Bioconversion of Lignin-Derived Feedstocks to Muconic Acid by Whole-Cell Biocatalysis

Lignin as a byproduct can be obtained from agricultural wastes and biorefinery. In this study, we sought to develop Escherichia coli-based whole-cell biocatalysis for converting lignin-derived isoeugenol into cis,cis-muconic acid (ccMA). Recombinant E. coli expressing aromatic dioxygenase from Thermothelomyces thermophila and aldehyde dehydrogenase from Saccharomyces cerevisiae could efficiently convert isoeugenol to vanillic acid (VAN). However, we found that the demethylation of VAN by VanAB from Pseudomonas putida was severely inhibited by a high concentration of isoeugenol, which prompted us to develop a two-step approach to the production of ccMA from isoeugenol. Upon adjustment of the feeding strategy and optimization of the pH conditions, 43.8 mM ccMA was produced from 50 mM isoeugenol-derived VAN by recombinant E. coli expressing VanAB from P. putida, GDC from Talaromyces atroroseus, and CatA from Acinetobacter radioresistens. This work is a pioneering study in the evaluation of E. coli-based whole-cell biocatalysis for lignin valorization.