Combinatorial biosynthesis of plant-specific coumarins in bacteria

• Design of artificial biosynthetic pathways of plant coumarins in Escherichia coli.
• Obviation of plant cytochrome P450 enzymes with a promiscuous bacterial hydroxylase.
• Bioconversion of inexpensive phenylpropanoid acids into simple coumarins.
• De novo biosynthesis of umbelliferone and scopoletin.

Coumarins are plant secondary metabolites that have demonstrated a variety of important therapeutic properties, such as antibacterial, anti-inflammatory, and anti-coagulant effects, as well as anti-cancer and anti-AIDS activities. However, knowledge regarding their biosynthesis is relatively limited even for the simplest coumarin molecule, which serves as the gateway molecule to many pharmaceutically important coumarin derivatives. Here we reported the design and validation of artificial pathways leading to the biosynthesis of plant-specific simple coumarins in bacteria. First, Escherichia coli strains were engineered to convert inexpensive phenylpropanoid acid precursors, 4-coumarate and ferulate to simple coumarins, umbelliferone (4.3 mg/L) and scopoletin (27.8 mg/L), respectively. Furthermore, we assembled the complete artificial pathways in E. coli and achieved de novo biosynthesis of umbelliferone and scopoletin without addition of precursors. This study lays the foundation for microbial production of more diverse coumarin compounds.