Modification of tryptophan transport system and its impact on production of L-tryptophan in Escherichia coli.

The production of L-tryptophan through chemical synthesis, direct fermentation, bioconversion and enzymatic conversion has been reported. However, the role of transport system for aromatic amino acids in L-tryptophan producing strains has not been fully explored. In this study, the fact was revealed that L-tryptophan production and cell growth were affected by the modification of transport systems based on YddG functioning as aromatic amino acid excretion and AroP functioning as general aromatic amino acid permease. Through comparing glucose conversion rates of recombinant strains such as Escherichia coli TRTH ΔaroP, E. coli TRTH-Y, and E. coli TRTH ΔaroP-Y, the moderate modification of transport system resulted in the metabolic flux redistribution of L-tryptophan biosynthesis pathway. In the fed-batch fermentation by E. coli TRTH and E. coli TRTH-Y in 30-liter fermentor, the final production of L-tryptophan fermented by E. coli TRTH-Y was 36.3 g/L, which was 12.6% higher than fermentation by E. coli TRTH.