Abstract
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 (pta1) from E. coli CCTCC M 2016009, forming strain FB-04(pta1). Pta1 exhibits lower catalytic capacity and substrate affinity than Pta because of a single amino acid substitution (Pro69Leu). FB-04(pta1) lacked the growth defect of FB-04(Δpta) and showed improved fermentation performance. Strain FB-04(pta1) 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(pta1) was slower than that by FB-04. The final L-tryptophan titer of FB-04(pta1) reached 44.0 g/L, representing a 15% increase over that of FB-04. Metabolomics analysis showed that the pta1 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.
Highlights
L-tryptophan, an essential amino acid that is a precursor of other important biomolecules, such as the neurotransmitter serotonin, is widely used in medicine, food, and animal feed [1, 2]
Sequence comparison of genes involved in the formation of acetate in E. coli FB-04 and E. coli CCTCC M 2016009
When they are grown under the same fermentation conditions, less acetate is secreted by E. coli CCTCC M 2016009 than by E. coli FB-04
Summary
L-tryptophan, an essential amino acid that is a precursor of other important biomolecules, such as the neurotransmitter serotonin, is widely used in medicine, food, and animal feed [1, 2]. The L-tryptophan biosynthetic pathway in microorganisms, which involves central metabolism, the common aromatic pathway and the L-tryptophan branch pathway, is long and its regulation is complicated [3,4,5]. The high industrial relevance of Escherichia coli has stimulated efforts to improve L-tryptophan yield by analyzing the underlying metabolic regulatory networks of L-. Ltd for assistance with the GC-MS experiments and data analysis. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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