Investigation of stress tolerance of endoglucanases of the cellulosomes of Clostridium cellulolyticum to ethanol
Current energy and environmental challenges are driving the use of cellulosic materials for biofuel production. A major obstacle in this pursuit is poor ethanol tolerance among cellulolytic Clostridium species. The objective of this work was to establish a potential upper boundary of ethanol tolerance for the cellulosome itself. The hydrolytic function of crude cellulosome extracts from Clostridium cellulolyticum on carboxymethyl cellulose (CMC) with 0, 5, 10, 15, 20 and 25% ethanol was determined. Results indicate that the endoglucanase activity of the cellulosome incubated in 5 and 10% ethanol was significantly different from a control without ethanol addition. Furthermore the endoglucanase activity for the cellulosomes incubated in 5, 10, 15, 20 and 25% ethanol in a standalone experiment was significantly different from the control without ethanol. Endoglucanase activity continued to be observed for up to 25% ethanol, indicating that cellulosome function in ethanol will not be an impediment to future efforts towards engineering increasing production titers to levels at least as high as the current physiological limits of the most tolerant ethanologenic microbes.
Keywords: Ethanol, Clostridium cellulolyticum carboxymethyl cellulose, endoglucanase activity, cellulosome.