Abstract
Abstract Bioinsecticide is one of the important products of bioindustries. In Taiwan, the government is promoting. The bioinsecticides derived from Bacillus thuringiensis have been globally used. Thuringiensin which is heat-stable with broadly insecticidal activity is produced by Bacillus thuringiensis subsp. darmstadiensis, HD-199, in this study. Thuringiensin can improve the insecticidal activity of the traditional biocontrol agent derived fromδ-endotoxin. So it have highly commercial potential. Scale-up of the fermentor makes the commercialization come true. Understanding the dynamics of the fermentation system can contribute a satisfactory scale-up. In this study, mixing, which is an important factor in large-scale fermentor, is investigated in the laboratory scale fermentor. In the laboratory scale fermentor, which is well mixed, the technique of pH block pulse and pH periodic variation is employed. The change of pH value simulates poor mixing in a large-scale fermentor. We found that the variations of pH did not have effects on the production of product during the stationary phase, but significantly affected both the growth of microbes and the production of thuringiensin during the exponential phase. Similarly, we introduced the block pulse and step change of agitation and aeration to investigate the problem of oxygen transfer and the effect of shear stress. The oxygen transfer played an important role during the exponential phase. It limited the growth of the microbes and reduced the production of thuringiensin, if the oxygen was not sufficiently provided. The yield could be improved by reducing the agitation rate during the stationary phase.