초록
<P>Acetate accumulation during the fermentation process of <I>Escherichia coli</I> FB-04, an L-tryptophan production strain, is detrimental to L-tryptophan production. In an initial attempt to reduce acetate formation, the phosphate acetyltransferase gene (<I>pta</I>) from <I>E</I>. <I>coli</I> FB-04 was deleted, forming strain FB-04(<I>Δpta</I>). Unfortunately, FB-04(<I>Δpta</I>) exhibited a growth defect. Therefore, <I>pta</I> was replaced with a <I>pta</I> variant (<I>pta</I>1) from <I>E</I>. <I>coli</I> CCTCC M 2016009, forming strain FB-04(<I>pta</I>1). Pta1 exhibits lower catalytic capacity and substrate affinity than Pta because of a single amino acid substitution (Pro69Leu). FB-04(<I>pta</I>1) lacked the growth defect of FB-04(<I>Δpta</I>) and showed improved fermentation performance. Strain FB-04(<I>pta</I>1) showed a 91% increase in L-tryptophan yield in flask fermentation experiments, while acetate production decreased by 35%, compared with its parent FB-04. Throughout the fed-batch fermentation process, acetate accumulation by FB-04(<I>pta</I>1) was slower than that by FB-04. The final L-tryptophan titer of FB-04(<I>pta</I>1) reached 44.0 g/L, representing a 15% increase over that of FB-04. Metabolomics analysis showed that the <I>pta</I>1 genomic substitution slightly decreased carbon flux through glycolysis and significantly increased carbon fluxes through the pentose phosphate and common aromatic pathways. These results indicate that this strategy enhances L-tryptophan production and decreases acetate accumulation during the L-tryptophan fermentation process.</P>