NUTRITIONAL-REQUIREMENTS OF A STRAIN OF BACILLUS-THURINGIENSIS SUBSP KURSTAKI AND USE OF GRUEL HYDRO FOR THE FORMULATION OF A NEW MEDIUM FOR DELTA-ENDOTOXIN PRODUCTION

Nutritional requirements of a strain of Bacillus thuringiensis (Bt) su bsp. kurstaki were elucidated for delta-endotoxin production. The effe ct of some principal nutrients was deeply investigated, showing severa l nutritional and metabolite limitations in Bt growth and delta-endoto xin synthesis. This led us to formulate a new medium based on the hydr olysate 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 r esultant soluble material substituted glucose very well for Bt delta-e ndotoxin production. Indeed, 15 g/L total sugars coming from that hydr olysate, supplemented by 5.4 g/L ammonium sulfate as nitrogen source a nd either 5 g/L yeast extract or 3 g/L peptone from casein or 3 g/L ca saminoacids 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.