The digestion of bacterial cellulose ribbons by ternary mixtures of enzymes consisting of recombinant cellulases (two cellobiohydrolases, Cel6A and Cel7A, and the endoglucanase Ce145A) from Humicola insolens was investigated over a wide range of mixture composition. The extent of digestion was followed by soluble sugar release (saccharification) analysis together with transmission electron microscopy (TEM) observations. It was found that the addition of minute quantities of Ce145A induced a spectacular increase in saccharification of the substrate with either Cel7A or the mixture of Cel6A and Cel7A. Conversely, only a moderate saccharification resulted from the mixing of Ce145A and Cel6A. This difference is believed to originate from (1) the occasional endo character of Cel6A and (2) the competition of Cel6A and Ce145A for the substrate sites that are sensitive to endo activity. Interestingly, the mixture of enzymes giving rise to the highest saccharification rate did not always correspond to mixtures of enzymes generating the highest synergy. TEM images revealed that the bacterial cellulose ribbons became at the same time cut and narrowed down under the action of an optimized mixture of the three enzymes. (C) 2001 John Wiley & Sons, Inc.