title: C- and N-catabolic utilization of tricarboxylic acid cycle-related amino acids by Scheffersomyces stipitis and other yeasts.
abstract: Scheffersomyces stipitis and the closely related yeast Candida shehatae assimilated the L-amino acids glutamate, aspartate and proline as both carbon and nitrogen sole sources. We also found this rarely investigated ability in ascomycetous species such as Candida glabrata, C. reukaufii, C. utilis, Debaryomyces hansenii, Kluyveromyces lactis, K. marxianus, Candida albicans, L. elongisporus, Meyerozyma guilliermondii, C. maltosa, Pichia capsulata and Yarrowia lipolytica and in basidiomycetous species such as Rhodotorula rubra and Trichosporon beigelii. Glutamate was a very efficient carbon source for Sc. stipitis, which enabled a high biomass yield/mole, although the growth rate was lower when compared to growth on glucose medium. The cells secreted waste ammonium during growth on glutamate alone. In Sc. stipitis cultures grown in glucose medium containing glutamate as the nitrogen source the biomass yield was maximal, and ethanol concentration and specific ethanol formation rate were significantly higher than in glucose medium containing ammonium as the nitrogen source. Mainly C-assimilation of glutamate but also N-assimilation in glucose-containing medium correlated with enhanced activity of the NAD-dependent glutamate dehydrogenase 2 (GDH2). A Δgdh2 disruptant was unable to utilize glutamate as either a carbon or a nitrogen source; moreover, this disruptant was also unable to utilize aspartate as a carbon source. The mutation was complemented by retransformation of the GDH2 ORF into the Δgdh2 strain. The results show that Gdh2p plays a dual role in Sc. stipitis as both C- and N-catabolic enzyme, which indicates its role as an interface between the carbon and nitrogen metabolism of this yeast.
authors.affiliation: Department of Biology IV (Microbiology und Genetics), Unit of Applied Microbiology, RWTH Aachen University, Germany. Stefan.Freese@vtt.fi
authors.forename: Stefan
authors.initials: S
authors.lastname: Freese
authors.forename: Tanja
authors.initials: T
authors.lastname: Vogts
authors.forename: Falk
authors.initials: F
authors.lastname: Speer
authors.forename: Bernd
authors.initials: B
authors.lastname: Schäfer
authors.forename: Volkmar
authors.initials: V
authors.lastname: Passoth
authors.forename: Ulrich
authors.initials: U
authors.lastname: Klinner
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D018533:Biomass; D002952:Citric Acid Cycle; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005969:Glutamate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D007218:Industrial Microbiology / Q000379:methods; D003904:Mitosporic Fungi / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D016133:Polymerase Chain Reaction; D011392:Proline / Q000378:metabolism; D014170:Transformation, Genetic
chemical_list: D000596:Amino Acids; D004271:DNA, Fungal; D001224:Aspartic Acid; D000431:Ethanol; D018698:Glutamic Acid; D011392:Proline; D005969:Glutamate Dehydrogenase