Clostridium thermocellum displays the ability to produce plant cell wall degrading enzymes and ferment the resulting sugars to ethanol and other products.  C. thermocellum utilizes cellulosomes to degrade biomass and genomic studies have confirmed that this organism produces no exocellulases from glycosyl hyrolase families 6 or 7.  The only enzymes confirmed to be exoglucanses in this system are from GH family 48, although several members of GH family 9, thought to be processive endoglucanases, probably assist the GH48 enzymes in hydrolyzing crystalline cellulose.  Therefore, the deconstruction of cellulose depends heavily upon the action of the GH48 enzymes, which are produced by C. thermocellum in both a cellulosomal (GH48; contains a dockerin domain) and non cellulosomal (CelY; contains a CBD domain) configuration.  We are building a library of GH48 enzymes from a diversity of sources for biochemical characterization and activity testing.  We will report results from initial studies of available enzymes using both wild type and chimeric constructs.  Understanding the mechanism of action of these enzymes is critical to the challenge of improving the wild type performance of this microbial cellulose degrader.