Determination of the maximum specific uptake capacities for glucose and oxygen in glucose-limited fed-batch cultivations of Escherichia coli

A simple pulse-based method for the determination of the maximum uptake cap acities for glucose a nd oxygen in glucose limited cultivations of E. coli is presented. The method does not depend on the time-consuming analysis of glucose or acetate, and therefore can be used to control the feed rate in g lucose limited cultivations, such as fed-batch processes. The application o f this method in fed-batch processes of E. coli showed that the uptake capa city for neither glucose nor oxygen is a constant parameter, as often is as sumed in fed-batch models. The glucose uptake capacity decreased significan tly when the specific growth rate decreased below 0.15 h(-1) and fell to ab out 0.6 mmol g(-1) h(-1) (mmol per g cell dry weight and hour) at the end o f fed-batch fermentations, where mu was approximately 0.02 h(-1). The oxyge n uptake capacity started to decrease somewhat earlier when mu declined bel ow 0.25 h(-1) and was 5 mmol g(-1) h(-1) at the end of the fermentations. T he behavior of both uptake systems is integrated in a dynamic model which a llows a better fitting of experimental values for glucose in fed-batch proc esses in comparison to generally used unstructured kinetic models. (C) 2001 John Wiley & Sons, Inc.