A Dictyoglomus turgidum thermostable cellulase enzyme with both endocellulase activity and exocellulase activity that is able to degrade cellulose in the absence of scaffoldins and other cellulosomic proteins is provided. The use of the enzyme to degrade cellulosic materials to soluble sugars is also provided. Also described are nucleic acid constructs that encode and express the cellulase, and hosts transformed to contain the nucleic acid constructs.