Improvement of the production of L-tryptophan in Escherichia coli by application of a dissolved oxygen stage control strategy

Dissolved oxygen (DO) is a key parameter for the production of L-tryptophan, and maintenance of appropriate DO levels can be used to increase the formation of L-tryptophan and reduce the accumulation of acetate and glutamate. In addition, controlling the level of DO by adjusting the feeding rate of glucose solution affects the concentration of glucose in the fermentation process. In this study, the effects of DO levels on L-tryptophan production were investigated, and four strategies of DO stage control were developed for use in L-tryptophan fermentation. The results indicate that the application of DO stage control I (20 % oxygen at 0–20 h, 30 % at 20–38 h) during L-tryptophan fermentation resulted in the highest dry cell weight (51.2 g/L) and production of L-tryptophan (46.8 g/L), which were 1.10 and 1.28 times as high, respectively, as those obtained during DO stage control III (50 % oxygen at 0–20 h and 20 % at 20–38 h). Additionally, the total glucose conversion percentage with DO stage control I was 17.2 %, which was 13.16 % higher than that of DO stage control III. Furthermore, the metabolic flux distribution with DO stage control I and III revealed greater carbon flux into the pentose phosphate pathway, while the flux of byproducts (acetate, glutamate, and lactate) was lower during DO stage control I. Finally, the flux of tryptophan with DO stage control I was 19.3 %, which was 1.79 times as high as that obtained with DO stage control III.