Novel fermentation media for production of δ-endotoxins from Bacillus thuringiensis

Abstract

Novel approaches were pursued in the development of practical media for δ-endotoxin production by Bacillus thuringiensis subspp. kurstaki and entomocidus. Several agro-industrial by-products, including cottonseed meal, fish meal, beef blood, slaughterhouse residues, corn steep liquor, and sorter liquor, were investigated for their abilities to support toxin production by these varieties. In addition, fodder yeasts and a variety of low-priced plant proteins available in Egypt, exemplified by such leguminous seeds as horse beans, kidney beans, lima beans, soybeans, chick peas, lentils, and peanuts were incorporated in fermentation media as sole sources of proteins for biosynthesis of the endotoxins. The cotton pests, Spodoptera littoralis, Spodoptera exigua, and Heliothis armigera, were used as test insects for biological assays of spore-δ-endotoxin formulations derived from the novel fermentation media. Fodder yeast, beef blood, and slaughterhouse residues were among the by-products yielding good sporulation titers and potent spore-δ-endotoxin preparations. Formulations of subsp. kurstaki produced from media containing these nutrients killed 80–100% of larvae of H. armigera when tested at 500 μg/ml diet. Most of the formulations derived from fermentations using leguminous seeds as sole sources of protein also contained high levels of spores and endotoxin. For example, LC 50 values determined against S. littoralis of spore-endotoxin preparations of subsp. entomocidus grown in media containing kidney beans, chick peas, or peanuts were 93.4, 93.4, and 110.0 μg/ml diet, respectively. The application of these findings to the practical use of B. thuringiensis is discussed.