title: The Effect of organic nitrogen sources on recombinant glucoamylase production by Aspergillus niger in chemostat culture.
abstract: Aspergillus niger B1, a recombinant strain carrying 20 extra copies of the native glucoamylase gene, was grown in glucose-limited chemostat cultures supplemented with various organic nitrogen sources (dilution rate 0.12 +/- 0.01 h(-1), pH 5.4). In cultures supplemented with l-alanine, l-methionine, casamino acids, or peptone, specific glucoamylase (GAM) production rapidly decreased to less than 20% of the initial level. Reducing the pH of the culture to 4.0 resulted in stable GAM production for up to 400 h. Morphological mutants (a light brown and a dark brown mutant) appeared in each fermentation and generally displaced B1. Light brown mutants had higher selection coefficients relative to B1 than dark brown mutants and became the dominant strain in all fermentations except those maintained at pH 4.0. Several mutants isolated from these cultures had reduced ability to produce GAM in batch culture, although few had lost copies of the glaA gene. Some mutants had methylated DNA.
authors.affiliation: School of Biological Sciences, University of Manchester, 1.800 Stopford Building, Manchester, M13 9PL, United Kingdom.
authors.forename: R J
authors.initials: RJ
authors.lastname: Swift
authors.forename: A
authors.initials: A
authors.lastname: Karandikar
authors.forename: A M
authors.initials: AM
authors.lastname: Griffen
authors.forename: P J
authors.initials: PJ
authors.lastname: Punt
authors.forename: C A
authors.initials: CA
authors.lastname: van den Hondel
authors.forename: G D
authors.initials: GD
authors.lastname: Robson
authors.forename: A P
authors.initials: AP
authors.lastname: Trinci
authors.forename: M G
authors.initials: MG
authors.lastname: Wiebe
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D003470:Culture Media; D005087:Glucan 1,4-alpha-Glucosidase / Q000235:genetics* / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism*; D009930:Organic Chemicals; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D009930:Organic Chemicals; D011994:Recombinant Proteins; D005087:Glucan 1,4-alpha-Glucosidase; D005947:Glucose; D009584:Nitrogen