ABSTRACT
The xylanolytic potential of thermophilic molds has attracted interest for decades because of their pivotal role in composting and degradation of agro-residues, mushroom production, and solid waste management. A spurt of interest in these enzymes in recent years is due to their application in various industrial sectors like, paper and pulp, animalfeed, food, wine, textile, and pharmaceuticals (Kuhad et al. 1997). Thus, their biotechnological applications would help in fulfilling the increased demand of food and fuel for the staggerdly and nonexponentially increasing population world-wide, besides, resulting in economically viable and eco-friendly technologies. Xylanase hydrolyses β1,4 glycosidic linkages between D-xylanopyranose units of xylan, a heteropolysaccharide with substitutions like, acetylation at the C-2 or C-3 of the xylose units; α-1,2-linked glucuronic or 4-O-methylglucuronic acid groups; α-1,3-linked arabinofuranose units and ferulic or coumaric acids esterified to C-5 of arabinose (Coughlan 1992). Xylan, is a heterogeneous substrate that requires synergistic action of main-chain and side-chain cleaving enzymes for complete hydrolysis. The main-chain cleaving enzymes include: endo-xylanase (β-1,4-D-xylan xylanohydrolase, E.C.3.2.1.8), which is well characterised in Chaetomium thermophile, Humicola grisea, and Talaromyces emersonii (Ganju et al. 1989; Thakur et al. 1992; Tuohy et al. 1993); exoxylanase (β-1,4-Dxylan xylanohydrolase), whose existence has been reported in some thermophilic molds like, Chaetomium thermophile (Ganju et al. 1989), but is not a well-studied enzyme, and βxylosidase (β-1,4-D-xylan xylanohydrolase, E.C.3.2.1.37), produced in appreciable amounts by Aspergillus fumigatus, Humicola lanuginosa, and T. emersonii (Anand and Vithayathil 1996; Kitpreechavanich 1984; Tuohy et al. 1993). The side-chain enzymes act cooperatively by removing side chain substituents prior to depolymerisation of the high molecular weight backbone by the main chain cleaving enzymes. These enzymes include: α-L-arabinofuranosidase (AF) (E.C. 3.2.1.55), well characterised in Rhizomucor pusillus and T. emersonii (Rahman et al. 2001; Tuohy et al. 1993); acetyl (xylan) esterase (E.C. 3.1.1.6), reported in Melanocarpus albomyces (Jain 1995) and α-D-glucuronidase (E.C. 3.2.1??), which is characterised in Thennoascus aurantiacus (Khandke et al. 1989c).
