L ‐Tyrosine production by recombinant Escherichia coli : Fermentation optimization and recovery

L ‐Tyrosine ( L ‐tyr) overproducing Escherichia coli strain 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 pheA gene, chorismate mutase/prephenate dehydratase, its leader peptide ( pheL ) and its associated promoter resulted in significant increase in L ‐tyr production (Olson et al., 2007. Appl Microbiol Biotechnol 74(5):1031–1040). Further increase in titer was achieved by overexpressing tyrA , encoding chorismate mutase/prephenate dehydrogenase, from a strong non‐native trc promoter (Olson et al., 2007. Appl Microbiol Biotechnol 74(5):1031–1040). Fermentation optimization studies include media component selection; glucose feed optimization, antifoam agent selection, and understanding fermentation parameters affecting foaming. Generational stability of the strain was evaluated along with rate, titer, and yield of tyrosine formation from glucose. L ‐tyr titer of 55 g/L in 48 h 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% to 95% is demonstrated. Biotechnol. Bioeng. 2008;99: 741–752. © 2007 Wiley Periodicals, Inc.