Metabolic Engineering of Candida tropicalis for the De Novo Synthesis of β-Ionone

beta-ionone, a norisoprenoid, is a natural aromatic compound derived from plants, which displays various biological activities including anticancer, antioxidant and deworming properties. Due to its large biomass and strong environmental tolerance, the nonconventional oleaginous yeast Candida tropicalis was selected to efficiently synthesize beta-ionone. We initially investigated the capacity of the cytoplasm and subcellular compartments to synthesize beta-ionone independently. Subsequently, through adaptive screening of enzymes, functional identification of subcellular localization signal peptides and subcellular compartment combination strategies, a titer of 152.4 mg/L of beta-ionone was achieved. Finally, directed evolution of rate-limiting enzyme and overexpression of key enzymes were performed to enhance beta-ionone production. The resulting titer was 400.5 mg/L in shake flasks and 730 mg/L in a bioreactor. This study demonstrates the first de novo synthesis of beta-ionone in C. tropicalis, providing a novel cellular chassis for terpenoid fragrances with considerable industrial potential.