| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 90 === Abstract
The motility of bacteria is a mechanism in response to the environment change and the growth of the cells. In this, a parameter, called “motile intensity”, for determining the motility of a bacterium is defined. The motile intensity is defined as the mean specific kinetic energy of the cells. In addition, the relationships among the growth of B. thuringiensis, the production of thuringiensin, and the motile intensity of the cells are investigated. Finally, an economical process of fermentation based on the motile intensity is developed.
In chapter 3, the first stage of the experiments, 7 kinds of bacteria and use two parameters, “motile intensity” and “mean swimming speed”, to characterize the motility of bacteria are observed. The results reveal that the motile intensity is an appropriate parameter for describe the motility of the cells. A rapid increase in motile intensity during the lag phase, with a peak between the post-lag phase and the early exponential phase is also observed. In addition, it is found that the specific glucose consumption rate of the cells exhibits the same curve as the motile intensity on cultivation.
In chapter 4, the second stage of the experiments, it is found that the motile intensity can be an indicator for the activity of the cell growth. If the environmental variables change at a stage where the motile intensity is at high level, the cells will get more damage for the thuringiensin production. In addition, the motile intensity commonly decreases during cultivation. The reason is that B. thuringiensis produces some compounds to inhibit the flux of the TCA cycle on cultivation. Most energy is consumed to keep the growth of the cells. So there is no enough energy left for the motility of the cells. Moreover, it is found that the maximum motile intensity of the cells exhibits a matching with the productivity of thuringiensin in an almost linear way.
In chapter 5, the finally stage of the experiments, a new process of fermentation based on the motile intensity for cultivation is developed. This process includes the following factors: optimum inoculum time decision, droplet medium selection, and the design of a suitable fed-batch strategy. The time that the motile intensity of the cells is at the maximum magnitude on cultivation is the optimum inoculum time. In addition, a new medium design method, called “droplet medium selection”, is developed. An optimum medium composition and the environmental conditions can be found very quickly by means of the droplet medium selection. Finally, a simple strategy for fed-batch cultivation is proposed. The strategy consists of two steps: (i) initiate the feeding at the maximum magnitude of the motile intensity of B. thuringiensis with an optimum substrate concentration control; (ii) terminate the feeding at low motile intensity (or non-motile) of the cells.
In summary, the motility of the Bacillus thuringiensis during cultivation is investigated, and the “motile intensity” for describing the motility is defined. Besides, an appropriate fermentation process is developed. The motile intensity can not only describe the motility of the cells, but also be an indicator for determining the activity of the cells on cultivation.
|
|---|
