부산대학교 도서관

Chelura terebrans is a widely distributed wood boring amphipod belonging to the little studied family Cheluridae. Previous studies have hinted that C. terebrans belongs to a small number of animals capable of degrading lignocellulose without the aid of symbiotic gut microorganisms. This study utilises a broad range of techniques to gain a better understanding of C. terebrans and their ability to digest wood. Molecular phylogenetic analyses of two Chelurid species largely agree with the current taxonomic organisation of this family. Examination of C. terebrans using scanning electron microscopy has offered a better understanding of their digestive system and revealed, with the exception of robust lateralia, few morphological adaptations to accommodate such an unusual diet. This examination also found no evidence of gut-resident microflora. Furthermore, quantitative real-time PCR confirmed the absence of any substantial resident symbiotic extra- or intracellular bacteria in the digestive tract by revealing very low levels of bacterial 16S gene sequences in comparison to the symbiont-containing isopod Porcellio scaber. Despite finding no evidence for resident symbiont gut-microflora, in-gel and in vitro enzymatic assays using extracts isolated from the hepatopancreas suggests that C. terebrans possesses a considerable repertoire of endogenous enzymatic capabilities useful for the digestion of wood, including mannosidase, β-glucosidase and β-xylosidase, endo-1, 4-β-glucanase and endo-1, 4-β-xylanase, with extracts also possessing mono- and diphenol oxidase activity. Furthermore, mass spectrometry analysis on gel regions presenting high mono- and diphenol oxidase activity detected several proteins belonging to the glycosyl hydrolase family and haemocyanins. Two transcriptomic libraries were obtained from the hepatopancreases of C. terebrans fed on a diet of either beech (Fagus sylvatica) or Scots pine (Pinus sylvestris). These data provided sequences and the relative abundances of genes thought to be involved in lignocellulose digestion. In both cases, a significant number of the total ESTs contributed towards contigs corresponding to genes for glycosyl hydrolases and haemocyanins. Furthermore, overall expression of each glycosyl hydrolase suggested variation according to the substrate on which C. terebrans were fed. Comparisons of the relative gene expression seen in the C. terebrans transcriptome with those found in both the wood boring isopod Limnoria quadripunctata and the non boring amphipod Echinogammarus marinus offer insight into the genes important for lignocellulose digestion. This study represents substantial progress in our understanding of how C. terebrans digests wood and has also opened up new avenues of investigation by revealing C. terebrans as a potential source of novel lignocellulolytic enzymes.