Statistical Analysis and Modeling of Sporulation Phase during Fermentation of Bacillus Thuringiensis to Study the Effect of Oxygen and Culture Time on its Bioinsecticide Activity

Due to the importance of Bacillus thuringiensis (Bt) in the biological fight, it is necessary to optimize its fermentation process and decrease its production cost. Statistical analysis is used not only to optimize fermentation conditions but also to describe and predict the culture behavior. In production of biological insecticide, one of the important phases is named as sporulation upon which, this work has been particularly focused on. The oxygen and culture time have an important effect on the production cost. So in the current research, the effect of such factors together with cell concentration, toxicity and sporulation has been considered. Regression analysis of the results, obtained in different conditions of aeration, showed that in all experiments, the percentage of total spores and mature spores increase with time. However, when saturated oxygen is used, this increase shows a very slow trend while in the case of interrupted aeration, the sporulation rate is so fast and the culture reached 100 % mature spore at 44th hours of fermentation. Toxicity and insecticide activity of fermentation product is significant even at the beginning of sporulation phase when time factor has only a positive effect at high oxygen concentrations.