초록
<P>Intracellular precursor supply is a critical factor for amino acid productivity. In the present study, <I>ppsA</I> and <I>tktA</I> genes were overexpressed in genetically engineered <I>Escherichia coli</I> 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 <I>ppsA</I> gene alone does not significantly increase tryptophan yield. On the other hand, overexpression of the <I>tktA</I> gene, alone or with the <I>ppsA</I> 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.</P>