A One-Pot, Whole-Cell Biocatalysis Approach for Vanillin Production using Lignin Oil

Abstract

Vanillin is a popular and versatile flavor compound, almost entirely produced from petroleum-derived phenol by a multi-step chemical synthesis. The process is hazardous to the environment and unsustainable for its fossil oil usage. Therefore, developing environmentally friendly, efficient, and sustainable routes to biobased vanillin is essential. Here, we report on vanillin production from 4-n-propylguaiacol (4PG), one of the main components in lignin oil obtained through reductive catalytic fractionation (RCF) of soft wood, by employing recombinant Escherichia coli cells. Conversion is based on the expression of two engineered oxidative enzymes: a 4-n-propylguaiacol oxidase and an isoeugenol dioxygenase. A high yield of vanillin, 66% from 4PG in RCF lignin oil was achieved through rounds of optimisation of the whole-cell conversion process. This high-performance strategy was readily scaled up to produce vanillin at an unprecedented 18% and 3% yield based on lignin oil and spruce wood respectively. The whole-cell bioconversion process shows good tolerance even at high loadings of starting material, showcasing the robustness and applicability of the employed biocatalysts. This work paves the way for further development towards the efficient production of high-titer biobased vanillin using depolymerised lignin as the feedstock.