Growth medium and incubation temperature alter the Pseudogymnoascus destructans transcriptome: implications in identifying virulence factors

Abstract

Pseudogymnoascus destructans is the causal agent of bat white-nose syndrome (WNS), which is devastating some North American bat populations. Previous transcriptome studies provided insight regarding the molecular mechanisms involved in WNS; however, it is unclear how different environmental parameters could influence pathogenicity. This information could be useful in developing management strategies to mitigate the negative impacts of P. destructans on bats. We cultured three P. destructans isolates from Atlantic Canada on two growth media (potato dextrose agar and Sabouraud dextrose agar) that differ in their nitrogen source, and at two separate incubation temperatures (4 C and 15 C) that approximate the temperature range of bat hibernacula during the winter and a temperature within its optimal mycelial growth range. We conducted RNA sequencing to determine transcript levels in each sample and performed differential gene expression (DGE) analyses to test the influence of growth medium and incubation temperature on gene expression. We also compared our in vitro results with previous RNA-sequencing data sets generated from P. destructans growing on the wings of a susceptible host, Myotis lucifugus. Our findings point to a critical role for substrate and incubation temperature in influencing the P. destructans transcriptome. DGE analyses suggested that growth medium plays a larger role than temperature in determining P. destructans gene expression and that although the psychrophilic fungus responds to different nitrogen sources, it may have evolved for continued growth at a broad range of low temperatures. Further, our data suggest that down-regulation of the RNA-interference pathway and increased fatty acid metabolism are involved in the P. destructans-bat interaction. Finally, we speculate that to reduce the activation of host defense responses, P. destructans minimizes changes in the expression of genes encoding secreted proteins during bat colonization.

Transcriptional host–pathogen responses of Pseudogymnoascus destructans and three species of bats with white-nose syndrome

“…Four of the transcripts produced by P. destructans in lesions are similar to aspartic proteases secreted by Aspergillus that degrade keratin [65], but these were not consistently up-regulated among species (Table 1). Instead, we observed similar responses by the fungus to growth in saprophytic and pathogenic conditions on M. myotis and M. lucifugus, supporting the "accidental pathogen" hypothesis [32,37].…”

“…However, potential targeted responses of P. destructans to saprophytic and pathogenic growth on bat wings have not yet been characterized. Two competing hypotheses exist: (1) that P. destructans is an "accidental pathogen" whose saprophytic growth also facilitates invasion of bat tissue, and (2) that P. destructans exhibits specific pathogenic responses in the wing tissue of bats, which differ from its saprophytic growth in vitro, on cave substrates, or on the surface of bat wings [37].…”

Comparative eco-physiology revealed extensive enzymatic curtailment, lipases production and strong conidial resilience of the bat pathogenic fungus Pseudogymnoascus destructans

“…They also influence fungal growth, adherence and dissemination inside the host 46 . Our comparative eco-physiological approach proposes outstanding role of lipid and fatty acid degradation in the virulence of P. destructans, as already noted by Donaldson et al 29 based on transcriptomic data. Given the facts that P. destructans lacks keratinolytic activity and that phospholipids are a major component of all cell membranes, lipases are probably the most important enzymes allowing fungal hyphae to digest and invade the integumentary structures of infected skin, forming cup-like erosions diagnostic of the white-nose syndrome.…”

Two subspecies of bent-winged bats (Miniopterus orianae bassanii and oceanensis) in southern Australia have diverse fungal skin flora but not Pseudogymnoascus destructans

“…While Sabouraud’s broth has been shown to be an effective growth medium for the culture of P . destructans [ 53 ] dextrose-peptone-yeast extract agar produces more viable colonies [ 54 ]. However, as this study was not concerned with growing viable colonies of P .…”