Enhanced production of calcium citrate by a 2 - deoxy - D - glucose resistant mutant strain of Aspergillus niger using two factorial design

Over hundred isolates of the filamentous fungus Aspergillus niger were examined for calcium citrate productivity under submerged culture conditions in 1-L Erlenmeyer flasks. The isolate IIB-46 was selected for improvement through ultraviolet (UV) light-induced mutagenesis. Among viable mutants, strain 19 exhibited the best citrate productivity, and it was subjected to ethyl methane sulphonate (EMS) treatment. The mutant was cultured overnight and plated on 2-deoxy-D-glucose-PDA medium. A mutant strain EMS-6 gave the highest citrate production (86.48 g/l) which varied significantly (p≤0.05) from that of the wild type. The optimal citrate synthase activity (28 U/ml/min) was achieved at the optimal fermentation conditions with 26.5 g/l DCM. Maximum glucose consumption was found to be 130 g/l (over 90 % substrate conversion rate). Citrate productivity was increased over 28 % when the process parameters, incubation period (72 h), initial pH (6.5), glucose as carbon source (15 %), inoculum size (1.875×10 CFU/ml) and corn steep liquor (CSL) as nitrogen source (0.5 %) were optimized using a 2-factorial Plackett-Burman design. The model terms were highly significant (HS) thus suggesting the potential commercial utility of the mutant (df=3~0.0218). [Sikander Ali and Ikram-ul-Haq. Enhanced production of calcium citrate by a 2-deoxy-D-glucose resistant mutant strain of Aspergillus niger using two factorial design. Nature and Science 2012;10(5):15-22]. (ISSN: 1545-0740). http://www.sciencepub.net/nature. 3