Forced Periodic and Chaotic Control of a Mixed Culture for Efficdient PHB Production

建立了混合培养的非结构化数学模型，其中一种微生物产生的代谢物被另一种微生物同化。为此，我们特别采用了这样的模型系统，即葡萄糖等糖由德布鲁克氏乳杆菌转化为乳酸，乳酸在一个发酵罐中由富营养化Ralstonia eutropha转化为聚β -羟基丁酸盐（PHB）。对每种微生物在不同溶解氧（DO）浓度下进行了分批培养和补料分批培养实验。然后将这些实验数据拟合到可以描述混合培养动力学的数学模型中。部分模型参数表示为DO浓度的函数，部分模型参数根据混合培养实验进行调整。该模型描述了不同浓度的葡萄糖、乳酸、DO和NH_3对微生物、葡萄糖、乳酸和PHB的动态行为的影响。然后利用所建立的模型对最佳工况进行了研究。发现DO浓度的周期性变化提高了PHB产率等性能，并通过实验进行了验证。混沌方式改变DO浓度对性能提高的影响目前尚不清楚，因为目前以这种方式进行的实验很少。这是下一个要探讨的主题。

The unstructured mathematical model was developed for the mixed culture, where the metabolites produced by one microorganism is assimilated by the other microorganism.. For this, we specifically employed such model system that sugars such as glucose were converted to lactate by Lactobacillus delbrueckii and the lactate was converted in turn to poly β -hydroxybutyrate(PHB) by Ralstonia eutropha in one fermentor. Several batch and fed-batch culture experiments were conducted using each microorganism at different dissolved oxygen (DO) concentrations. Those experimental data were then fitted to the mathematical model, which can describe the dynamics of a mixed culture. Some of the model parameters were expressed as functions of DO concentrations, and some of the other model parameters were tuned based on the mixed culture experiments. The model developed describes the effects of such concentrations of glucose, lactate, DO, and NH_3 on the dynamic behavior of such concentrations as both microorganisms, glucose, lactate, and PHB. Optimal operating condition was then investigated using the model developed.It was found that the periodic change in DO concentration improved such performance as PHB yield, and it was verified by experiments. The effect of changing the DO concentration in chaotic manner on the performance improvement is not clear at this stage since very few experiments were conducted so far in this manner. This is the next topic to be pursued.