Microbial Biosynthesis of β-Ionone and Its Hydroxylated Derivative via Enzyme and Metabolic Engineering

Ionone and its hydroxylated derivatives are valuable aroma and bioactive compounds derived from the oxidative cleavage of carotenoids. Microbial biosynthesis of these compounds has gained interest due to its sustainability, product specificity, and potential for industrial-scale production. Here, we developed a modular microbial platform using engineered Escherichia coli strains to produce β-ionone and hydroxylated derivatives from glycerol. The β-ionone-producing strain harnessed a protein-engineered carotenoid cleavage dioxygenase 1 from Petunia hybrida (PhCCD1^S428C) in a reconstructed β-ionone biosynthetic pathway and produced 54.2 mg/L β-ionone, a 1.7-fold increase compared with the wild-type control; and the β-ionone hydroxylation strain expressed a mutated cytochrome P450 from Bacillus megaterium (BM3P450^F87S), converting α/β-ionone to 4-OH-β-ionone and 3-OH-α/β-ionone. By assembling these two optimized modules in a coculture system, 4.18 mg/L of 4-OH-β-ionone was biosynthesized. This study establishes a modular microbial route to produce ionone and its hydroxylated derivatives via β-ionone hydroxylation, thereby avoiding the cleavage of hydroxylated carotenoids.