Characteristics of thermostable endoxylanase and β-xylosidase of the extremely thermophilic bacterium Geobacillus thermodenitrificans TSAA1 and its applicability in generating xylooligosaccharides and xylose from agro-residues

An extremely thermophilic bacterial isolate that produces a high titer of thermostable endoxylanase and beta-xylosidase extracellularly in an inducible manner was identified as Geobacillus thermodenitrificans TSAA1. The distinctive features of this strain are alkalitolerance and halotolerance. The endoxylanase is active over a broad range of pH (5.0-10.0) and temperatures (30-100 A degrees C) with optima at pH 7.5 and 70 A degrees C, while beta-xylosidase is optimally active at pH 7.0 and 60 A degrees C. The T (1/2) values of the endoxylanase and beta-xylosidase are 30 min at 80 A degrees C, and 180 min at 70 A degrees C, respectively. The endoxylanase activity is stimulated by dithiothreitol, but inhibited strongly by EDAC and Woodward's reagent K. N-BS and DEPC strongly inhibited beta-xylosidase. MALDI-ToF (MS/MS) analysis of tryptic digest of beta-xylosidase revealed similarity with that of G. thermodenitrificans NG 80-2, and suggested that this belongs to the GH 52 glycosyl hydrolase super family. The action of endoxylanase on birch wood xylan and agro-residues such as wheat bran and wheat straw liberated xylooligosaccharides similar to endoxylanases of the family 10 glycoside hydrolases, while the enzyme preparation having both endoxylanase and beta-xylosidase liberated xylose as main hydrolysis product.