A bacterial platform for the production of 4-hydroxyphenylacetic acid and its derivatives

4-Hydroxyphenylacetic acid (4-HPAA) and its derivatives, such as homoprotocatechuic acid (3,4-DHBA), homovanillic acid (HVA), and homoisovanillic acid (IHVA), are valuable phenolic acids that exhibit antioxidant, antibacterial and anti-inflammatory properties. They have diverse uses in pharmaceutical, pesticide, and cosmetic industries. Despite their significant importance, microbial production of these chemicals faces challenges such as limited titer or the incomplete understanding of their biosynthetic pathways in microorganisms. In this work, we developed a platform Escherichia coli strain that capable of efficiently producing 4-HPAA by systematical engineering of its biosynthetic pathway. The best engineered strain produced 31.95 g/L of 4-HPAA with a carbon yield of 0.27 g/g glucose, which is the highest titer reported so far. Then, this microbial platform was extended to biosynthesize 3,4-DHBA, HVA and IHVA, by screening hydroxylases and methyltransferases. This led to the de novo production of 3.15 g/L 3,4-DHBA, 102.36 mg/L HVA and 356.74 mg/L IHVA. This work establishes an efficient chassis for producing 4-HPAA and provides a microbial platform for generating its derivatives.