Vanillin dehydrogenase (VhdA) from Aspergillus niger is active on depolymerized lignin

Abstract

Vanillin dehydrogenases are important enzymes involved in the conversion of lignin-derived aromatic aldehydes such as vanillin and p-hydroxybenzaldehyde into its acid form. In a previous study we identified the first fungal vanillin dehydrogenase (VdhA) from the filamentous fungus Aspergillus niger. In this study we heterologous produced VdhA in a bioreactor to obtain sufficient enzyme for a more details analysis of its biochemical properties. This demonstrated that VdhA has a high optimal temperature (50 °C), neutral optimum pH and a broad substrate specificity for aromatic aldehydes. Deletion of vdhA in A. niger resulted in reduced growth on several aromatic aldehydes, largely collating with the in vitro substrate specificity of the enzyme. In addition, we demonstrated that VdhA can convert multiple aromatic aldehydes present in depolymerized lignin, indicating that VdhA can be applied in industrial conversion of lignin fractions to either simplify the composition of the fraction or to reduce the aldehydes that can undergo undesired repolymerization reactions within the mixture.