Co-expression of Bacillus thuringiensis Cry4Ba and Cyt2Aa2 in Escherichia coli revealed high synergism against Aedes aegypti and Culex quinquefasciatus larvae

Cry4Ba is a δ-endotoxin produced by Bacillus thuringiensis subsp. israelensis and Cyt2Aa2 is a cytolytic δ-endotoxin produced by B. thuringiensis subsp. darmstadiensis. Cry4Ba produced in Escherichia coli was toxic to Aedes aegypti larvae (LC50 = 140 ng ml−1) but virtually inactive to Culex quinquefasciatus larvae. Cyt2Aa2 expressed in E. coli exhibited moderate activity against A. aegypti and C. quinquefasciatus larvae with LC50 values of 350 and 250 ng ml−1, respectively. Co-expression of both toxins in E. coli dramatically increased toxicity to both A. aegypti andC. quinquefasciatus larvae (LC50 = 7 and 20 ng ml−1, respectively). This is the first report to demonstrate that Cry4Ba and Cyt2Aa2 have high synergistic activity against C. quinquefasciatus larvae.