The 20-kDa protein of Bacillus thuringiensis subsp. israelensis enhances Bacillus sphaericus 2362 bin toxin synthesis.

Improving the amount of protein endotoxins synthesized by Bacillus thuringiensis and B. sphaericus per unit of culture medium is important because higher yields typically correlate with higher insecticidal activity per unit weight of spore/toxin mixtures. Higher levels of synthesis can also result in larger crystals that could persist for longer periods in the environment. Improving endotoxin production in B. thuringiensis can be achieved by manipulating genetic elements that regulate protein synthesis at the transcriptional, translational, and even posttranslational levels. In the present study, we used a combination of genetic elements to improve yields of B. sphaericus 2362 binary toxin (Bin) in B. thuringiensis. Our results show that a 20-kDa chaperone-like protein, which occurs as the third open-reading frame in the cry11Aa operon, improves Bin yields when expression of the genes encoding this binary toxin is driven by the native bin promoter, cyt1A promoters, or a novel cyt1A-p/STAB-SD expression system, the latter of which yields maximal levels of Bin synthesis. The 20-kDa helper protein increased Bin toxin levels in B. thuringiensis by as much as 53% and concomitant toxicity by at least 90% when Bin was produced using the cyt1A promoters.