Pseudogymnoascus destructans and White Nose Syndrome

Background: 

Pseudogymnoascus destructans (Pds) is the causative agent of White Nose Syndrome (WNS) in North American bat species, which has been wreaking havoc on bat populations throughout the United States and Canada.

First documented in Albany, NY in 2006, WNS has now been confirmed in 23 states and 7 Canadian provinces.  The namesake of this disease is the white, fuzzy fungal growth on the muzzle of infected bats, however, the infection spans the entire body of the bat, most notably on the wings, where degradation is very prominent and destructive, leading to dehydration, fat depletion and more frequent arousals from hibernation.

Click here for more background information on White Nose Syndrome and Pseudogymnoascus destructans 

Research: Pseudogymnoascus destructans and the Alternative Host Hypothesis

Fungi that infect mammals are notoriously opportunistic. The Alternative Host Hypothesis (Casadevall et al. 2003) classifies these fungal opportunists as environmental pathogenic fungi (EPF) due to their ability to persist in both the environment and on host species. Cryptococcus neoformans, a basidiomycete yeast, is used as a model to explain the Alternative Host Hypothesis. In this model, Casadevall et al. (2003) identifies “dual use virulence genes”. As their name suggests, these genes serve a dual function for the fungus. Primarily, these genes allow for survival of the fungus in the environment, however, these same genes also happen to have a major impact on its ability to infect a host organism. The pathogenic capabilities provided by these  genes may be attributed to common environmental pressures placed on the fungus, such as, in the case of C. neoformans, predatory amoebas, nematodes and slime molds in the soil.

We hypothesized that P. destructans would fit the model of an Environmental Pathogenic Fungus (EPF), showing the ability to grow saprophytically in an environment it shares with its bat host (i.e. cave walls, soil, cave plants). Both C. neoformans and species in the genus Pseudogymnoascus have been co-isolated from moss in polar regions (Arenz et al. 2006). Growing the moss Polytrichum commune in vitro, I was able to show the ability of P. destructans to successfully colonize and reproduce on the living moss tissue in vitro. Our results supported the hypothesis that P. destructans does not need a bat host to survive and reproduce, and that it could fall under the definition of an EPF.

My next task was to attempt to identify potential virulence genes in P. destructans by using BLAST to compare amino acid sequences of the already identified C. neoformans dual use virulence genes with the genome of P. destructans, which is openly available on the Broad Institute database. Three dual use virulence genes had very high matches with the P. destructans genome: urease, superoxide dismutase, and aspartyl protease. To my knowledge, this is the first publication elucidating potential virulence genes in this organism.

I conducted this research while attending Lock Haven University for my BS in Biology, in the lab of Dr. Barrie Overton. A nice write up on his lab and research can be found in the My Haven Alumni magazine published for the Spring of 2014, as well as in this newsletter from the gantdaily.com

Literature Cited: 

Arenz, B.E., B.W. Held, J.A. Jurgens, R.L. Farrell, and R.A. Blanchette. 2006. Fungal diversity in soils and historic wood from the Ross Sea Region of Antarctica. Soil Biology & Biochemistry, 38:3057–3064.

Casadevall, A., J.N. Steenbergen, and J.D. Nosanchuk. 2003. ‘Ready-made’ virulence and ‘dual use’ virulence factors in pathogenic environmental fungi—the Cryptococcus neoformans paradigm. Current Opinion in Microbiology, 6: 332–337.

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