Cellulolytic enzyme components of the cellulase complex of Clostridium thermocellum

Abstract The anaerobic thermophilic cellulolytic bacterium C. thermocellum synthesises and secretes a highly effective cellulase system with the ability to saccharify completely native and derived forms of cellulose. The enzyme complex is strongly adsorbed to carbohydrate matrices, from which it is released with difficulty and in low yield. Non-carbohydrate separation media proved more successful in permitting the isolation of a number of cellulolytic components. Three such enzymic components were recognised in the extracellular medium of the organism. All three enzymes had CM-cellulase activity, but only two were stable to further purification. Of the latter, endoglucanase 1 had considerable quantitative significance in accounting for almost half of the CM-cellulase activity of the culture filtrate, and was highly effective against soluble cellulose derivatives, particularly in reducing the viscosity, but was inactive against cellulose itself. In contrast, endoglucanase 2 acted weakly on CM-cellulase and more effectively against cellulose, from which soluble cellodextrins, but never glucose, were formed. The properties of endoglucanases 1 and 2 suggest they act in a complementary manner to degrade the less crystalline regions of cellulosic materials, thereby providing a rapid and early supply of soluble metabolisable sugars.