The growth of Escherichia coli in fed-batch and continuous culture is examined and resultsshow that a-amylase production is strongly dependent on specific growth rate (dilution rate) of the culture and production is greatest at an intermediate rate. Using continuous culture, it has also been found that the presence of acetate above a certain concentration reduces both ~tmax, and the production of recombinant protein. INTRODUCTIONCulture pH, temperature and dissolved oxygen are among the variables which affect growth and recombinant protein production in Escherichia coli; each is routinely measured and controlled to optimum values. Now that monitoring techniques are more advanced, other variables such as specific growth rate, and the concentrations of nutrient sugars and excreted metabolites can also be controlled. However, before implementing any control strategy, it is important to know what effects these variables might have on a fermentation system.

A computer-based algorithm was used for the open-loop control of specific growth rate in fedbatch cultures of recombinant E.coli.. The control of nutrient feed rate to an exponential trajectory resulted in growth of the culture at a constant specific growth rate. Stable specific growth rates between 0.08 and 0.4 h-1 were achieved.

Many biochemical processes consist of a sequence of operations for which optimal operating conditions (setpoints) have to be determined. If such optimization is performed for each operation separately with respect to objectives defined for each operation individually, overall process performance is likely to be suboptimal. Interactions between unit operations have to be considered, and a unique objective has to be defined for the whole process. This paper shows how a suitable optimization problem can be formulated and solved to obtain the best overall set of operating conditions for a process. A typical enzyme production process has been chosen as an example. In order to arrive at a demonstrative model for the entire sequence of unit operations, it is shown how interaction effects may be accommodated in the models. Optimal operating conditions are then determined subject to a global process objective and are shown to be different from those resulting from optimization of each separate operation. As this strategy may result in an economic benefit, it merits further research into interaction modeling and performance optimization.

This article describes a fully automated system for the on-line monitoring and closed-loop control of a fed-batch fermentation of recombinant Escherichia coli, and presents two case studies of its used in limiting production of unwanted byproducts such as acetic in fed-batch fermentations. The system had two components. The first components, on-line monitoring, comprised an aseptic sampling device, a microcentrifuge, and HPLC System. These instruments removed a Sample from a fermentor, spun it at high speed to separate solid and liquid components, and then automatically injected the supernatant onto an HPLC column for analysis. The second component consisted of control algorithms programmed using the LabView visual programming environment in a control computer that was linked via a remote components were linked so that results from the on-line HPLC were captured and used by the control algorithm was designed to demonstrate coarse feedback control to confirm the operability of the controller. The second case study showed how the system could be used in a more sophisticated feedings strategy providing fine control and limiting acetate concentration to a low level throughout the fermentation. (c) 1994 John Wiley & Sons, Inc.

No abstract