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© 2022 Elsevier B.V.Lignocellulosics are abundant carbon sources in nature, therefore they gain increasing attention in biotechnology for production of value-added chemicals. In this proof-of-concept study highlighting the techno-economic potential of L-3,4-dihydroxyphenylalanine (L-DOPA) production from lignocellulosic agro-waste hazelnut husk, first an exploratory model-based optimization was used to release the sugar content of the husk whilst maximizing sugar concentration. The sugar hydrolysate was then evaluated as a feedstock for production using an engineered Corynebacterium glutamicum strain. Optimal treatment conditions were found by Kriging model as 12.5% husk load with 3.8% acid for 50 min at 121 °C, which gave a hydrolysate of 27.67 g L−1 reducing sugar with a yield of 11.07 g sugar/100 g husk. When this hydrolysate was used as the sole carbon source during fermentative production, 20 ± 0.4 mg L−1 of L-DOPA was produced. When cells grown on husk hydrolysate were used for whole-cell biotransformation, a titer of 82 ± 1 mg L−1 of L-DOPA was obtained. From an economical point of view, the titer obtained during fermentative production would allow production of L-DOPA from hazelnut husk right around the breakeven point. However, further engineering of the strains and optimization of bioprocess conditions, would make it possible to bring the revenues to higher levels.

© 2023 Elsevier B.V.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-dehydroquinate dehydratase, respectively, and of dapC (cg1253), which is predicted to encode prephenate aminotransferase, 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.