High-Level Production of Hydroxytyrosol in Engineered Saccharomyces cerevisiae

Hydroxytyrosol (HT) is a valuable aromatic compound with numerous applications. Herein, we enabled the efficient and scalable de novo HT production in engineered Saccharomyces cerevisiae (S. cerevisiae) from glucose. Starting from a tyrosol-overproducing strain, six HpaB/HpaC combinations were investigated, and the best catalytic performance was acquired with HpaB from Pseudomonas aeruginosa (PaHpaB) and HpaC from Escherichia coli (EcHpaC), resulting in 425.7 mg/L HT in shake flasks. Next, weakening the tryptophan biosynthetic pathway through downregulating the expression of TRP2 (encoding anthranilate synthase) further improved the HT titer by 27.2% compared to the base strain. Moreover, the cytosolic NADH supply was improved through introducing the feedback-resistant mutant of the TyrA (the NAD⁺-dependent chorismate mutase/prephenate dehydrogenase, TyrA*) from E. coli, which further increased the HT titer by 36.9% compared to the base strain. The best performing strain was obtained by optimizing the biosynthesis of HT in S. cerevisiae through a screening for an effective HpaB/HpaC combination, biosynthetic flux rewiring, and cofactor engineering, which enabled the titer of HT reaching 1120.0 mg/L in the shake flask. Finally, the engineered strain produced 6.97 g/L of HT by fed-batch fermentation, which represents the highest titer for de novo HT biosynthesis in microorganisms reported to date.