Metabolic engineering of Escherichia coli for the enhanced production of l‐tyrosine

Abstract Despite wide applications of l ‐tyrosine in the market, microbial overproduction of l ‐tyrosine has been a great challenge due to the complex gene regulations involved in its biosynthetic pathway. To this end, effects of knocking out tyrR on the l ‐tyrosine production were further explored during the strain development. Also, blocking cellular uptake of l ‐tyrosine by knocking out tyrosine transporters was examined with respect to l ‐tyrosine production. Using feedback‐resistant aroG and tyrA genes ( aroG fbr and tyrA fbr hereafter) as initial overexpression targets, which encode 3‐deoxy‐7‐phosphoheptulonate synthase and chorismate mutase or prephenate dehydrogenase, respectively, various combinations of genes were subsequently overexpressed in the Escherichia coli wild‐type and tyrR knockout strain, and their effects on the l ‐tyrosine production were examined. Co‐overexpression of aroG fbr , aroL and tyrC , a gene from Zymomonas mobilis functionally similar to tyrA fbr , but insensitive to l ‐tyrosine, led to the greatest l ‐tyrosine production regardless of the strains and plasmid constructs examined in this study. The strain BTY2.13 overexpressing the abovementioned three genes together with the removal of the l ‐tyrosine‐specific transporter ( tyrP ) produced 43.14 g/L of l ‐tyrosine by fed‐batch fermentation using the exponential feeding followed by DO‐stat feeding method. This outcome suggested that the tyrR gene knockout was not mandatory for the l ‐tyrosine overproduction, but the production performance of strains having tyrR appeared to be highly affected by vector systems and feeding methods. With an optimal vector system and a feeding method, tyrP knockout appeared to be more effective in enhancing the l ‐tyrosine than tyrR knockout.