Enhanced xylanase production from UV-mutated Aspergillus niger grown on corn cob and sawdust

This study investigated the production and characterization of xylanase from wild-type and UV-mutated Aspergillus niger, grown on corn cob and sawdust. Three fungal isolates: Aspergillus niger, Aspergillus flavus and Aspergillus fumigatus isolated from soil were screened for xylanase production and identified based on their morphological and molecular characteristics. The effects of cultural conditions (pH, temperature, nitrogen sources, carbon sources and metal ions) on the production of xylanase by the selected isolate were investigated for both the wild-type and the UV-mutated strains. Based on the zone of clearance and xylanase production in submerged fermentation, Aspergillus niger gave the highest yield out of the three isolates. The optimum pH and temperature for the production of xylanase by wild-type and UV-mutated strains were pH 5.0 and 25 °C, respectively. Corn cob and ammonium sulphate were the optimum carbon and nitrogen sources, respectively. Mn²⁺ enhanced the production of xylanase with both the wild-type and UV-mutated A. niger whereas Cu²⁺ inhibited the enzyme production. The xylanases from the wild-type and UV-mutated strains were partially purified using ammonium sulphate precipitation. The optimum temperature and pH for the activity of the partially purified xylanase were 45 °C and pH 3.0, respectively. The xylanases were most stable at pH 3.0 and temperature of 45 °C. Corn cob increased the activity of the enzyme than sawdust when used as substrate. The result obtained from this study showed a maximum xylanase activity of 9.3641 U/mL with the UV-mutated A. niger strain, which was higher than the maximum xylanase activity of 4.124 U/mL obtained with the wild-type. This shows that UV-mutagenesis of A. niger strain used in this study resulted in better yield of xylanase. The use of corncob and sawdust as substrates for xylanase production offers both environmental and economic advantages as it would decrease the amount of these wastes in the environment as well as reduce the cost of xylanase production.