The endoglucanase (E1) from Acidothermus cellutolyticus has been used extensively in cellulase research. The goal of this work was to produce high levels of this enzyme in a system that facilitates purification. A codon-optimized synthetic gene for A. cellulolyticus E1 with a C-terminal histidine tag was cloned into the genome of Pichia pastoris. Strain KM71H expressed the most enzyme, with a yield of 550 mg/L culture supernatant. The temperature optimum (80 degrees C) and pH optimum (5.1) of the purified enzyme agree with previously determined values for the enzyme produced in other systems. Michaelis-Menten kinetic parameters were determined, using a fluorescent substrate (methylumbelliferyl-beta-D-cellobioside) at various temperatures. This thermostable enzyme can be used in future cellulosic biofuels-related research. (c) 2011 Elsevier Inc. All rights reserved.