Study On The Biochemical Mechanisms Of Lignocellulose Degradation By Odontotermes Formosanus (Isoptera: Termitidae)

Termites are important social insects. In natural environment, they play an obvious role in the turnover and mineralization of complex biopolymers such as lignocellulose by degrading dead trees and other cellulose-containing materials to more simple compounds. Termites are divided into lower termites and higher termites. The lower termites possess large numbers of symbiotic bacteria and flagellate protozoa that can assist lower termite by decomposing the cellulose in hind gut. The higher termites lack protozoa, and have a more elaborate external and internal anatomy and social organization than do the lower termites. The higher termites in the subfamily Macrotermitinae have established a special symbiotic relationship with fungus, so these termites are called fungus-growing termite. Because of the unique symbiotic relationship, many studies have been conducted on the relations between termites and fungus. The symbiotic fungi play a special role in the decomposition of plant litter ingested by higher termites. In order to better understand the role of the symbiotic fungi in the degradation of the cellulose and lignin and find organism with high activities of cellulase and ligninase, further studies on the activities of the fungus-growing termite and its symbiotic fungus are required.In this paper, we mainly determined the activities of cellulase in different castesof Odontotermes formosanus and the activities of cellulase and ligninase among theworker and soldier of the Odontotermes formosanus and its symbiotic fungiTermitomyces sp., at the same time, the amount of glucose between Odontotermesformosanus and its symbiotic fungi Termitomyces sp. was measured.Major research results are as follows: (1) Optimization of conditions for the determination of cellulase activity in Odontotermes formosanusThe Rotatable Orthogonal Central Composite Design and Response Surface Methodology were applied to optimize the conditions (pH value of buffer, substrate concentration, reaction temperature, and reaction time) for the determination of cellulase activity in Odontotermes formosanus. Empirical models were developed for describing the relationships between the reaction conditions and the cellulase activities. Statistical analysis indicated that the pH value of buffer, substrate concentration, reaction temperature, and reaction time had significant effects on the activities of the cellulase from O. formosanus. Under the condition that the pH value of buffer was 5.6, the substrate concentration was 1%, the reaction temperature was 55℃, and the reaction time was 15 min, the activity of endo-β-1,4-glucanase could reach 16.47 U/mg protein. Meanwhile, under the condition that the pH value of buffer was 5.6, the substrate concentration was 0.6%, the reaction temperature was 45℃, and the reaction time was 30 min, the activity ofβ-glucosidase could reach 17.86 U/mg protein.(2) Cellulase activities in different castes of O. formosanusThe activities of endo-β-1,4-glucanase andβ-glucosidase in worker, soldier, larvae and reproductives of O. formosanus were measured. The results indicated that there were significant differences in different castes (p<0.05). The workers expressed the highest activities of the endo-β-1,4-glucanase andβ-glucosidase. compared to the workers, the soldiers had lower activities of the endo-β-1,4-glucanase andβ-glucosidase, and the larvaes and the reproductives expressed the lowest activities of endo-β-1,4-glucanase andβ-glucosidase activities.(3) Activities of cellulase and ligninase in O. formosanus and its symbiotic fungus Termitomyces sp.The activities of the cellulase and ligninase in O. formosanus and its symbiotic fungus T. sp. were tested in this study. The results indicated that the worker termites, the soldier termites and the symbiotic fungus showed different activities of the cellulase and ligninase. The worker had the highest activities of the endo -β-1,4-glucanase andβ-glucosidase, compared to the worker, the soldier and the symbiotic fungus had the lower activities ofβ-glucosidase and endo -β-1,4-glucanase. As to the lignin peroxidase and manganase, the worker, the soldier and the symbiotic fungus had the low activities, however, the symbiotic fungus had the higher activities of laccase, of which the termites had little activities. The result can explain the "lignin degradation hypothesis" to some extent.(4) Determination of the amount of glucose between O. formosanus and its symbiotic fungus T. sp.The amount of glucose between O. formosanus and its symbiotic fungus T. sp. were measured, at the same time, we mixed the enzyme extracts of symbiotic fungus T. sp. into different castes of O. formosanus with the ratio 1:2, 1:4. 1:6 and 1:8 (protein conternt ratio), respectively, The amount of glucose of the mixture was measured, too. The results indicated that the glucose existed in the enzyme extracts of all castes of O. formosanus and its symbiotic fungus T. sp. The mixture of enzyme extracts between the worker and the symbiotic fungus showed higher glucose content, the amount of glucose of which was significant higher than that of enzyme extracts of the worker and enzyme extracts of the symbiotic fungus (p<0.05). This phenomenon was also existed in the mixture of enzyme extracts between the soldier and the symbiotic fungus, but not existed in the mixture of enzyme extracts between the larvae and the symbiotic fungus, the mixture of enzyme extracts between the worker and the soldier and the mixture of enzyme extracts between the larvae and the worker. This phenomenon can provide new proofs for explaining the relationship between higher termite and symbiotic fungus.