Improvement of delta-endotoxin production from local Bacillus thuringiensis Se13 using Taguchi's orthogonal array methodology

Objective: The insecticidal activity of Bacillus thuringiensis directly depends on the yield of delta-endotoxins. In this study, various nutritional and cultural parameters influencing delta-endotoxin synthesis by a local isolate of B. thuringiensis Se13 were investigated using Taguchi methods. Methods: In the first experiment, four factors, incubation period, incubation temperature, initial pH and medium, each at four levels, were selected and an orthogonal array layout of L-16 was carried out. In the second experiment, Taguchi's orthogonal array method of L-27 was used to evaluate the effects of the different concentration of medium components. Taguchi's signal-noise ratio and variance analysis were applied to determine the effect of the factors. After each experiment, verification studies were carried out using determined optimum conditions. Results: The optimum conditions for incubation period, incubation temperature, initial pH, and medium determined as 72 h, 30 degrees C, pH 9, and M4 medium, respectively. In the second experiment, soybean flour (5%), glucose (5%), KH2PO4 (0.3%), K2HPO4 (0.1%), MgSO4 (0.4%) were determined as the optimum conditions. The delta-endotoxin yield was elevated to 1559.25 mu g mL(-1) when the factors were adjusted to optimum level. Conclusion: Optimization using the Taguchi method appeared to be a good choice for the overproduction of delta-endotoxin.