Tyrosol is an essential precursor of oleuropein, hydroxytyrosol and salidroside. Thus, it is of great importance to build a strain with high tyrosol production. In this study, Escherichia coli BL21 (DE3) was chosen as the host strain, because it can reproduce quickly and it is easy to make gene manipulations. Aromatic aldehyde synthase (AAS) from Petroselinum crispum was overexpressed by a native constitutive promoter PcspA with a plasmid pRSFDuet-1, resulting in 105.97 mg/L of tyrosol. Then PcAAS was overexpressed in a mutant strain with phenylalanine (pheA), pyruvate (ptsG, crr, pykF) and hydroxyphenylacetic acid (feaB) competition pathway knocked out and feedback inhibition released (tyrR), resulting in 1 055.36 mg/L of tyrosol production. In order to further strengthen the metabolic flux, five alcohol dehydrogenase candidates were screened (AdhE, AdhP, YahK, FrmA from E. coli and Adh6 from Saccharomyces cerevisiae). The results showed that Adh6 from S. cerevisiae had the highest dehydrogenase activity, producing 1 516.86 mg/L of tyrosol, which was improved by 43.73%. Besides, combinatorial promoter engineering of aas and adh6 was applied to optimize the metabolic flux, as a result, 1 810.46 mg/L tyrosol was produced. Finally, fermentation optimizations on carbon source, nitrogen source and CaCO3 were conducted on shaking flasks. The titer of tyrosol increased to 2 120.58 mg/L, rising by 17.13%. The results lay a good foundation for the further researches of tyrosol and related downstream products.
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