GENETIC VARIABILITY AMONG Aspergillus niger AND REGULATION OF CITRIC ACID PRODUCTION

ABSTRACT

Aspergillus niger popularly known as industrial workhorse due to its fitness for industrial fermentation, has the potentials to secret citric acid. The black mould Aspergillus niger has been used in a number of scientific and industrial applications since 1919.Citric acid is one of the major constituent in food, beverages and pharmaceutical. Microbial fermentation with A. niger stains have been used as one of the best methods for producing citric acid compared to chemical processes. In view of surges in demand and growing markets for citric acid, the major attempt in this work was to determine how the product titres can be maximized. A. niger strains were isolated from various food substances. These strains were exposed to UV radiation at 356nm followed by subsequent subjection of the mutant strains to potato dextrose agar amended with chlorate (mutagen). The mutant strains from the chlorate medium were further subjected to another round of mutation using the medium containing chlorate for the second time. Thus, mutation proceeded from UV-PDC1-PDC2. These mutant strains (UV-mutants, PDC1-mutant and PDC2-mutants) with the wild strains as control, were then employed in submerged fermentation for the production of citric acid. The product titres of all the citric acids produced were analyzed. The importance of UV-irradiation (356 nm) in boosting the production of citric acid in A. niger has been highlighted in this study. UV mutation proved to be very significant in preparing the fungus for a higher production of citric acid. The effect of repeated mutations showed that the citric acid production can be genetically regulated. Thus the ability to engineer the genes encoding the morphological variation or the constitutive expression of the genes encoding the citric acid may increase the level of citric acid production to the maximum.