An Efficient Assay of Bacillus thuringiensis Formulations by Low-Vacuum SEM Freeze Drying

摘要

Bacillus thuringiensis (BT) formulations are microbial insecticides commonly used worldwide. Their active ingredients are known to the crystalline delta-endotoxin proteins (IPCs) produced during spore formation. The crystalline proteins are believed to be protoxins, because they are only highly toxic when ingested into susceptible insect midguts.~(1)) The potency of a BT product is determined by the dose-dependent lethal activity of the product as compared to that of an accepted standard BT.~(1)) About 50 years ago, the apearance of the first commercial products based on BT created a need for methods to compared products in various countries. The first protocols were based on spore counts, but because the number of spores does not reflect the amount of crystalline proteins present in the bacteria, this method was unreliable and resulted in some major failures.~(2)) With the development of commercial BT products in France,~(3,4)) a titration method based on cfomparison of the LC_(50)s of a product and standard amterial was developed. This method led to rapid improvements not only in product reliability, but also in increased biological activity of products. The new technique became an instrument for industrial fermentation and formualtion development. In Japan, the silkworm bioassay has been used to determine lepidopteran BT product potency.~(5-7))