Multi-Layered Engineering of Aspergillus terreus Enhances Biosynthesis of the Plant-Derived Fungicide Physcion

Abstract Background Emodin and its derivatives are important bioactive anthraquinones from rhubarb, with diverse pharmacological activities. Physcion, an O-methylated derivative of emodin, is a promising plant-derived fungicide and pharmaceutical lead. However, plant extraction yields are low and land-intensive, while microbial production is hampered by inefficient conversion and byproduct accumulation. Results Here, we identify a cytochrome P450 enzyme (CYP-H6231) that, with its dedicated redox partner cytochrome P450 reductase CPR-H10273, converts emodin to ω-hydroxyemodin in Aspergillus terreus. Deletion of CYP-H6231 increased physcion titer by 1.8-fold and significantly improved product purity. Further engineering, via 3-O-methyltransferase overexpression, SAM pathway enhancement, and enzyme fusion, yielded only modest improvement (up to 37%), likely due to compromised strain robustness from the loss of CYP-H6231 mediated detoxification. Structural modeling and mutagenesis of CYP-H6231 revealed key residues for substrate recognition and catalysis. Conclusions This study reveals a detoxification bottleneck in anthraquinone biosynthesis and establishes two improved A. terreus platforms for scalable production of physcion and emodin, respectively, highlighting trade-offs between pathway efficiency and cellular fitness.