Purification of the parasporal crystals ofBacillus thuringiensis subsp.israelensis and development of a novel bioassay technique

Summary A spore-free parasporal crystal suspension was prepared fromBacillus thuringiensis subsp.israelensis by an aqueous biphasic separation technique and the waste fractions quantified with regard to spore numbers and insecticidal potencies. The technique proved efficient in selectively removing spores from the spore-crystal mixture. The final crystal suspension was used to develop a novel bioassay system which allowed rapid determination of crystal effectiveness in 1/8 to 1/6 of the time required in the conventional mortality versus concentration bioassay.