One-pot biocatalytic upgrading of lignin-derived phenol and catechol to hydroxytyrosol

Abstract

Upgrading lignin-derived monomeric products presents a compelling prospect for synthesizing value-added products. Despite the potential benefits, the conversion of lignin-derived phenols into hydroxytyrosol (HT), a potent natural antioxidant predominantly sourced from olives, remains underexplored. Herein, we envisioned three novel one-pot cascade biocatalytic approaches for converting lignin-derived catechol and phenol into HT by integrating four or five main reactions: C–C coupling, hydroxylation, decarboxylation, deamination and reduction. By co-expressing the corresponding enzymes in recombinant Escherichia coli (E. coli) resting cells, we achieved HT conversions of 65.4% and 89.0% from 10 mM catechol using recombinant E. coli (CFK-RTA) resting cells, which co-expressed tyrosine phenol-lyase (FnTPL), tyrosine decarboxylase (TDC), amine transaminase (ATA) and aldehyde reductase (yahK), and E. coli (RFK-EAL) resting cells, which co-expressed FnTPL, L-amino acid deaminase (LAAD), α-keto acid decarboxylase (ARO10) and yahK, respectively. Additionally, a 75.3% conversion of HT from 10 mM phenol was achieved with E. coli (CFK-EBC-RAL) resting cells co-expressing FnTPL, 4-hydroxyphenylacetate 3-hydroxylase (HpaBC), LAAD, ARO10 and yahK. The highest HT titers of 20.6 mM (3.18 g L⁻¹) and 18.5 mM (2.85 g L⁻¹) were obtained from 30 mM catechol and phenol, respectively, by utilizing recombinant E. coli (RFK-EAL) and E. coli (CFK-EBC-RAL) resting cells in a fed-batch strategy. These cascade biocatalysis processes rely on biomass-derived phenol or catechol and inexpensive pyruvate as substrates, with NH₄Cl serving as the amine donor, offering new and viable routes for the sustainable and environmentally friendly production of HT.