Optimized Bioconversion of Naringenin to Hesperetin in Escherichia coli With Halide Methyltransferase-Mediated S-Adenosylmethionine Regeneration

Hesperetin is a bioactive flavonoid with potential applications in pharmaceuticals and nutraceuticals, yet its low natural abundance limits commercial use. In this study, a two-step whole-cell bioconversion process was developed for the microbial production of hesperetin from naringenin in Escherichia coli. The 4-hydroxyphenylacetate-3-hydroxylase enzyme complex (HpaBC) enabled cytochrome P450-independent conversion of naringenin to eriodictyol. Subsequent 4′-O-methylation was achieved using a plant-derived flavonoid 4'-O-methyltransferase (FOMT) coupled with a halide methyltransferase (HMT) for in situ S-adenosylmethionine (SAM) regeneration. Enzyme activity was first confirmed individually in vitro and in vivo, followed by integration into recombinant whole-cell systems, co-expressing all desired enzymes. Process optimization through delayed co-substrate addition, improving induction conditions, and machine learning-guided parameter selection increased hesperetin yields up to 70.6% with minimal byproduct formation. This work demonstrates the feasibility of combining process development and digital optimization strategies for the sustainable production of methylated flavonoids in microbial systems. The resulting E. coli platform provides a scalable blueprint for future biotechnological applications involving cofactor-dependent plant secondary metabolism.