Improved production of tryptophan in genetically engineered Escherichia coli with TktA and PpsA overexpression

Intracellular precursor supply is a critical factor for amino acid productivity. In the present study, ppsA and tktA genes were overexpressed in genetically engineered Escherichia coli to enhance the availability of two precursor substrates, phosphoenolpyruvate and erythrose-4-phosphate. The engineered strain, TRTH0709 carrying pSV709, produced 35.9 g/L tryptophan from glucose after 40 h in fed-batch cultivation. The two genes were inserted, independently or together, into a low-copy-number expression vector (pSTV28) and transferred to TRTH0709. Fed-batch fermentations at high cell densities of the recombination strains revealed that overexpression of the ppsA gene alone does not significantly increase tryptophan yield. On the other hand, overexpression of the tktA gene, alone or with the ppsA gene, could further improve tryptophan yield to a final tryptophan titer of 37.9 and 40.2 g/L, respectively. These results represent a 5.6% and 11.9% enhancement over the titer achieved by TRTH0709. No evident genetic modifications leading to growth impairment were observed.