INCREASED TOXICITY OF MODIFIED MOSQUITOCIDAL BINARY TOXINS OF BACILLUS-SPHAERICUS EXPRESSED IN ESCHERICHIA-COLI

The binary mosquitocidal genes of 51-kDa and 42-kDa proteins isolated from Bacillus sphaericus 1593 have been expressed at moderate levels i n Escherichia coli employing the pQE expression system. The expressed proteins are readily visible in Coomassie-blue-stained protein gels. T he recombinant E. coli cells expressing toxic proteins mere toxic towa rds Culex larvae. During the assembly of crystals in B. sphaericus, th e 42-kDa toxin is first cleaved at the N-terminal end by a specific B. sphaericus protease. To express the toxins in E. coil the B. sphaeric us specific protease-recognition site was deleted at the N-terminal en d of the 42-kDa toxin, thereby mimicking the structure of the toxin as present in the crystal. This modification resulted in a twofold incre ase in the toxicity of the E. coli cells expressing the modified 42-kD a toxin as a constituent of the binary toxin. Our results demonstrate the utility of this modification for heterologous expression of the bi nary toxin genes from B. sphaericus.