Synergistic production and purification of extreme xylanase produced by Aspergillus flavus AUMC 10331 and A. oryzae AUMC 10329 from rice husk in solid-state fermentation

Abstract

Aspergillus flavus AUMC 10331 and A. oryzae AUMC 10329 were used in consortium culture for the production of xylanase enzyme from rice husk using solid-state fermentation technique. The xylanase purification was performed using ion exchange resin IR-120 EP and Sephadex G-75. The purified xylanase showed a total activity of 293.0 IU and a specific activity of 350.96 IU/mg protein and the enzyme was purified to 8.1 fold with 2.7% recovery. The purified xylanase was active over a wide spectrum of pHs from 3-10 and the highest activity was obtained at pH 7.0 followed by 74% of xylanase activity at pH 9.5. At pH 9.5, the xylanase exhibited its optimal activity at 70 °C indicating that the xylanase was alkaliphilic and thermophilic xylanase. The xylanase activity was greatly increased by FeSO4 and CuSO4 up to 332.15% and 194.1% respectively and slightly inhibited by CoCl2. Km and Vmax for the purified xylanase were determined at pH 9.5 and 70 °C for birchwood xylan as 22.13 mg/ml and 135.13 IU/min respectively. The crude and purified enzyme showed high specificity towards the xylans tested. The highest activity was observed for oat spelt xylan; it was three times the activity of birchwood xylan for the crude enzyme and more than six times for the purified enzyme. The specific activity of the xylanase towards birchwood xylan was lower than oat spelt xylan and avicell. The purified xylanase did not act towards carboxymethyl cellulose compared with the crude one.