In this study, the growth property of Bacillus thuringiensis subsp. thompsoni and the effect of medium composition and growth condition on production of δ-endotoxin was examined.
Bacillus thuringiensis subsp. thompsoni has a not definetely divided, long morphology during growth phase and aggregate at the time when some kinds of nutrients used up. The optical density increases when lysis occurs after sporulation. The growth curve is different from that of other strains because of the aggregation.
The crystal protein production using two different carbon sources, glucose and starch were similiar. Cells require less yeast extract when the carbon source used was glucose compared with starch. However the several benefits of using starch include low price and stability to heat. And yeast extract must be also replaced with other nitrogen source for industrial production.
The effects of varying yeast extract concentration in the media containing starch of 2, 5 or 10g/L were examined in flask cultures. The optimum ratio of starch to yeast extract varied with the starch concentraion since culture condition that supported such as oxygen supply was different in each case. The yeast extract concentration maximum protein production in the midium containing 5 or 10g/L of starch was 2g/L when starch was nearly consumed, cell did not show further. It was found that the nutrients left play an important role in making spores and crystal proteins.
In bioreactor the time period required for sporulation was shorter than that in flask culture, and cells grew again when the media containing 5g/L starch and 2g/L yeast extract was used. Therefore yeast extract concentration that allows efficient utilization of nutrients was newly determined in the fermentor. For the media containing 5g/L and 10g/L starch, the concentration of 3g/L and 5g/L yeast extract, respectively, was found to be effective.
The effect of dissolved oxygen was examined by controlling the DO above 20% in the media containing 10g/L starch and 5g/L yeast extract. The maximum DCW and the protein concentration was lower than those of the DO not controlled case. When the fermentation was carried out in the media containing 10g/L starch and 4g/L yeast extract, the agitation speed of 300rpm allowed higher protein concentration than 400rpm. The different optimum DO exists for different growth conditions.
