lower growth rate.