Thermostable Cellulase and Xylanase from Thermoascus aurantiacus and Their Potential Industrial Applications

Abstract

Thermostable cellulase and xylanase have potential applications in food, animal feed and chemical industries. A major endoglucanase (Endo-I), a major β-glucosidase (β-Glu-I), two major exoglucanases (Exo-HA and Exo-LA) and a major xylanase (Xln-I) were purified and characterised from the thermophilic fungus, Thermoascus aurantiacus. Endo-I, Exo-HA and Exo-LA were optimally active at 70°C, at pH 3.5 and between pH 4.4-5.2 respectively, whereas β-Glu-I and Xln-I showed optimal activity at 80°C and between pH 4.0-5.0. All five enzymes showed remarkable stability up to 60°C and between pH 4.0-6.0 for several hours. β-Glu-I was specific for β-linked glycosides, disaccharides and oligosaccharides. The Endo-I, Exo-HA and Exo-LA were specific for oligosaccharides and polysaccharides with β(1→4) glycosidic bonds. The Xln-I showed higher affinity towards substituted xylans and was active towards xylo-oligosaccharides (Xyln). β-Glu-I cleaved one glucose unit at a time from the non-reducing end of 4-nitrophenyl cello-oligosaccharides (4-NPGlcn). Endo-I hydrolysed Glcn, 4-methylumbelliferyl cello-oligosaccharides (MeUmbGlcn), carboxymethyl cellulose (CM-cellulose) and H3PO4-swollen cellulose in a random fashion. The Exo-HA and Exo-LA preferentially attacked the second glycosidic bond adjacent to 4-methylumbelliferone (MeUmb) of MeUmbGlcn. Xln-I cleaved xylans and Xyln in an endo-fashion. β-Glu-I and Xln-I from T. aurantiacus catalysed the synthesis of various alkyl- and aryl-glycosides. These results and the potential industrial applications of all five enzymes from T. aurantiacus are discussed.