Quantitative determination of δ-endotoxin contents in spray-dried preparations ofBacillus thuringiensis strain GC-91

This report describes a method for quantifying δ-endotoxin contents in spray-dried preparations ofBacillus thuringiensis strain GC-91. δ-Endotoxin is solubilized in the pro-toxin form and separated from other soluble compounds by ion exchange chromatography. The method does not discriminate between the different δ-endotoxins produced by strain GC-91. It is suitable for quality control, since δ-endotoxin concentrations found in different preparations correlate inversely with the LC 50 in bioassays on artificial diet against freshly hatched larvae ofSpodoptera littoralis. A typical batch of spray-dried material contains 1.22%±0.08% δ-endotoxin. The method is most accurate with preparations containing 0.5 to 2.0% toxin, for which triplicate estimations give standard errors close to±0.2%.