Regulation of Cellulase Synthesis in Acidothermus Cellulolyticus

The regulation of cellulase synthesis by induction and catabolite repression in the thermophilic, aerobic bacterium Acidothermus cellulolyticus was studied in batch fermentations. Various compounds, such as L‐sorbose, cyclic AMP (cAMP), L‐glucose, 2‐deoxyglucose (2‐DG), glucose 1‐phosphate (G‐1‐P), sophorose, salicin, sugar alcohols, and isopropyl thioglucoside (IPTGlu), were added along with Solka Floe to improve extracellular cellulase formation by the culture. When cAMP was added exogenously to A. cellulolyticus cultures in the concentration range of 0.01‐0.2 g/L, cAMP did not affect cell growth; however, cellulase yields were increased with increasing levels of cAMP. The enzyme production rates with the different levels of cAMP addition during Solka‐Floc fermentations were identical. L‐Sorbose, L‐glucose, 2‐DG, G‐1‐P, sophorose, IPTGlu, and sugar alcohols enhanced cellulase activity produced in the medium, but the starting time and the time required to reach the maximum enzyme activity were different in each condition. All these substances may function as moderators of cellulase synthesis. From the experimental results, only cellobiose, xylose, sophorose, and unknown soluble derivatives from cellulose were considered as inducers. In a possible regulatory mechanism of cellulase synthesis, the repressor, inducer, cAMP, and moderator may be all involved in controlling the rate and the yield of enzyme production.