Enzymatic hydrolysis of bacterial cellulose

Abstract

Native cellulose from the bacterium Acetobacter xylinum as well as acid-treated bacterial cellulose prepared from partial hydrolysis of the native bacterial cellulose with 2.5 N HCl were subjected to enzymatic hydrolysis by Trichoderma viride cellobiohydrolase I (CBH I) and endoglucanase II (EG II). The activities of the two enzymes were continuously monitored with an oxidation-reduction potential electrode based on the cellobiose dehydrogenase-ferricyanide redox system. The individual CBH I and EG II hydrolyzed both native and acid-treated bacterial celluloses in a similar way. While CBH I rapidly hydrolyzed both cellulose samples, the ability of EG II to hydrolyze these samples was very limited. However, the hydrolytic behavior of the two cellulose samples by the combination of the two enzymes was significantly different. The rate of hydrolysis of the native bacterial cellulose increased drastically with the combination of the two enzymes, while no synergistic increase in hydrolysis rate was observed with the acid-treated cellulose. Electron microscopy demonstrated that the synergistic action of CBH I and EG II for the native bacterial cellulose involved drastic disintegration of the twisted and bent ribbon-like structure of microfibril bundles and gave rise to the formation of linear, needle-like microcrystallites. Thus, the ribbon-like structure of microfibril bundles in the native bacterial cellulose seems to have a high susceptibility for the combined action of the two enzymes. In contrast, the microfibril aggregates of the acid-treated bacterial cellulose were not disintegrated by the combination of the two enzymes. From these observations, it seems reasonable to assume that differences in the assembling pattern of the microfibrils must be one of the major reasons for the significant differences in the synergism of the two enzymes for the two bacterial cellulose samples. The assembling pattern of microfibrils must be one of the major reasons for the significant synergism of CBH I and EG II for the native bacterial cellulose.