Fermentative Produktion von L-Phenylalanin mit Escherichia coli und integrierter Produktabtrennung

In this work a fermentation process with integrated product separation for the production of L-phenylalanine with recombinant Escherichia coli was developed. The aromatic amino acid L-phenylalanine is used for the production of the low-calorie sweetener aspartame. It is one of the most important commercially produced amino acids. In contrast to the chemo-enzymatic processes enantiomeric pure L-phenylalanine can be produced in fermentation processes based on glucose. Therefore, technical approaches were investigated to improve the L-phenylalanine production, based on a 20 l fed-batch fermentation process with control of glucose and L-tyrosine feeding. Recombinant L-tyrosine auxotrophic E. coli strains with deregulations in the aromatic biosynthesis pathway and different glucose uptake systems were used. Investigations of the L-phenylalanine production with different strains showed that the glucose concentration suitable for production is dependent on the glucose uptake system of the strain. The best production strain was identified and used for investigations of the in uence of process parameters as temperature, pH and medium components. The space-time yield was highest at 37 $^\circ$C but production was inhibited by high L-phenylalanine concentration (>180-200 mmol/l). To avoid a product inhibition and improve the production process a novel approach for integrated separation of L-phenylalanine from a fermentation process with cation-selective reactive extraction in centrifugal extractors was developed. In offline experiments good phase separation and stability of the system were shown. Suitable conditions for online extraction were identified. By integration of reactive extraction from cell and protein free permeate in the fermentation process the production phase was significantly extended and 0,25 mmol/(g$\cdot$h) L-phenylalanine produced until the end of the fermentation. The byproduct formation was reduced and L-phenylalanine concentrated via the extraction. The product concentration was increased by 34 % and the product-substrate selectivity was increased by 28 % relative to the process without integrated separation