Improvement of Bacillus thuringiensis bioinsecticide production by sporeless and sporulating strains using response surface methodology
Saoussen Ben Khedher, Amel Kamoun, Samir Jaoua, Nabil Zouari
Laboratoire de Protection et Amélioration des Plantes (Equipe Biopesticides), Center of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
Statistical experimental designs, involving a Plackett–Burman design followed by a rotatable central composite design were used to optimize the culture medium constituents for Bacillus thuringiensis bioinsecticide production. This was carried out by using firstly an asporogenic strain and extrapolated to some sporeless and sporulating strains. Initial screening of production parameters was performed and the variables with statistically significant effects on delta-endotoxin production were identified: glucose, glycerol, yeast extract and MnSO4. These variables were selected for further optimization by response surface methodology. The obtained results revealed that the optimum culture medium for delta-endotoxin production consists of 22.5 g/l of glucose, 4.8 g/l of glycerol, 5.8 g/l of yeast extract and 0.008 g/l of MnSO4. Under these conditions, delta-endotoxin production was 2130 and 2260 mg/l into 250 and 1000 ml flask respectively, which represent more than 38% improvement in toxin production over the basal medium (1636 mg/l). Such medium composition was shown to be suitable for overproducing delta-endotoxins by sporeless and sporulating strains.