A process has been developed for production of L-tyrosine. The process, demonstrated at 10 and 200 liter scale, uses overproducing Escherichia coli strains derived from an L-phenylalanine overproducing strain. Significant increase in L-tyrosine production was achieved via deletion of the chromosomal region encoding for the pheA gene, chorismate mutase/prephenate dehydratase, its leader peptide (pheL) and its associated promoter. A further increase in titer was achieved by overexpressing tyrA, encoding chorismate mutase/prephenate dehydrogenase, from a strong non-native trc promoter. Fermentation optimization studies were done, with particular emphasis on conditions to mitigate foaming issues associated with running a three-phase fermentation (media, air and tyrosine crystals). L-tyrosine titers of 55 g/l in 48 hours were demonstrated at the 200 L scale, which is the highest titer reported at that time..

Two primary separations schemes for isolation and purification of L-tyrosine from the fermentation broth were evaluated. The first uses physical separation of tyrosine crystals via selective centrifugation, while the second involves dissolving the tyrosine at high pH, filtering to remove biomass, then recovering the tyrosine by acid precipitation. L-tyrosine product purity of 98% was achieved with yields ranging from 90-95%.