Master of Science (MS)


Biological Sciences

Document Type



Scheffersomyces stipitis (=Pichia stipitis) is a xylose-fermenting and assimilating yeast (Ascomycota: Saccharomycotina) consistently isolated from the gut of Odontotaenius disjunctus (Coleoptera: Passalidae). This filamentous yeast is often attached to the wall of the posterior hindgut of the beetle by a holdfast. Gallery walls of white-rotted wood inhabited by the beetle are lined with macerated wood and frass that includes the yeast and other microbes. Previous studies have mentioned the relationship between the passalid and this yeast; however, passalid beetles also harbor a community of prokaryotes in their guts that have not been characterized. Experiments using culturing and cloning techniques and whole gut isolations have been performed in this work to characterize gut microbes. Introduction of yeast-free diets as well as diets lacking hemicellulose backbone components xylose and xylan served to test the hypothesis that S. stipitis is associated with the beetle host due to continuous environmental transmission. Treatments with antibiotics were attempted to selectively remove the yeast that is attached to the gut. Because attempts to cure the beetle of the yeast failed, introduction of foreign yeasts was performed to determine if the hindgut is saturated with microbes and to determine if the native yeast can be removed or replaced. Microsatellite and species-specific probes were used to confirm that the identity of the yeasts recovered were the same as those introduced. Results showed six taxa of three major groups, γ-Proteobacteria, β-Proteobacteria, and Firmicutes, were represented in easily isolated, culturable prokaryotes of passalid beetle guts. Diet manipulation without removing the native yeast suggested that continued recruitment from the environment might not be necessary for adults for up to 11 days. All treatments with antibiotics failed to selectively remove the yeast from the beetle surface and gut. Yeasts introduced in feeding experiments showed that non-native yeasts could be maintained for up to ten days after feeding, evidenced by microsatellite primers; however, the native yeast was never displaced. Production of a holdfast by the non-native yeasts was not observed when gut tissues were examined with light microscopy. Additionally, killer factors of the native and foreign yeasts were not discovered.



Document Availability at the Time of Submission

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Committee Chair

Blackwell, Meredith