Respective role of the 42- and 51-kDa components of the Bacillus sphaericus toxin overexpressed in Bacillus thuringiensis

The 42- and 51-kDa protein genes of Bacillus sphaericus 1593 have been subcloned independently downstream from the cytA gene promoter of Bacillus thuringiensis serovar israelensis and introduced into a non-mosquitocidal strain of Bacillus thuringiensis. Consequently, each protein was overproduced and accumulated as inclusion bodies which were purified. For the first time, the 42-kDa protein inclusions alone were found to be toxic to Culex pipiens larvae (LC50 at 48 h 300 ng ml−1); in contrast, the 51-kDa protein inclusions were not. Moreover, a synergistic effect between these two components was observed.