Vitamin B2 as a virulence factor in Pseudogymnoascus destructans skin infection.

Miroslav Flieger,Ondřej Šebesta,Jan Cerny,Veronika Kovacova,Jiri Pikula,Natália Martínková,Miroslav Kolarik,Petr Novák,Milada Chudíčková,Hana Bandouchova,Eva Stodůlková

doi:10.1038/srep33200

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.

Highlights

Pathogenic and non-pathogenic related microorganisms differ in secondary metabolite production
The extent of skin damage due to invasive growth of Pseudogymnoascus destructans (Fig. 1a) is visible under ultraviolet (UV) light transillumination, documenting lower disease intensity in a Palearctic bat compared to white-nose syndrome (WNS) lesions over extensive wing area in a Nearctic bat (Fig. 1b,c)
While fluorescent WNS spots contain 0.03–4.13 ng of P. destructans DNA per 7 mm[2] of wing biopsy based on quantitative polymerase chain reaction (Fig. 1a), flying membrane without UV fluorescence had significantly lower fungal loads

Summary

Introduction

Pathogenic and non-pathogenic related microorganisms differ in secondary metabolite production. Microorganisms produce metabolites to support their physiological functions and biotic interactions[1] These may induce deleterious toxicity and contribute to microbial pathogenicity or play crucial roles as compounds vital for animal metabolism. Among these metabolites, riboflavin (vitamin B2) enables microbial intracellular survival and promotes virulence[2,3,4]. We combine evidence from analytical chemistry, microbiology, pathology and cell biology to discover that accumulation of riboflavin within bat skin may act as a virulence factor of WNS This finding links existing data and hypotheses on WNS18–22 by revealing a novel mechanism of pathophysiology, operating in both torpid and euthermic animals

Methods

Results

Conclusion