Engineering of Hydroxytyrosol Production in Escherichia coli for Industrial Application

Hydroxytyrosol (HTy) is one of the most powerful antioxidants and has a wide range of potential applications in industry. Currently, HTy is produced from enriched olive extracts after chemical or enzymatic hydrolysis, but microbial fermentation can be a promising solution of an increasing demand for stable and sustainable production.

We have previously reported a synthetic pathway in E. coli capable of producing HTy from tyrosine. Our synthetic HTy pathway consists of five heterologous genes for tyrosine hydroxylation and downstream conversion of L-DOPA to HTy. Although we have shown that this pathway is functional, the low titer from tyrosine or from glucose remained as an issue to be addressed. Here we report three metabolic engineering efforts to improve the efficiency of the synthetic HTy pathway. First, we have engineered the co-factor biosynthetic pathway for tyrosine hydroxylation. Next, we have identified inhibition of the tyrosine hydroxylation by downstream chemicals and applied co-culture strategy to overcome it. Lastly, the gene expression of pathway enzymes was optimized using metabolomics and proteomics data. With these engineering, we were able to improve the product yield from tyrosine about 3-fold. In addition, we have engineered the host strain to overproduce tyrosine. Using this engineered strain, we confirmed the production of L-DOPA from glucose without any external supplementation of tyrosine, and the resulting L-DOPA was further converted into HTy by co-culture strategy with an improved yield from the previous result.