Exploring Lignin Modification in the Gut of the Lower Termite Coptotermes Formosanus via Transcriptome Analysis

Termites have long been of academic interest due to their unique ability to digest lignocellulosic biomass and their efficiency at extracting sugars from cellulose is unmatched by any synthetic process. The collaborative breakdown of cellulose in the termite hindgut by the host and its consortium of bacterial, eukaryotic, and archaeal symbionts has been well studied and many useful cellulolytic enzymes have been discovered in that system. Less understood is how the termite processes the lignin component of its diet. Lignin, an irregular aromatic polymer, shields cellulose from being readily degraded and releases many toxic compounds when it is broken down. It represents a major bottleneck in industrial extraction of cellulosic sugars. Past work in the lower subterranean termite Coptotermes formosanus indicates that lignin is modified, but not greatly degraded as it passes through this organism’s digestive tract. In this work, we seek to elucidate the termite’s strategy for processing lignin using a differential transcriptome analysis of the foregut and midgut segments where lignin modification has been demonstrated. A transcriptomic differential expression analysis was employed to find genes responsive to the presence of lignin in the termite diet. Worker caste subterranean termites of the species Coptotermes formosanus were separately fed diets of pine wood (lignocellulose) and filter paper (cellulose). Transcriptomic foregut and midgut libraries of wood and paper fed termites were sequenced, assembled, and compared. Transcripts from a number of different functional categories were found to be more abundant in response to lignin, including several potentially lignin-modifying oxidoreductase class enzymes.