L-Tryptophan Production in Escherichia coli Improved by Weakening the Pta-AckA Pathway

Acetate accumulation during the fermentation process of Escherichia coli 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 ( pta ) from E . coli FB-04 was deleted, forming strain FB-04( Δpta ). Unfortunately, FB-04( Δpta ) exhibited a growth defect. Therefore, pta was replaced with a pta variant ( pta 1) from E . coli CCTCC M 2016009, forming strain FB-04( pta 1). Pta1 exhibits lower catalytic capacity and substrate affinity than Pta because of a single amino acid substitution (Pro69Leu). FB-04( pta 1) lacked the growth defect of FB-04( Δpta ) and showed improved fermentation performance. Strain FB-04( pta 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( pta 1) was slower than that by FB-04. The final L-tryptophan titer of FB-04( pta 1) reached 44.0 g/L, representing a 15% increase over that of FB-04. Metabolomics analysis showed that the pta 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.