CHAPTER # 1: LITERATURE REVIEW Gardnerj et al (1956) investigated citric acid production by mutants of Aspergillus niger. The strain of Aspergillus niger was improved by X-rays and ultraviolet irradiations and found that as compared to wild, the mutated strain give more yield of citric acid. They concluded that 80 % of the sugar fermented was obtained in aerated culture, whereas only 21 % was obtained with the parent strain. Banik et al