Systematic Engineering of Eriodictyol-7-<i>O</i>-glucoside Biosynthetic Pathway through Enzyme Screening and Gene Regulation

The natural product eriodictyol-7-<i>O</i>-glucoside is more water-soluble and stable than eriodictyol and also exhibits novel biological activities and functions. However, its biosynthesis is hindered by the limited catalytic efficiency of key enzymes. Furthermore, the intricate interplay between cell growth and UDP-glucose supply adds another layer of complexity, rendering the engineering of productive strains challenging. To address this challenge, we introduced a novel "top-down" strategy in which bioinformatics analysis was initially used to identify six specific flavonoid 7-<i>O</i>-glucosyltransferases uniquely capable of converting eriodictyol into its 7-<i>O</i>-glucoside derivative. By manipulation of the plasmid copy number and promoter strength, the expression levels of the most promising flavonoid 7-<i>O</i>-glucosyltransferases from <i>Arabidopsis thaliana</i> were precisely fine-tuned, resulting in a remarkable 66.16% increase in eriodictyol-7-<i>O</i>-glucoside production. To improve the enhancement process, we focused on the overexpression of two pivotal enzymes: phosphoglucose mutase (encoded by the <i>pgm</i> gene) and UDP-glucose pyrophosphorylase (encoded by the <i>galU</i> gene). This strategic step was implemented to significantly increase the availability of glycosylation donors. Moreover, the eriodictyol concentration was increased to ensure ample feedstock. Finally, through comprehensive optimization of the fermentation conditions, eriodictyol-7-<i>O</i>-glucoside production was substantially enhanced, with a staggering 1187.36 mg L^-1 obtained (molar conversion rate: 94.99%) at a substrate titer of 800 mg L^-1 eriodictyol after 48 h of fermentation. The best engineered strain produced 2.70 g L^-1 of eriodictyol-7-<i>O</i>-glucoside in a 5 L bioreactor. This study provides an effective and sustainable method for the high-yield production of flavonoid glycoside derivatives.