Metabolic engineering of<i> Corynebacterium</i><i> glutamicum</i> for L-tyrosine production from glucose and xylose

Microbial production of aromatic compounds is an attractive and sustainable biotechnological approach. With this motivation, here metabolic engineering of Corynebacterium glutamicum for L-tyrosine (L-Tyr) overproduction was attempted by pushing the carbon flux more towards L-Tyr. Translational start codon exchanges of prephenate dehydratase (pheA), anthranilate synthase (trpE), and phenylalanine aminotransferase (pat) genes revealed that reduced expression of pheA was the major contributor to increased L-Tyr titer while codon exchange in trpE was effective to a lower extent. Overexpression of aroE and qsuC, encoding shikimate dehydrogenase and 3-dehydro-quinate dehydratase, respectively, and of dapC (cg1253), which is predicted to encode prephenate amino-transferase, were futile to increase L-Tyr titer. Similarly, deletion of the qsuABD gene cluster had also not enhanced titer. As for increasing precursor supply, deletion of ptsG of glucose uptake and overexpression of inositol permease (iolT2) and glucokinase (glcK) were not effective, but with utilization of xylose, enabled by overexpression of xylose isomerase (xylA) and xylulokinase (xylB), titer improved. Highest L-Tyr titer using the construct was 3.1 g/L on glucose and 3.6 g/L on a 1:3 (w/v) mixture of glucose and xylose. This result displays the potential of the constructed strain to produce L-Tyr from lignocellulosic renewable carbon sources.