The gut of insects and plant tissues are productive sources for the isolation of undescribed species of yeasts. In particular, the gut of lignicolous insects is colonized by yeasts that can carry out the fermentation of several sugars. The consistent association between xylose-fermenting (X-F) yeasts and the gut of lignicolous insects has been used as evidence of a symbiotic relationship between them. In general passalid beetles (Passalidae) and wood-roaches (Cryptocercidae) feed on rotted wood where they spend most of their lives. Digestion of the substrate depends on the symbiotic microbiota, which include strict and facultative anaerobic microorganisms such as bacteria, parabasalids, and fungi. The objectives of this study were to describe the yeasts associated with hardwoods in Louisiana (Chapter 2), the gut of the wood roach Cryptocercus collected in the Appalachian Mountains (Chapter 3), passalids collected in Guatemala (Chapter 4) and in Thailand (Chapter 5), and to study selection acting on xylose reductase (XR) in yeasts (Chapter 6). This study confirmed the routine presence of ascomycete yeasts from the clades Scheffersomyces, Spathaspora, Lodderomyces, and Sugiyamaella in the guts of wood roaches and passalid beetles, as well as basidiomycete yeasts in the genera Cryptococcus and Trichosporon in passalids exclusively. In this investigation, four new X-F yeasts, Scheffersomyces illinoinensis, Sc. quercinus, Sc. virginianus, and Sc. cryptocercus, were proposed based on multilocus phylogenetic analyses, molecular, and biochemical characterization. The X-F yeasts in the Scheffersomyces clade were the most abundant species in the gut of both wood-roaches and Guatemalan passalids, results that support and expand the previously described relationship between X-F yeasts and lignicolous insects. This finding, however, was not observed in Thai passalids, where the most abundant yeasts were closely related to Candida insectamans (Spathaspora clade) that does not ferment xylose. In addition, this study determined that the gut of lignicolous insects is a niche rich in undescribed yeasts classified in several clades. The xylose reductase gene (XYL1) has been shown to be useful as a molecular marker for rapid identification of cryptic yeast species, and the xylose reductase enzyme (XR) has been exposed to purifying selection in ascomycete yeasts.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-11082012-161610 |
| Date | 14 November 2012 |
| Creators | Urbina, Hector Raul |
| Contributors | Cronin, James, Thune, Robert, Aime, Cathie, Sheldon, Frederick, Blackwell, Meredith |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-11082012-161610/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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