Optimization of mosquitocidal toxin synthesis from Bacillus sphaericus using gene fusions.

β-Galactosidase gene fusions have been used to monitor the progress of mosquito-larvicidal-toxin gene expression in Bacillus sphaericus strain 2362. β-Galactosidase estimation in cells from late-growth-phase batch cultures was compared with larvicidal toxicity after incubation for 48 h. Conditions which promoted efficient sporulation, such as plentiful trace elements and relatively crude protein sources (soybean or cottonseed flours), enhanced reporter gene expression and provided high toxicity. However, acetate, which repressed sporulation, similarly repressed binary toxin yield. Gene fusions to the binary and 100-kDa toxin genes of B. sphaericus could be useful for the rapid screening of fermentation conditions for the local production of this larvicidal bacterium but, in view of the poor correlation with toxicity at high toxicity levels, such experiments should be confirmed with bioassays.