An artificial, bifunctional, thermostable cellulase-xylanase enzyme from Thermotoga maritima by gene fusion. The fusion protein exhibited both cellulase and xylanase activity when xynA was fused downstream of cel5C but no activities were shown when xynA was fused upstream of cel5C. The enzyme was optimally active at pH 5.0 and 80 degrees C over 30 min. E. coli expressed the fusion enzyme, with an apparent molecular mass of approximately 152 kDa by carboxymethyl cellulose- and xylan-SDS-PAGE.