Inducing effects of cellulosic hydrolysate components of lignocellulose on cellulosome synthesis in Clostridium thermocellum

Cellulosome is a highly efficient supramolecular machine for lignocellulose degradation, and its substrate-coupled regulation requires soluble transmembrane signals. However, the inducers for cellulosome synthesis and the inducing effect have not been clarified quantitatively. Values of cellulosome production capacity (CPC) and estimated specific activity (eSA) were calculated based on the primary scaffoldin ScaA to define the stimulating effects on the cellulosome synthesis in terms of quantity and quality respectively. The estimated cellulosome production of Clostridium thermocellum on glucose was at a low housekeeping level. Both Avicel and cellobiose increased CPCs of the cells instead of the eSAs of the cellulosome. The CPC of Avicel-grown cells was over 20-fold of that of glucose-grown cells, while both Avicel- and glucose-derived cellulosomes showed similar eSA. The CPC of cellobiose-grown cells was also over three times higher than glucose-grown cells, but the eSA of cellobiose-derived cellulosome was 16% lower than that of the glucose-derived cellulosome. Our results indicated that cello-oligosaccharides played the key roles in inducing the synthesis of the cellulosome, but non-cellulosic polysaccharides showed no inducing effects.