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L- Tyrosine production by deregulated strains of Escherichia coli

Lütke-Eversloh, Tina, Stephanopoulos, Gregory
Applied microbiology and biotechnology 2007 v.75 no.1 pp. 103-110
Escherichia coli K12, batch fermentation, biosynthesis, cell growth, excretion, gene overexpression, glucose, structural genes, tyrosine
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.