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CONTROL OF ASPERGILLUS NIGER MORPHOLOGY TO ENHANCE CITRIC ACID PRODUCTION UNDER LIQUID CULTURE

IKRAM-UL-HAQ, SIKANDER ALI, M.A. QADEER AND *JAVED IQBAL

Abstract: The present investigation deals with the control of Aspergillus niger morphology to enhance citric acid production under liquid culture. For this purpose, the parental Aspergillus niger GCB-16 and its mutant derivative NG-101 were mutually compared, using 150 g/l carbohydrates of cane-molasses as the basal fermentation medium. The mutant showed a 1.26 fold increase in citric acid production over the control as compared to 2.82 in times the wild-type culture. Addition of 2.0 x 10^-5M CuSO₄ to the fermentation medium reduced the Fe⁺² ion concentration by counteracting its deleterious effect on fungal growth. The copper ion also induced a loose-pelleted form of growth (0.5 mm, dia.), reduced the biomass concentration (12.5 g/l) and increased the volumetric productivity of citric acid monohydrate (93.6±5 g/l). On the basis of comparison of kinetic parameters viz., the volumetric substrate uptake rate (Qs) and specific uptake rate (qs), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutant was faster growing organism (Yx/s = 0.118±0.02 g/g) and had the ability to overproduce citric acid (Yp/s = 0.340±0.02 g/g).

Biotechnology Research Laboratories, Department of Botany, Govt. College Univ., Lahore, Pakistan.
Department of Botany, Quaid-e-Azam Campus, University of the Punjab, Lahore, Pakistan.