Vitamin B2 as a virulence factor in Pseudogymnoascus destructans skin infection

Abstract

Pathogenic and non-pathogenic related microorganisms differ in secondary metabolite production. Here we show that riboflavin overproduction by a fungal pathogen and its hyperaccumulation in affected host tissue exacerbates a skin infection to necrosis. In white-nose syndrome (WNS) skin lesions caused by Pseudogymnoascus destructans, maximum riboflavin concentrations reached up to 815 μg ml−1, indicating bioaccumulation and lack of excretion. We found that high riboflavin concentrations are cytotoxic under conditions specific for hibernation, affect bats’ primary fibroblasts and induce cell detachment, loss of mitochondrial membrane potential, polymerization of cortical actin, and cell necrosis. Our results explain molecular pathology of WNS, where a skin infection becomes fatal. Hyperaccumulation of vitamin B2 coupled with reduced metabolism and low tissue oxygen saturation during hibernation prevents removal of excess riboflavin in infected bats. Upon reperfusion, oxygen reacts with riboflavin resulting in dramatic pathology after arousal. While multiple molecules enable invasive infection, riboflavin-associated extensive necrosis likely contributes to pathophysiology and altered arousal pattern in infected bats. Bioaccumulation of a vitamin under natural infection represents a novel condition in a complex host-pathogen interplay.

Effect of torpor on host transcriptomic responses to a fungal pathogen in hibernating bats

“…The bats were removed from hibernation after 20 weeks, and long‐wavelength UV transillumination was used to identify putative P. destructans ‐infected and uninfected areas of the bat wing by the characteristic fluorescence of the fungus (Turner et al., ). The fluorescence is thought to be caused by metabolites produced by the fungus during invasion of bat tissue (Flieger et al., ; Mascuch et al., ). Four 5‐mm wing biopsies from each bat were collected and preserved in RNA‐Later: UV‐negative and UV‐positive tissues were sampled, although the bats were still torpid (4–6°C) and again, from the opposite wing, after the bats were allowed to warm to euthermic temperature for 60–90 min (Supporting Information Table ).…”

“…The bats were removed from hibernation after 20 weeks, and long-wavelength UV transillumination was used to identify putative P. destructans-infected and uninfected areas of the bat wing by the characteristic fluorescence of the fungus (Turner et al, 2014). The fluorescence is thought to be caused by metabolites produced by the fungus during invasion of bat tissue (Flieger et al, 2016;Mascuch et al, 2015).…”

White-nose syndrome increases torpid metabolic rate and evaporative water loss in hibernating bats

“…Recent reviews have summarized our understanding of disease mechanisms in WNS (17,45). A number of putative virulence factors have now been identified (14,29), and studies of both captive (42) and freeliving (33) bats indicate that the disease causes increased frequency of arousals from torpor during hibernation, emaciation, and death. Infected bats also exhibit signs of altered fluid, electrolyte, and pH balance (10,11,26,41,43), leading to development of two complementary mechanistic models of WNS pathophysiology (41,43).…”

AfricanSalmonellaTyphimurium sequence type 313 lineage 2 evades MAIT cell recognition by overexpressing RibB

“…Riboflavin promotes intracellular microbial survival and virulence during in vivo infection with Histoplasma capsulatum and Brucella abortus [60], [61]. In addition, accumulation of riboflavin is a candidate virulence factor in Pseudogymnoascus destructans skin infection [62].…”