Vanillic acid and methoxyhydroquinone production from guaiacyl units and related aromatic compounds using Aspergillus niger cell factories

Ronnie J M Lubbers,Adiphol Dilokpimol,Pieter C A Bruijnincx,Răzvan C Cioc,Jaap Visser,Paula A Nousiainen,Ronald P De Vries

doi:10.1186/s12934-021-01643-x

Ronnie J M Lubbers, Adiphol Dilokpimol + Show 5 more

Open Access

https://doi.org/10.1186/s12934-021-01643-x

Copy DOI

Abstract

BackgroundThe aromatic compounds vanillin and vanillic acid are important fragrances used in the food, beverage, cosmetic and pharmaceutical industries. Currently, most aromatic compounds used in products are chemically synthesized, while only a small percentage is extracted from natural sources. The metabolism of vanillin and vanillic acid has been studied for decades in microorganisms and many studies have been conducted that showed that both can be produced from ferulic acid using bacteria. In contrast, the degradation of vanillin and vanillic acid by fungi is poorly studied and no genes involved in this metabolic pathway have been identified. In this study, we aimed to clarify this metabolic pathway in Aspergillus niger and identify the genes involved.ResultsUsing whole-genome transcriptome data, four genes involved in vanillin and vanillic acid metabolism were identified. These include vanillin dehydrogenase (vdhA), vanillic acid hydroxylase (vhyA), and two genes encoding novel enzymes, which function as methoxyhydroquinone 1,2-dioxygenase (mhdA) and 4-oxo-monomethyl adipate esterase (omeA). Deletion of these genes in A. niger confirmed their role in aromatic metabolism and the enzymatic activities of these enzymes were verified. In addition, we demonstrated that mhdA and vhyA deletion mutants can be used as fungal cell factories for the accumulation of vanillic acid and methoxyhydroquinone from guaiacyl lignin units and related aromatic compounds.ConclusionsThis study provides new insights into the fungal aromatic metabolic pathways involved in the degradation of guaiacyl units and related aromatic compounds. The identification of the involved genes unlocks new potential for engineering aromatic compound-producing fungal cell factories.

Highlights

Aromatic compounds, such as vanillin and vanillic acid, are important flavor and fragrance compounds, and are used in the food, beverage, cosmetic and pharmaceutical industries [1,2,3]
Identification of candidate genes encoding putative vanillin dehydrogenase, vanillate hydroxylase, methoxyhydroquinone 1,2‐dioxygenase and 4‐oxo‐monomethyl adipate esterase To identify candidate genes involved in the metabolism of ferulic acid and vanillic acid, whole-genome transcriptome data of A. niger N402 grown on coniferyl alcohol, vanillic acid and veratric acid were generated
Whole-genome transcriptome data from A. niger N402 grown on ferulic acid and no carbon source was obtained from Lubbers et al [25]

Summary

Introduction

Aromatic compounds, such as vanillin and vanillic acid, are important flavor and fragrance compounds, and are used in the food, beverage, cosmetic and pharmaceutical industries [1,2,3]. Less than 1% of the produced vanillin is derived from natural sources, while the majority of vanillin is obtained through chemical synthesis, mainly from guaiacol [1, 7]. In addition to oxidative routes, vanillic acid can be demethylated to protocatechuic acid by vanillate-o-demethylase oxidoreductase or hydroxylated to methoxyhydroquinone by vanillate hydroxylase [15,16,17] The latter appears to be uncommon for bacteria [17]. The aromatic compounds vanillin and vanillic acid are important fragrances used in the food, beverage, cosmetic and pharmaceutical industries. The degradation of vanillin and vanillic acid by fungi is poorly studied and no genes involved in this metabolic pathway have been identified. We aimed to clarify this metabolic pathway in Aspergillus niger and identify the genes involved

Objectives

Methods

Results

Conclusion