Systems engineering of Escherichia coli for high-level hydroxytyrosol production

Hydroxytyrosol (HT) is a potent polyphenolic antioxidant widely utilized in the biomedical and food industries. However, its high-level microbial biosynthesis is primarily hindered by the metabolic flux imbalances and severe cellular toxicity. In this study, an artificial synthetic pathway from 4-hydroxyphenylpyruvate was constructed in an engineered l-phenylalanine producing E. coli chassis. Building on this, the endogenous precursor supply was strengthened via targeted promoter engineering of aroK, aroC, and tyrA, and the heterologous HT biosynthetic pathway was enhanced by overexpressing ARO10. To mitigate intermediate l-DOPA accumulation, co-expression of l-DOPA decarboxylase (DODC) and tyramine oxidase (TYO) reduced l-DOPA by 63.7%, while expression of l-amino acid deaminase (LAAD) reduced l-DOPA by 76.1%. Additionally, precise cofactor engineering was implemented; overexpressing the riboflavin metabolic genes ribH, ribC, and ribF, alongside introducing pntAB, increased HT production by 30.9% and 12.7%, respectively. Furthermore, transcriptomic analysis under HT stress revealed significant upregulation of genes related to transport and stress responses. Among these targets, overexpressing marR substantially improved cellular tolerance and HT production. Finally, during a 5-L bioreactor fermentation supplemented with Fe²⁺ and ascorbic acid, the engineered strain achieved an HT titer of 9.25 g/L, a yield of 0.102 g/g glucose, and a productivity of 0.193 g/L/h. This study reports the highest HT titer to date in E. coli using glucose as the carbon source, providing a robust biomanufacturing platform.