OPTIMIZATION OF MOSQUITOCIDAL TOXIN SYNTHESIS FROM BACILLUS-SPHAERICUS USING GENE FUSIONS

beta-Galactosidase gene fusions have been used to monitor the progress of mosquito-larvicidal-toxin gene expression in Bacillus sphaericus s train 2362. beta-Galactosidase estimation in cells from late-growth-ph ase batch cultures was compared with larvicidal toxicity after incubat ion for 48 h. Conditions which promoted efficient sporulation, such as plentiful trace elements and relatively crude protein sources (soybea n or cottonseed flours), enhanced reporter gene expression and provide d high toxicity. However, acetate, which repressed sporulation, simila rly repressed binary toxin yield. Gene fusions to the binary and 100-k Da toxin genes of B. sphaericus could be useful for the rapid screenin g of fermentation conditions for the local production of this larvicid al bacterium but, in view of the poor correlation with toxicity at hig h toxicity levels, such experiments should be confirmed with bioassays .