Abstract
LβTyrosine (Lβtyr) overproducing Escherichia coli strain derived from an Lβphenylalanine (Lβphe) 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 Lβtyr production (Olson et al., 2007. Appl Microbiol Biotechnol 74(5):1031β1040). Further increase in titer was achieved by overexpressing tyrA, encoding chorismate mutase/prephenate dehydrogenase, from a strong nonβnative trc promoter (Olson et al., 2007. Appl Microbiol Biotechnol 74(5):1031β1040). 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. Lβtyr 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 Lβtyr from the fermentation broth. Physical separation of Lβtyr crystals from biomass using a decanter type centrifuge, based on the density difference between the solids, is compared and contrasted with a strategy where Lβtyr is first dissolved at pH 11.5 and then acid precipitated from clarified supernatants following removal of biomass using membrane filtration. Lβtyr product purity of 98% with yields ranging from 90% to 95% is demonstrated. Biotechnol. Bioeng. 2008;99: 741β752. Β© 2007 Wiley Periodicals, Inc.