title: Effect of volume of culture medium on enhanced citric acid productivity by a mutant culture of Aspergillus niger in stirred fermentor.
abstract: OBJECTIVE
  The present study deals with the effect of volume of culture medium on enhanced citric acid productivity by a mutant culture of Aspergillus niger.
  
  
  RESULTS
  A laboratory scale stirred fermentor of 15-l capacity was employed for all microbial cultivations. Blackstrap molasses, a by-product of sugar industries is easily and abundantly available for its exploitation as a carbon source in fermentation processes. The parental culture of A. niger was improved by mutation using ultraviolet radiations and N-methyl N-nitro N-nitroso guanidine, i.e. mutagen MNNG. Six MUV and eight MNNG-treated mutant strains were isolated after extensive screening and optimization. Mutant strain of A. niger MNNG-2 showed enhanced citric productivity (87.60 g l-1) over the parental strain BTL-45 (19.53 g l-1) and other mutant derivatives (49.85 g l-1 citric acid in case of mutant MUV-5 and 76.82 g l-1 in case of mutant MNNG-7). The optimal sugar level was found to be 150 g l-1 (optimum volume of the medium, 60%) after 6 days of inoculation, which is economically significant. Specific productivity of the mutant culture MNNG-2 (qp = 0.057 g/g cells h-1) was several folds higher than other strains.
  
  
  CONCLUSIONS
  The results of the present study are of commercial level. All kinetic parameters including yield coefficients and volumetric rates revealed the hyper-producibility of citric acid by mutant MNNG-2 using blackstrap molasses as the basal medium in stirred fermentor.
authors.affiliation: Department of Botany, Biotechnology Labs, Government College University, Lahore, Pakistan. ikrhaq@yahoo.com
authors.forename: I U
authors.initials: IU
authors.lastname: Haq
authors.forename: S
authors.initials: S
authors.lastname: Ali
authors.forename: J
authors.initials: J
authors.lastname: Iqbal
mesh_terms: D001234:Aspergillus niger / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D019149:Bioreactors; D019343:Citric Acid / Q000302:isolation & purification / Q000378:metabolism*; D003470:Culture Media; D005285:Fermentation; D008769:Methylnitronitrosoguanidine / Q000378:metabolism; D008965:Molasses; D009154:Mutation; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D003470:Culture Media; D008769:Methylnitronitrosoguanidine; D019343:Citric Acid