Effect of chemical nutrients on aconitase activity during citric acid fermentation by a mutant strain of Aspergillus niger.

An ethyleneimine and UV irradiated mutant strain Aspergillus niger AB 1801 was explored for its aconitase activity, citric acid production and cell growth during citric acid fermentation. 10% sucrose and 0.25% urea served as the best carbon and nitrogen sources, respectively. Fe2+ stimulated aconitase activity and Co2+ (upto 5 micrograms/mL) and Ni2+ (10 micrograms/mL) strongly depressed enzyme activity. Boric acid (0.5 mg/L) had very good stimulatory response towards citric acid production. Aconitase activity has been found to vary inversely with the citric acid production upto a certain limit after which the activity was absent in the mycelial extract. Cell growth varied with the production parameter.