Thermostable beta-glucosidase and beta-xylosidase from Thermotoga sp. strain FjSS3-B.1.

A beta-D-glucosidase and a beta-D-xylosidase were purified to homogeneity from the thermophilic eubacterium Thermotoga sp. strain FjSS3-B.1. Both enzymes were largely cell-associated and were probably associated with the 'toga' structures of this organism. Using SDS-PAGE they were found to have M(r) values of 75,000 and 92,000, respectively. The beta-glucosidase was active against cellobiose, sophorose and gentiobiose with Km values of 59 mM, 2.7 mM and 6 mM, respectively. The beta-xylosidase had a Km of 2 mM for xylobiose, showed strong activity against p-nitrophenyl alpha-L-arabinofuranoside and p-nitrophenyl alpha-L-arabinopyranoside, but was subject to strong substrate inhibition by p-nitrophenyl beta-D-xylopyranoside. Both enzymes were extremely thermostable, with half-lives of several hours at 98 degrees C. The thermostabilities of both enzymes were increased further by the addition of either trehalose or betaine.