Demonstrating and engineering the de novo synthesis of two aromatic chemicals estragole and anethole in Escherichia coli

Abstract

Estragole and anethole are the major flavoring and aroma components of the essential oils extracted from basil (Ocimum basilicum L.), anise (Pimpinella anisum), star anise (Illicium verum), and fennel (Foeniculum vulgare). Besides, they also exhibit bioactivities, such as antioxidation, antimicrobial, immunomodulation, inti-inflammation, and anti-diabetes. These properties make them being faced with substantial applications in the industries of food, cosmetics, pharmaceutics, and agriculture. Commercial estragole and anethole are currently obtained from extraction from their original plants, which suffers from unstable quality and resources. Microbial synthesis is a promising alternative approach to sustainably obtain estragole and anethole, but has not been achieved. In this study, we modularly redesigned the synthetic pathways based on the Escherichia coli chassis. Firstly, a p-coumaryl alcohol over-accumulator (436.28 mg/L) was engineered to facilitate the validation of the undemonstrated downstream module. De novo biosynthesis of estragole and anethole was achieved by stepwise analysis and BioBricks assembly. The intracellular availability of S-adenosyl-L-methionine (SAM) was revealed to be the key limiting factor, and was enhanced by deregulating the synthesis. Finally, the productions of estragole and anethole were improved by 246.88% and 202.44% compared with the initial strains. This study represents the first synthesis of estragole and anethole in microbial chassis, and the demonstration of microbial synthesis of propenyl phenols. Besides, it provided an alternative sustainable approach to obtain flavoring and aroma chemicals.