Marked variations in patterns of cellulase activity against crystalline- vs. carboxymethyl-cellulose in the digestive systems of diverse, wood-feeding termites

Throughout the history of studies on cellulose digestion in termites, carboxymethyl-cellulose has been preferably used as a substrate for measuring cellulase activity in termites due to its high solubility. However, carboxymethyl-cellulose degradation is not directly related to digestibility of naturally occurring cellulose because many noncellulolytic organisms can also hydrolyse carboxymethyl-cellulose. To address this issue, a comparative study of microcrystalline cellulose digestion is performed in diverse xylophagous termites, using gut homogenates. For those termites harbouring gut flagellates, the majority of crystalline cellulose appears to be digested in the hindgut, both in the supernatant and the pellet. For Nasutitermes takasagoensis, a termite free of gut flagellates, crystalline cellulose is degraded primarily in the midgut supernatant, and partially in the pellet of the hindgut. The fungus-growing termite Odontotermes formosanus, which also does not possess intestinal flagellates, shows only a trace of crystalline cellulose hydrolysis throughout the gut. Comparison of levels of activity against crystalline cellulose with previously reported levels of activity against carboxymethyl-cellulose in the gut of each termite reveals significant differences between these activities. The results suggest that the hindgut flagellates produce commonly cellobiohydrolases in addition to endo-beta-1,4-glucanases, which presumably act synergistically to digest cellulose. Preliminary evidence for the involvement of bacteria in the cellulose digestion of N. takasagoensis is also found.