Nutritional Requirements to Improve Delta-Endotoxins Production of Bacillus thuringiensis var. kurstaki Using Mixed Designs Modelling

Abstract

Bacillus thuringiensis kurstaki is a soil bacterium that produces insecticidal toxins called delta-endotoxins. In order to increase the toxic crystal concentrations in a low-cost culture medium and thus improve the biopesticide quality to control insect pests, the Plackett–Burman screening method was applied. It was shown a tool to evaluate the significance of the selected seven factors (KH2PO4, K2HPO4, MgSO4, MnSO4, FeSO4, soybean meal, starch) which are necessary to the production of the delta-endotoxins. This was performed into two different shake flasks (250 and 500 ml). The main factors that affected the production of delta-endotoxins are shown to be soybean meal, starch, and FeSO4 in 250 ml culture flasks. In 500 ml culture flasks, soybean meal and FeSO4 are the principal factors influencing the delta-endotoxin production. The multiple linear regression, a method applied as the merging dataset of the two Plackett–Burman designs, established that soybean meal and starch are the factors positively affecting the production of delta-endotoxins, in contrast to FeSO4. Furthermore, the available oxygen in culture flasks showed no significant negative effect on delta-endotoxin production. This study revealed that mixed method designs were useful to identify the significance and the effect of hidden culture parameters.