Digestome of the termite, coptotermes curvignathus holmgren as a source of novel lignocellulases

Researchers have made extensive efforts to determine the lignocellulose degrading potential genes in herbivorous insect, which might assist in reducing the cost of biofuel production via treatment of lignocelluloses. This project was carried out using Coptotermes curvignathus, a subterranean termite that has an important impact economically on both agricultural lands and plantations by causing deaths of crop plants, whether in sapling or mature form. Hence, the ability of C. curvignathus to feed on living trees and overcome the barriers and defenses of plants is intriguing. The objectives of this study are to discover the Carbohydrate-Active enzymes (CAZyme) related genes in C. curvignathus, illustrate a potential pathway for lignocelluloses degradation in the digestive system, and discover the genes involved in the defensive system. To achieve these objectives, a transcriptomic gene library was constructed using digestive tracts from 200 insects, from which mRNA was isolated to generate a cDNA library. The cDNA library was sequenced in Next Generation Sequencing via Illumina HiSeq 2000. Raw data were trimmed and assembled by SolexaQA and Bowtie before loading into Gene Ontology based data mining software, Blast2GO (B2G). Assembled transcriptome were loaded into CAZyme analysis toolkits to identify CAZyme genes present in the data. Data were also analysed based on insect innate immunity database (IIID). The result from the study showed the presence of expressed gene encoding lignocellulose of CAZyme residing in C. curvignathus that fed in different habitat, with about 68% of the common CAZyme families encoded transcripts from mineral habitat which were expressed to be higher than peat habitat. As compared to Reticuliformis flavipes and Coptotermes formosanus, ten CAZyme families (GH16, GH22, GH23, GH32, GH73, GT90, CE15, CBM3, CBM5 and CBM50) were found only in C. curvignathus. In addition, in this study, expression profile for Auxiliary Activity (AA) of a new family of CAZyme is presented to show that lignin degradation is significant in C. curvignathus lignocellulosic digestion. The lignocellulose degrading pathway was illustrated in this study to show the complex mechanism on how C. curvignathus digest lignocellulose material. Lastly, this study has discovered several important expressed genes, such as GH22 and GH23 that are related to host immune system and detoxification. In conclusion, this project is hoped to adapt the usage of C. curvignathus CAZyme ability in industrial lignocellulose degradation and also improve the agricultural sector in the control of C. curvignathus through the finding of defence related transcriptome such as GH22 and GH23. It is also recommended to study each of the ten unique gene found in this study in detail via protein expression, which will determine the actual function in C. curvignathus.

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