HapX Mediates Iron Homeostasis in the Pathogenic Dermatophyte Arthroderma benhamiae but Is Dispensable for Virulence.

Antje Kröber,Ekaterina Shelest,Peter Hortschansky,Axel A Brakhage,Kirstin Scherlach,Peter Staib,Olaf Kniemeyer,Gustavo Henrique Goldman

doi:10.1371/journal.pone.0150701

Antje Kröber, Ekaterina Shelest + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0150701

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Abstract

For many pathogenic fungi, siderophore-mediated iron acquisition is essential for virulence. The process of siderophore production and further mechanisms to adapt to iron limitation are strictly controlled in fungi to maintain iron homeostasis. Here we demonstrate that the human pathogenic dermatophyte Arthroderma benhamiae produces the hydroxamate siderophores ferricrocin and ferrichrome C. Additionally, we show that the iron regulator HapX is crucial for the adaptation to iron starvation and iron excess, but is dispensable for virulence of A. benhamiae. Deletion of hapX caused downregulation of siderophore biosynthesis genes leading to a decreased production of siderophores during iron starvation. Furthermore, HapX was required for transcriptional repression of genes involved in iron-dependent pathways during iron-depleted conditions. Additionally, the ΔhapX mutant of A. benhamiae was sensitive to high-iron concentrations indicating that HapX also contributes to iron detoxification. In contrast to other pathogenic fungi, HapX of A. benhamiae was redundant for virulence and a ΔhapX mutant was still able to infect keratinized host tissues in vitro. Our findings underline the highly conserved role of the transcription factor HapX for maintaining iron homeostasis in ascomycetous fungi but, unlike in many other human and plant pathogenic fungi, HapX of A. benhamiae is not a virulence determinant.

Highlights

The fungal pathogen Arthroderma benhamiae belongs to a group of fungi known as dermatophytes, which exclusively infect keratinized structures such as hair, skin and nails of humans and animals [1]
HapX of A. benhamiae displays all the typical characteristics which are common to this class of transcription factors, including the basic region leucine zipper and coiled-coil domains mediating DNA-binding, an N-terminal CCAAT-binding complex (CBC) domain, which is essential for interaction with the CCAATbinding complex (CBC) subunit HapE [18] and four conserved cysteine-rich regions (CRR) (S1 Fig)
In A. fumigatus, two of the four CRR are known to be involved in detoxification of iron excess [22]

Summary

Methods

2 were grown on SAB supplemented with 200 μg/ml hygromycin (ForMedium, Hunstanton, UK) or G418 (Carl Roth, Karlsruhe, Germany), according to the selectable marker used. Production of microconidia was performed on MAT agar [0.1% (w/v) peptone, 0.2% (w/v) glucose, 0.1% (w/v) MgSO4, 0.1% (w/v) KH2PO4; Carl Roth, Karlsruhe, Germany] if not otherwise stated. For harsh iron starvation conditions, the ferrous iron chelator bathophenanthroline disulfonic acid Na2-salt (BPS) (Serva, Heidelberg, Germany) was used at a final concentration of 0.2 mM (-Fe +BPS). The ferric iron chelator deferoxamine mesylate salt (DFOM) (Sigma-Aldrich, Taufkirchen, Germany) was added to the medium at a final concentration of 10 μM (-Fe +DFOM). 104 microconidia of A. benhamiae wild type, ΔhapX mutant and hapXC reconstituted strain were spotted on solid AMM agar supplemented with iron concentrations ranging from 1–10 mM FeSO4

Results

Discussion

Conclusion