The improved L-tryptophan production in recombinant Escherichia coli by expressing the polyhydroxybutyrate synthesis pathway.

Polyhydroxybutyrate (PHB), the best known polyhydroxyalkanoates (PHA) has been believed to change intracellular metabolic flow and oxidation/reduction state, as well as enhance stress resistance of the host. In this study, a PHB biosynthesis pathway, which contains phaCAB operon genes from Ralstonia eutropha, was introduced into an L-tryptophan producing Escherichia coli strain GPT1002. The expression of the PHB biosynthesis genes resulted in PHB accumulation inside the cells and improved the L-tryptophan production. Quantitative real-time PCR analysis showed that the transcription of tryptophan operon genes in GPT2000 increased by 1.9 to 4.3 times compared with the control, indicating that PHB biosynthesis in engineered E. coli changed the physiological state of the host. Xylose was added into the medium as co-substrate to enhance the precursor supply for PHB biosynthesis. The addition of xylose improved both extracellular L-tryptophan production and intracellular PHB accumulation. Moreover, we obtained 14.4 g l(-1) L-tryptophan production and 9.7 % PHB (w/w) accumulation in GPT2000 via fed-batch cultivation.