Optimization of a culture medium based on forage palm for δ-endotoxin production

An alternative culture medium based on forage palm (Cactaceae) and inexpensive nitrogen sources for delta-endotoxin production by Bacillus thuringiensis var. berliner (Btb) was optimized using response surface methodology and the influence of the nitrogen sources on biological activity and morphological properties of the delta-endotoxin has been studied. Effects of forage palm extract concentration (15-25%), ammonium sulphate (0-1 g/L), ammonium chloride (0-1 g/L) and urea concentrations (0-1 g/L) on delta-endotoxin production were studied by a 2(4) full factorial design and optimized by a 2(2) central composite design (CCD). Statistical analysis showed that forage palm and ammonium sulphate were the main factors to enhance delta-endotoxin production. Different nitrogen sources influenced on biological activity and morphology of crystals. Culture medium constituted by forage palm extract and ammonium sulphate increased delta-endotoxins production in the form of bipyramidal crystals and was more toxic to Spodoptera frugiperda. Forage palm extract and ammonium sulphate were considered to optimization of delta-endotoxin production. Maximum delta-endotoxin production (356 mg/L) took place at 30.7% (w/v) of forage palm extract concentration and 1.016 g/L of ammonium sulphate.