title: Oxalic acid production by citric acid-producing Aspergillus niger overexpressing the oxaloacetate hydrolase gene oahA.
abstract: The filamentous fungus Aspergillus niger is used worldwide in the industrial production of citric acid. However, under specific cultivation conditions, citric acid-producing strains of A. niger accumulate oxalic acid as a by-product. Oxalic acid is used as a chelator, detergent, or tanning agent. Here, we sought to develop oxalic acid hyperproducers using A. niger as a host. To generate oxalic acid hyperproducers by metabolic engineering, transformants overexpressing the oahA gene, encoding oxaloacetate hydrolase (OAH; EC 3.7.1.1), were constructed in citric acid-producing A. niger WU-2223L as a host. The oxalic acid production capacity of this strain was examined by cultivation of EOAH-1 under conditions appropriate for oxalic acid production with 30 g/l glucose as a carbon source. Under all the cultivation conditions tested, the amount of oxalic acid produced by EOAH-1, a representative oahA-overexpressing transformant, exceeded that produced by A. niger WU-2223L. A. niger WU-2223L and EOAH-1 produced 15.6 and 28.9 g/l oxalic acid, respectively, during the 12-day cultivation period. The yield of oxalic acid for EOAH-1 was 64.2 % of the maximum theoretical yield. Our method for oxalic acid production gave the highest yield of any study reported to date. Therefore, we succeeded in generating oxalic acid hyperproducers by overexpressing a single gene, i.e., oahA, in citric acid-producing A. niger as a host.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo, 169-8555, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Takasumi
authors.initials: T
authors.lastname: Hattori
authors.forename: Yuki
authors.initials: Y
authors.lastname: Honda
authors.forename: Kohtaro
authors.initials: K
authors.lastname: Kirimura
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D001234:Aspergillus niger / Q000235:genetics* / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D006867:Hydrolases / Q000235:genetics* / Q000378:metabolism; D060847:Metabolic Engineering; D019815:Oxalic Acid / Q000378:metabolism*
chemical_list: D019343:Citric Acid; D019815:Oxalic Acid; D000445:Aldehyde Oxidoreductases; C040590:glyoxylate dehydrogenase (acylating); D006867:Hydrolases; C054172:oxaloacetase