Identification of the galactitol dehydrogenase, LadB, that is part of the oxido-reductive D-galactose catabolic pathway in Aspergillus niger

Dominik Mojzita, Outi M. Koivistoinen, Hannu Maaheimo, Merja Penttila, Laura Ruohonen, Peter Richard*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review


For the catabolism of D-galactose three different metabolic pathways have been described in filamentous fungi. Apart from the Leloir pathway and the oxidative pathway, there is an alternative oxido-reductive pathway. This oxido-reductive pathway has similarities to the metabolic pathway of L-arabinose, and in Trichoderma reesei (Hypocrea jecorina) and Aspergillus nidulans the same enzyme is employed for the oxidation of L-arabitol and galactitol. Here we show evidence that in Aspergillus niger L-arabitol dehydrogenase (LadA) is not involved in the D-galactose metabolism; instead another dehydrogenase encoding gene, ladB, is induced in response to D-galactose and galactitol and functions as a galactitol dehydrogenase. Deletion of ladB in A. niger results in growth arrest on galactitol and significantly slower growth on D-galactose supplemented with a small amount of D-xylose. D-galactose alone cannot be utilised by A. niger and the addition of D-xylose stimulates growth on D-galactose via transcriptional activation of the D-xylose-inducible reductase gene, xyrA. XyrA catalyses the first step of the D-galactose oxido-reductive pathway, the reduction to galactitol, which in turn seems to be an inducer of the downstream genes such as LadB. The deletion of xyrA results in reduced growth on D-galactose. The ladB gene was expressed in the heterologous host Saccharomyces cerevisiae and the tagged and purified enzyme characterised. LadB and LadA have similar in vitro activity with galactitol. It was confirmed that the reaction product of the LadB reaction from galactitol is L-xylo-3-hexulose as in the case of the T. reesei Lad1. (C) 2011 Elsevier Inc. All rights reserved.

Original languageEnglish
Pages (from-to)152-159
Number of pages8
JournalFungal Genetics and Biology
Issue number2
Publication statusPublished - Feb 2012
MoE publication typeA1 Journal article-refereed


  • Aspergillus niger
  • D-Galactose
  • Galactitol
  • D-Galactose metabolism
  • Galactitol dehydrogenase
  • L-Arabitol dehydrogenase
  • L-Xylo-3-hexulose
  • GENE

Cite this