The thermostable beta-xylosidase from Sulfolobus solfataricus, expressed in Escherichia coli, was immobilized by entrapment into alginate with full recovery of activity and tested for xylose production from xylan hydrolysates. Since the recombinant activity was also cell bound, alginate beads entrapping E. coli whole cells were also prepared. The immobilized preparations exhibited higher thermostability at 90 degrees C compared to their free counterparts. The half-lives of the immobilized enzyme and cells were 21 and 23 h, respectively, while half of the inactivation was reached after 10 and 11.5 h for free enzyme and whole cells. Interestingly, thermophilicity increased from 85 up to 100 degrees C and the optimal pH shifted to higher values for immobilized preparations. Results obtained from xylo-oligosaccharides hydrolysis in subsequent batch experiments of recycling, indicated-that the immobilized enzyme had good operational stability, retaining 84% of its initial activity after four cycles. Here we report on the immobilization of the beta-xylosidase into alginate and its characterization. (c) 2006 Elsevier Inc. All rights reserved.