The beta-xylosidase encoding gene (XsidB) of the extremely thermophilic bacterium Geobacillus thermodenitrificans has been cloned and expressed in Escherichia coli. The homotrimeric recombinant XsidB is of 204.0 kDa, which is optimally active at 60 degrees C and pH 7.0 with T-1/2 of 58 min at 70 degrees C. The beta-xylosidase remains unaffected in the presence of most metal ions and organic solvents. The K-m [p-nitrophenyl beta-xyloside (pNPX)], V-max and k(cat) values of the enzyme are 2 x 10 (3) M, 1250 mu moles mg (1) min (1) and 13.20 x 10(5) min (1), respectively. The enzyme catalyzes transxylosylation reactions in the presence of alcohols as acceptors. The pharmaceutically important beta-methyl-D-xylosides could be produced using pNPX as the donor and methanol as acceptor. The products of transxylosylation were identified by TLC and HPLC, and the structure was confirmed by H-1 NMR analysis. The enzyme is also useful in synthesizing transxylosylation products from the wheat bran hydrolysate. (C) 2014 Elsevier Ltd. All rights reserved.