Zhang Wenhui, Smith Leonard A, Plantz Bradley A, Schlegel Vicki L, Meagher Michael M
Department of Chemical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68583-0919, USA.
Biotechnol Prog. 2002 Nov-Dec;18(6):1392-9. doi: 10.1021/bp025516w.
The methylotrophic yeast Pichia pastoris is an effective system for recombinant protein productions that utilizes methanol as an inducer, and also as carbon and energy source for a Mut(+) (methanol utilization plus) strain. Pichia fermentation is conducted in a fed-batch mode to obtain a high cell density for a high productivity. An accurate methanol control is required in the methanol fed-batch phase (induction phase) in the fermentation. A simple "on-off" control strategy is inadequate for precise control of methanol concentrations in the fermentor. In this paper we employed a PID (proportional, integral and derivative) control system for the methanol concentration control and designed the PID controller settings on the basis of a Pichia growth model. The closed-loop system was built with four components: PID controller, methanol feed pump, fermentation process, and methanol sensor. First, modeling and transfer functions for all components were derived, followed by frequency response analysis, a powerful method for calculating the optimal PID parameters K(c) (controller gain), tau(I) (controller integral time constant), and tau(D) (controller derivative time constant). Bode stability criteria were used to develop the stability diagram for evaluating the designed settings during the entire methanol fed-batch phase. Fermentations were conducted using four Pichia strains, each expressing a different protein, to verify the control performance with optimal PID settings. The results showed that the methanol concentration matched the set point very well with only small overshoot when the set point was switched, which indicated that a very good control performance was achieved. The method developed in this paper is robust and can serve as a framework for the design of other PID feedback control systems in biological processes.
甲基营养型酵母毕赤酵母是一种用于重组蛋白生产的有效系统，它利用甲醇作为诱导剂，同时也作为Mut(+)（甲醇利用阳性）菌株的碳源和能源。毕赤酵母发酵采用补料分批模式进行，以获得高细胞密度从而实现高生产率。在发酵的甲醇补料分批阶段（诱导阶段），需要精确控制甲醇。简单的“开-关”控制策略不足以精确控制发酵罐中的甲醇浓度。在本文中，我们采用了一种PID（比例、积分和微分）控制系统来控制甲醇浓度，并基于毕赤酵母生长模型设计了PID控制器设置。闭环系统由四个部分组成：PID控制器、甲醇进料泵、发酵过程和甲醇传感器。首先，推导了所有组件的模型和传递函数，随后进行频率响应分析，这是一种计算最优PID参数K(c)（控制器增益）、tau(I)（控制器积分时间常数）和tau(D)（控制器微分时间常数）的有效方法。使用Bode稳定性判据来绘制稳定性图，以评估在整个甲醇补料分批阶段所设计的设置。使用四种毕赤酵母菌株进行发酵，每种菌株表达一种不同的蛋白质，以验证最优PID设置下的控制性能。结果表明，当设定值切换时，甲醇浓度与设定值匹配良好，仅有小的超调，这表明实现了非常好的控制性能。本文所开发的方法具有鲁棒性，可作为生物过程中其他PID反馈控制系统设计的框架。
