Physiologically motivated strategies for control of the fed-batch cultivation of recombinant Escherichia coli for phenylalanine production

The efficiency of the fed-batch cultivation of recombinant Escherichia coli AT2471 for phenylalanine production is highly dependent on the distribution of the carbon flow between the main process products — biomass, phenylalanine, acetic acid and carbon dioxide. In order to enhance the process performance, the effects of several factors, namely glucose feeding, tyrosine feeding and oxygen supply, were investigated experimentally. As a result, a set of control strategies was developed, designed to tolerate phenylalanine synthesis at the expense of the remaining products. The DO was controlled to prevent acetic acid excretion due to oxygen limitation. The total amount of tyrosine fed was used to provide an optimal balance between biomass synthesis and that of phenylalanine. Special algorithms for control of the glucose feed rate were applied to eliminate the threat of acetic acid excretion due to overfeeding, and at the same time, to reduce excessive CO₂ evolution caused by unnecessarily severe glucose limitation. The joint application of these strategies resulted in greatly improved efficiency in the phenylalanine production process: the final phenylalanine concentration reached 46 g/l, the yield was above 17%, and the productivity-0.85 g/l·h. In combination, these data exceed the results reported by others, and are much higher than those obtained by use before the implementation of the proposed complex of techniques.