Nutritional requirements of a strain of Bacillus thuringiensis subsp. kurstaki and use of gruel hydro for the formulation of a new medium for δ-endotoxin production

Nutritional requirements of a strain of Bacillus thuringiensis (Bt) subsp. kurstaki were elucidated for delta-endotoxin production. The effect of some principal nutrients was deeply investigated, showing several nutritional and metabolite limitations in Bt growth and delta-endotoxin synthesis. This led us to formulate a new medium based on the hydrolysate of gruel, a cheap and abundant byproduct of semolina factories, supporting growth and delta-endotoxin synthesis. After hydrolysis of gruel by alpha-amylase, followed by proteolysis using alcalase, the resultant soluble material substituted glucose very well for Bt delta-endotoxin production. Indeed, 15 g/L total sugars coming from that hydrolysate, supplemented by 5.4 g/L ammonium sulfate as nitrogen source and either 5 g/L yeast extract or 3 g/L peptone from casein or 3 g/L casaminoacids or 0.25 g/L cysteine or aspartic acid, were the principal components of this new medium in which almost 1 g/L of delta-endotoxin in 4.5 g/L total dry biomass was produced.