Molecular insight into lignocellulose digestion by a marine isopod in the absence of gut microbes.
The digestion of lignocellulose is attracting attention both in terms of basic research into its metabolism by microorganisms and animals, and also as a means of converting plant biomass into biofuels. Limnoriid wood borers are unusual because, unlike other wood-feeding animals, they do not rely on symbiotic microbes to help digest lignocellulose. The absence of microbes in the digestive tract suggests that limnoriid wood borers produce all the enzymes necessary for lignocellulose digestion themselves. In this study we report that analysis of ESTs from the digestive system of Limnoria quadripunctata reveals a transcriptome dominated by glycosyl hydrolase genes. Indeed, > 20% of all ESTs represent genes encoding putative cellulases, including glycosyl hydrolase family 7 (GH7) cellobiohydrolases. These have not previously been reported in animal genomes, but are key digestive enzymes produced by wood-degrading fungi and symbiotic protists in termite guts. We propose that limnoriid GH7 genes are important for the efficient digestion of lignocellulose in the absence of gut microbes. Hemocyanin transcripts were highly abundant in the hepatopancreas transcriptome. Based on recent studies indicating that these proteins may function as phenoloxidases in isopods, we discuss a possible role for hemocyanins in lignin decomposition.
King
Andrew J
AJ
Centre for Novel Agricultural Products, Department of Biology, University of York, PO Box 374, York YO10 5YW, UK.
Cragg
Simon M
SM
Li
Yi
Y
Dymond
Jo
J
Guille
Matthew J
MJ
Bowles
Dianna J
DJ
Bruce
Neil C
NC
Graham
Ian A
IA
McQueen-Mason
Simon J
SJ
D000818:Animals; D018533:Biomass; D004156:Catechol Oxidase / Q000235:genetics / Q000378:metabolism; D044602:Cellulases / Q000235:genetics / Q000378:metabolism; D017753:Ecosystem; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism; D020224:Expressed Sequence Tags; D041981:Gastrointestinal Tract / Q000378:metabolism / Q000382:microbiology; D020869:Gene Expression Profiling; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism; D006433:Hemocyanins / Q000235:genetics / Q000378:metabolism; D043143:Hepatopancreas / Q000378:metabolism; D033321:Isopoda / Q000033:anatomy & histology / Q000235:genetics* / Q000378:metabolism* / Q000382:microbiology; D008031:Lignin / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D010802:Phylogeny; D014934:Wood
D004792:Enzyme Precursors; C036909:lignocellulose; D008031:Lignin; D006433:Hemocyanins; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D044602:Cellulases; D006026:Glycoside Hydrolases