Metabolic Engineering of Escherichia coli Nissle 1917 for Efficient Production of Caffeic Acid

Caffeic acid, a natural phenolic acid with antioxidant and antibacterial properties, is a high-quality natural additive widely used in various food processing. In this study, the probioticEscherichia coliNissle 1917 was selected as the host for producing caffeic acid. First, the competitive branch of the precursor l-tyrosine was blocked, resulting in the mutant strain WNZ05. Then, the quorum sensing system was introduced into WNZ05 to dynamically supply l-tyrosine, which was used as a switch plasmid to coordinate the expression of FjTAL, hpaBC, and ycjP. The SAM5 gene was also introduced to reduce the intermediate products p-coumaric acid, achieving efficient flow of the metabolic pathway toward caffeic acid. Ultimately, the engineered strain produced 1.87 g/L caffeic acid in shake flasks and a record 13.92 g/L via fed-batch fermentation in a 2.5 L bioreactor, the highest microbial yield reported to date.