Genetic and Bioprocess Engineering for the Selective and High-Level Production of Geranyl Acetate in Escherichia coli

Geranyl acetate is, as one of the monoterpenoids, a natural constituent of more than 60 essential oils. Production of such an ester fragrance compound by plant extracts is limited by low yield and high processing costs but plausible by microbial synthesis. We report a microbial cell factory that realizes selective and high-level geranyl acetate production in Escherichia coli. For this purpose, co-expression of geraniol synthase and alcohol acetyltransferase was initially used to increase production yield, but a considerable quantity of precursor geraniol was also produced. Further, introducing an extra AAT gene copy and controlling the substrate glycerol supply enabled a drastically higher selective geranyl acetate production. Eventually, the highest reported titer of 52.78 mM (equivalent to 10.36 g/L) geranyl acetate, accounting for 98.5% of total products, was achieved under a controlled fermentation system. Such selective and high-level geranyl acetate production by combining genetic and bioprocess engineering is also a promising strategy for other monoterpene esters in E. coli.