Effect of digestion by pure cellulases on crystallinity and average chain length for bacterial and microcrystalline celluloses

In this study we employed Size Exclusion Chromatography (SEC) and X-ray diffraction to monitor the molecular weight and crystallinity of bacterial cellulose I and II (BC-I, BC-II) and microcrystalline cellulose (MCC) digested with three "pure" Thermobifida fusca cellulases (Cel6A, Cel6B, and Cel9A). For each enzyme, cellulose crystallinity was found to increase modestly with treatment time. The digestion rate of BC-II was higher than that of BC-I for Cel6A and Cel9A, both endocellulases. SEC results show that the endocellulases create a very rapid decrease in cellulose molecular weight while a slower molecular weight loss was observed with Cel6B, an exocellulase. This work suggests that conversion of native cellulose I to cellulose II by mercerization may beneficially impact the rate of sugar release by cellulases from biomass. In general, lower conversion rates are observed for MCC compared to BC, possibly due to a higher initial crystallinity for MCC. Surface area effects may also be important.