Transformation of Bacillus thuringiensis by electroporation

Plasmids were transformed by electroporation into various strains of Bacillus thuringiensis with frequencies of up to 105 transformants/µg. pC 194 transformed all strains tested at a high frequency and cells could be stably transformed with pC194 and pUB110 simultaneously by electroporation with a frequency of 102 pC194 + pUB110 transformant/µg DNA. Low transformation frequencies observed with some plasmids, especially those grown initially in Escherichia coli, could be increased by passage through B. thuringiensis, B. thuringiensis var. israelensis and an acrystalliferous mutant of the same strain transformed at frequencies of 104–105/µg DNA with most of the plasmids tested. A cloned israelensis 27-kDa δ-endotoxin gene was introduced into the israelensis acrystalliferous mutant and a kurstaki acrystalliferous mutant by electroporation. Both transformants were shown to express the endotoxin gene and to be toxic to Aedes aegypti larvae.