title: Metabolic engineering of fungal strains for conversion of D-galacturonate to meso-galactarate.
abstract: D-galacturonic acid can be obtained by hydrolyzing pectin, which is an abundant and low value raw material. By means of metabolic engineering, we constructed fungal strains for the conversion of D-galacturonate to meso-galactarate (mucate). Galactarate has applications in food, cosmetics, and pharmaceuticals and as a platform chemical. In fungi D-galacturonate is catabolized through a reductive pathway with a D-galacturonate reductase as the first enzyme. Deleting the corresponding gene in the fungi Hypocrea jecorina and Aspergillus niger resulted in strains unable to grow on D-galacturonate. The genes of the pathway for D-galacturonate catabolism were upregulated in the presence of D-galacturonate in A. niger, even when the gene for D-galacturonate reductase was deleted, indicating that D-galacturonate itself is an inducer for the pathway. A bacterial gene coding for a D-galacturonate dehydrogenase catalyzing the NAD-dependent oxidation of D-galacturonate to galactarate was introduced to both strains with disrupted D-galacturonate catabolism. Both strains converted D-galacturonate to galactarate. The resulting H. jecorina strain produced galactarate at high yield. The A. niger strain regained the ability to grow on d-galacturonate when the D-galacturonate dehydrogenase was introduced, suggesting that it has a pathway for galactarate catabolism.
authors.affiliation: VTT Technical Research Centre of Finland, Tietotie 2, Espoo, P.O. Box 1500, 02044 VTT, Finland.
authors.forename: Dominik
authors.initials: D
authors.lastname: Mojzita
authors.forename: Marilyn
authors.initials: M
authors.lastname: Wiebe
authors.forename: Satu
authors.initials: S
authors.lastname: Hilditch
authors.forename: Harry
authors.initials: H
authors.lastname: Boer
authors.forename: Merja
authors.initials: M
authors.lastname: Penttilä
authors.forename: Peter
authors.initials: P
authors.lastname: Richard
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D001711:Biotransformation; D017353:Gene Deletion; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005818:Genetic Engineering; D006603:Hexuronic Acids / Q000378:metabolism*; D035901:Hypocrea / Q000201:enzymology* / Q000235:genetics; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D011995:Recombination, Genetic; D013400:Sugar Acids / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D006603:Hexuronic Acids; D013400:Sugar Acids; C007819:galacturonic acid; C000090:galactaric acid