Primary Studies On The Activities Of Cellulases In Four Different Termite Species

Cellulose is the most abundant natural resource on Earth. As one of the most efficient cellulose decomposers in the nature, termites are becoming more and more attractive for scientists for their capabilities to degrade cellulose and potential application in the new biomass energy industry. It has been reported that termites degrade cellulose by the use of both cellulases secreted by themselves and the cellulases originated from their gut symbiotic microbes. The cellulases involved in the cellulose degradation include endo-β-1,4-glucanase(EG),β-1,4-glucosidase(BG), and exo-β-1,4-glucanase or cellobiohydrolase (CBH). However, the mechanism of cellulose degradation of termites are still not clear.To illuminate the mechanism of cellulose degradation of different types of termites, cellulase activities of four different termite species Reticulitermes chinensis Snyder, Macrotermes barneyi Light, Nasutitermes sp., and Microcerotermes sp. and their different gut segments were studied with DNS assay. In addition, the diversity and distribution of endo-β-1,4-glucanase in different gut segments of the four termites were analyzed with Native-PAGE electrophoreses. The results showed that endo- β-1,4-glucanase has the highest enzyme activities among the three cellulases in the four studied termites. DNS assay with the crude enzyme extract obtained from the four termites showed that the optimum reaction substrate concentration for the three cellulases was 1% and the optimum reaction pH for the three cellulases was 5.6. The optimum reaction time was 5 min,15 min or 30 min for different cellulases extracted from different termites. And the optimum temperature for the three cellulases was between 35℃to 55℃. As for endo-P-1,4-glucanase, the highest enzyme activity(71.3±13.9 U/mg) was found in the crude extract obtained from R. chinensis, the next was found in that of Microcerotermes sp., M. barneyi, and Nasutitermes sp., respectively. The highest enzyme activity (33.0±1.7U/mg)ofβ-1,4-glucosidase was found in the crude extract obtained from M. barneyi, and the next was found in that of Microcerotermes sp., R. chinensis, and Nasutitermes sp., respectively. As for exo-β-1,4-glucanase, the highest enzyme activity (16.7±1.3U/mg)was found in the crude extract obtained from Microcerotermes sp., while the next was found in that of M. barneyi, Nasutitermes sp. and R. chinensis., respectively. The enzyme activities of three different cellulases retrived from different gut segments of R. chinensis, M. barneyi, Nasutitermes sp. and Microcerotermes sp. were different from one another, indicating that the acitivities of different cellulases may be closely related to the biological characteristics of termites and the distribution of the cellulases in the gut segments. Native-PAGE electrophoreses showed that there were different enzyme activity bands corresponding to endo-β-1,4-glucanases that distributed in different gut segments of the four termites, indicating that cellulose degradation in the termite gut is a complicated process that needs the involvement of many different cellulases.This study characterized the activity, diversity and distribution of three cellulases in the guts of four different termites that represent wood-feeding lower termites, fungus-cultivating termites and wood-feeding higher termites. The primary results obtained in this study form the bases for further studies on the mechanisms of the cellulose degradation in different termites, as well as the exploitation and utilization of termite cellulases in the new biomass energy industry.