Changes in Reticulitermes flavipes (Kollar) Gut Cellulolytic Activities in Response to Hardwood, Softwood and Cellulose Diets

Abstract

Three cellulase activities (endoglucanase, exoglucanase and β-glucosidase) were assayed for each gut region of field-fed Reticulitermes flavipes (Kollar) workers, in comparison with population subsamples kept in the laboratory on 3 diets: red oak (Quercus spp.), pine (Pinus spp.) and filter paper. The 3 cellulase activities were generally higher in the field-fed termites compared with the 3 subpopulations that were fed on laboratory diets, especially the oak and pine diets. Endoglucanase activity was evenly distributed in the foregut and hindgut with ~36 - 50% of the activity associated with the hindgut. This finding provides good supporting evidence that endoglucanases are produced both endogenously and also by symbionts that enhance cellulose digestion in the hindgut. Exoglucanase activities were mainly located in the hindgut (>87 - 95% of total), suggesting that partially digested cellulose travels from the foregut and midgut to the hindgut where it is exposed to symbiont-derived exoglucanases. β-glucosidase activity was found distributed through all 3 gut regions with ~37 - 56% of the activity found in the hindgut. Cellulolytic activities in R. flavipes can thus change to accommodate dietary composition. One hypothesis is that this change is accomplished via changing hindgut protozoan community composition. However, another equally plausible hypothesis is that endogenous cellulase activities can be altered via differential gene expression in response to changing diet. This flexibility apparently allows R. flavipes to efficiently use a variety of wood and wood-derived materials that contain a variety of lignocellulose compositions.