Metabolic engineering for improving l-tryptophan production in Escherichia coli

L-Tryptophan is an important aromatic amino acid that is used widely in the food, chemical, and pharmaceutical industries. Compared with the traditional synthetic methods, production of L-tryptophan by microbes is environmentally friendly and has low production costs, and feed stocks are renewable. With the development of metabolic engineering, highly efficient production of L-tryptophan in Escherichia coli has been achieved by eliminating negative regulation factors, improving the intracellular level of precursors, engineering of transport systems and overexpression of rate-limiting enzymes. However, challenges remain for L-tryptophan biosynthesis to be cost-competitive. In this review, successful and applicable strategies derived from metabolic engineering for increasing L-tryptophan accumulation in E. coli are summarized. In addition, perspectives for further efficient production of L-tryptophan are discussed.