Effect of Gamma Irradiation on Aspergillus Niger for Enhanced Production of Glucose Oxidase

Developing countries have a high prevalence of diabetes and their populations are suffering from associated adverse factors. Such a frequency requires more effective diagnosis, mostly achieved by glucose diagnostic kits. Although high priced kits are available in market but local production of such kits can be highly cost effective and may confer the decline in incidence of the disease. Glucose oxidase is the key enzyme for the determination of glucose in such analytical tools. Enhanced production of glucose oxidase was performed by mutagenesis of Aspergillus niger by gamma irradiation. A dose of 80krad was found as optimum for derivation of positive mutant strains. Following the screening by triton X-100 and 2deoxy-D-glucose, the selected strains A. niger G-80-A, A. niger G-80-B and A. niger G-80-C showed 27.5, 23.20 and 20.55 UmL glucose oxidase activity in enzyme diffusion zone test; which is much higher to parental strain (7.5 UmL). A. niger G-80-A was subjected to submerged fermentation and obtained highest yields after 36 h, at CSL 2%, pH 6.5, 30°C, KH2PO40.8% and urea 0.3%. Partial purification by ammonium sulfate resulted in 175UmL of glucose oxidase activity after dialysis. Kinetic parameters like optimum pH, temperature, Km and Vmax were found to be 6.0 (180±2 UmL), 30°C (185±0.5 UmL), 5.26mM and 400U mL, respectively. Active inhibition of the enzyme by increasing concentration of PLP in reaction mixture confirmed the presence of functional lysyl residue on the active site of enzyme.