Recombinant glucoamylase production by Aspergillus niger B1 in chemostat and pH auxostat cultures.
The production of glucoamylase (GAM) by Aspergillus niger B1, a genetic transformant containing an additional 20 copies of the homologous glucoamylase gene (glaA) was studied in nutrient (maltodextrin)-limited chemostat and nutrient-excess pH auxostat cultures. In these culture systems the specific production rate of GAM increased with dilution rate and reached a maximum (up to 15.0 mg GAM [g biomass]-1 h-1) when A. niger B1 was grown at its maximum specific growth rate in pH auxostat culture, indicating that GAM is a growth-associated product. The appearance of spontaneous morphological mutants was observed in all continuous flow cultures grown at pH 5.4, with a light brown mutant always displacing the parental strain. However, no morphological mutants were observed in cultures grown at pH 4.0. Further, when A. niger B1 was grown in pH auxostat culture, the specific production rate of GAM was 31% higher at pH 4.0 than at pH 5.4. Southern blot analyses showed that some morphological mutants (including the light brown mutant) isolated from a pH auxostat culture had lost copies of the glaA genes.
Swift
R J
RJ
School of Biological Sciences, University of Manchester, United Kingdom.
Wiebe
M G
MG
Robson
G D
GD
Trinci
A P
AP
D001234:Aspergillus niger / Q000201:enzymology* / Q000254:growth & development*; D018533:Biomass; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005087:Glucan 1,4-alpha-Glucosidase / Q000096:biosynthesis* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008828:Microbiological Techniques; D011994:Recombinant Proteins / Q000096:biosynthesis