L-tyrosine (L-tyr) overproducing Escherichia coli strains derived from an L-phenylalanine (L-phe) overproducing strain is characterized in 10 L and 200 L scale fermentations.  Deletion of the chromosomal region encoding for the L-pheA gene, chorismate mutase/preL-phenate dehydratase, its leader peptide (L-pheL) and its associated promoter resulted in significant increase in L-tyr production (1).  Further increase in titer was achieved by overexpressing L-tyrA, encoding chorismate mutase/prephenate dehydrogenase, from a strong non-native trc promoter (1).  Fermentation optimization studies include media component selection; glucose feed optimization, antifoam agent selection, generational stability of the strain, and measurement of rate and yield of product formation. L-tyr titer of 55 g/l in 48 hours was demonstrated in 200 L batches, is the highest titer published till date. 
We have also evaluated two primary separations schemes to isolate and purify L-tyr from the fermentation broth.  Physical separation of L-tyr crystals from biomass using a decanter type centrifuge, based on the density difference between the solids, is compared and contrasted with a strategy where L-tyr is first dissolved at pH=11.5 and then acid precipitated from clarified supernatants following removal of biomass using membrane filtration.  L-tyr product purity of 98% with yields ranging from 90-95% is demonstrated.  

(1) Olson, M. M.; Templeton, L. J.; Suh, W.; Youderian, P.; Sariaslani, F. S.; Gatenby, A. A.; Van Dyk, T. K., Production of tyrosine from sucrose or glucose achieved by rapid genetic changes to phenylalanine-producing Escherichia coli strains. Appl Microbiol Biotechnol 2007, 74, (5), 1031-40.

 (2) Biotechnol Bioeng. 2008 Mar 1; 99(4):741-52