MSA - Systematics/Evolution
Urbina, Hector , Blackwell, Meredith .
Xylose fermenting genes: present in the Candida tanzawaensis clade associated with mushroom-feeding beetles.
Xylose, a major component of hemicellulose, is one of the most abundant renewable carbon sources on earth. Only a few yeast species scattered throughout the yeast (Saccharomycotina) phylogenetic tree are known to have the ability to ferment D-xylose to ethanol, potentially for biofuel production. The pathway is mediated by xylose reductase (XYL1), xylitol dehydrogenase (XYL2), and xylulose kinase (XYL3), enzymes that convert D-xylose to xylulose-5-phosphate. We characterized XYL1, XYL2, and XYL3 genes from two yeast classes: known xylose-fermenting strains and members of the Candida tanzawaensis clade isolated from the gut of mushroom-feeding beetles. Our results based on sequences of PCR products, indicated the presence of all three genes in the xylose-fermenting yeasts (C. jeffresii, C. tropicalis, Pichia guilliermondii, Sheffersomyces stipitis, and Spathaspora passalidarum). Interestingly, although XYL2 and XYL3 genes were present in most of the members of the C. tanzawaensis clade yeasts tested with 80% of sequence homology, we have not been able to amplify XYL1 from any of the members of this clade. These results are in concordance with the biochemical ability of C. tanzawaensis clade members to assimilate D-xylose and xylitol as sole carbon sources but not to ferment xylose. According to these results and in the absence of knowledge of the sister group of the C. tanzawaensis clade, we suggest that the ancestor for the C. tanzawaensis clade was capable of assimilating D-xylose. A change in the feeding behavior by an ancestral host insect from wood to basidiomata might have enabled the loss of XYL1 in the symbiotic yeasts.
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1 - Louisana State University, Biological Sciences , 202 Life Sciences Building, Baton Rouge, LA, 70803, United State
2 - Louisana State University, Biological Sciences Department, 202 Life Sciences Building, Baton Rouge, LA, 70803, United State
Presentation Type: Poster:Posters for Topics
Location: Event Tent/Cliff Lodge
Date: Tuesday, July 28th, 2009
Time: 5:30 PM