title: L-tyrosine production by deregulated strains of Escherichia coli.
abstract: The excretion of the aromatic amino acid L: -tyrosine was achieved by manipulating three gene targets in the wild-type Escherichia coli K12: The feedback-inhibition-resistant (fbr) derivatives of aroG and tyrA were expressed on a low-copy-number vector, and the TyrR-mediated regulation of the aromatic amino acid biosynthesis was eliminated by deleting the tyrR gene. The generation of this L: -tyrosine producer, strain T1, was based only on the deregulation of the aromatic amino acid biosynthesis pathway, but no structural genes in the genome were affected. A second tyrosine over-producing strain, E. coli T2, was generated considering the possible limitation of precursor substrates. To enhance the availability of the two precursor substrates phosphoenolpyruvate and erythrose-4-phosphate, the ppsA and the tktA genes were over-expressed in the strain T1 background, increasing L: -tyrosine production by 80% in 50-ml batch cultures. Fed-batch fermentations revealed that L: -tyrosine production was tightly correlated with cell growth, exhibiting the maximum productivity at the end of the exponential growth phase. The final L: -tyrosine concentrations were 3.8 g/l for E. coli T1 and 9.7 g/l for E. coli T2 with a yield of L: -tyrosine per glucose of 0.037 g/g (T1) and 0.102 g/g (T2), respectively.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Tina
authors.initials: T
authors.lastname: Lütke-Eversloh
authors.forename: Gregory
authors.initials: G
authors.lastname: Stephanopoulos
mesh_terms: D001709:Biotechnology / Q000379:methods; D003470:Culture Media; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D048168:Escherichia coli K12 / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D005285:Fermentation; D015964:Gene Expression Regulation, Bacterial; D005818:Genetic Engineering / Q000379:methods*; D014443:Tyrosine / Q000096:biosynthesis*
chemical_list: D003470:Culture Media; D029968:Escherichia coli Proteins; D014443:Tyrosine