Marked variations in patterns of cellulase activity against crystalline- vs. carboxymethyl-cellulose in the digestive systems of diverse, wood-feeding termites |
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Authors: | Gaku Tokuda Nathan Lo Hirofumi Watanabe |
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Institution: | Integrative Biology Group, Center of Molecular Biosciences, University of the Ryukyus, Nishihara, Okinawa, Japan,;School of Biological Sciences, The University of Sydney, Sydney, NSW, Australia and;National Institute of Agrobiological Science, Tsukuba, Ibaraki, Japan |
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Abstract: | Abstract. 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-β-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. |
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Keywords: | Cellulase cellulose digestion crystalline cellulose gut salivary glands termites |
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