Enhanced Production of L-Tryptophan with Glucose Feeding and Surfactant Addition and Related Metabolic Flux Redistribution in the Recombinant Escherichia coli

The production of L-tryptophan was investigated in a recombinant strain Escherichia coli W3110-ZDrr. It was observed that phosphate and feeding strategies are key factors to ensure the good cell growth and high production of L-tryptophan. The simple exponential feeding strategy could only produce 10.6 g/L L-tryptophan due to the improper feeding rate; while the manual glucose-feedback feeding approach could effectively control the substrate and inhibit the formation of acetate, and thus improvemed the L-tryptophan production to 25.5 g/L. The modified exponential feeding approach avoided overfeeding or underfeeding and achieved high production of L-tryptophan. Moreover, the addition of Tween 60 or PL61 could enhance the cell growth and the production of L-tryptophan in the fed-batch mode. Subsequent metabolic flux analysis showed that more carbon flux was distributed into the biosynthesis of L-tryptophan when Tween 60 or PL61 was supplied. The present work presents one base for further large-scale production of this important amino acid.