Process development for the enhanced production of L-tyrosine in escherichia coli

Abstract

In an effort to develop a high cell density fermentation platform for L-tyrosine-overproduction in Escherichia coli, various process modifications were investigated in conjunction with screening of metabolically engineered construct in a bioreactor setting. Engineering biosynthetic pathway of aromatic amino acids has been challenging due to the complicated metabolic and regulatory network, where a transcriptional regulator TyrR plays a central role in the regulation of L-tyrosine biosynthesis affecting the gene expression of the nine genes involved in the biosynthesis of aromatic amino acids. Previous efforts on this project searched for key enzymes in L-tyrosine biosynthetic pathway by determining the effects of the combinatorial overexpression of the target enzymes on L-tyrosine production in relation to TyrR regulation. While many efforts have been made into understanding and engineering pathways for L-tyrosine production in Escherichia coli, few investigation have targeted bioprocess related influences on L-tyrosine production. Phosphate limitation was found to be disadvantageous to L-tyrosine production while feed-profile was found to be dependent on the various strains and their knockouts. Additionally, nutrient limitation, temperature, and shear stress were investigated as possible process modifications to enhance L-tyrosine production. Final bioreactor fed-batch fermentation of various constructs were able to produce up to 43.1 g/L L-tyrosine. The results from this study will provide valuable design principles for engineering the aromatic amino acid biosynthetic pathway.