PRODUCTION AND CHARACTERIZATION OF THERMOSTABLE XYLANASES BY THERMOMYCES-LANUGINOSUS AND THERMOASCUS-AURANTIACUS GROWN ON LIGNOCELLULOSES

Thermomyces lanuginosus and Thermoascus aurantiacus isolated from self-heated jute fiber stalk were studied for xylanase production using various lignocelluloses under solid-state fermentation. Both organisms performed creditably well with unsupplemented wheat bran at 55 degrees C. T. lanuginosus produced cellulase-free xylanase, whereas T. aurantiacus produced a small amount of cellulase in addition. Xylan (0.7%) also induced xylanase production in T. lanuginosus, leading to a 28.0% increase. The effect of initial moisture level was optimized for the fungi. T. lanuginosus and T. aurantiacus performed best at 80 and 50% initial moisture, respectively. Characterization of the enzymes reveals that xylanases from T. lanuginosus and T. aurantiacus were most active at 70 degrees C, but at pH 6.0 and 5.0, respectively. Both xylanases displayed remarkable pH (5.0 to 11.0) and thermal stabilities by retaining most of their activities even after having been subjected to temperatures much higher than their optimal. Furthermore, they remained active under prolonged storage, having no loss of activity after 1 month of storage at 4 degrees C and retaining up to about 90% after 10 days at 55 degrees C. Xylanase from T. lanuginosus was better and produced a softer and mechanically stronger final product than that from T. aurantiacus when both were applied to low-quality jute fiber. The findings in this study have great implications for the future applications of xylanase.