Transcriptome Study of an Exophiala dermatitidis PKS1 Mutant on an ex Vivo Skin Model: Is Melanin Important for Infection?

Abstract

The black yeast Exophiala dermatitidis is a polyextremophilic human pathogen, especially known for growing in man-made extreme environments. Reported diseases caused by this fungus range from benign cutaneous to systemic infections with 40% fatality rate. While the number of cases steadily increases in both immunocompromised and immunocompetent people, detailed knowledge about infection mechanisms, virulence factors and host response are scarce. To understand the impact of the putative virulence factor melanin on the infection, we generated a polyketide synthase (PKS1) mutant using CRISPR/Cas9 resulting in a melanin deficient strain. The mutant and the wild-type fungus were inoculated onto skin explants using an ex vivo skin organ culture model to simulate in vivo cutaneous infection. The difference between the mutant and wild-type transcriptional landscapes, as assessed by whole RNA-sequencing, were small and were observed in pathways related to the copper homeostasis, cell wall genes and proteases. Seven days after inoculation the wild-type fungus completely colonized the stratum corneum, invaded the skin and infected keratinocytes while the mutant had only partially covered the skin and showed no invasiveness. Our results suggest that melanin dramatically improves the invasiveness and virulence of E. dermatitidis during the first days of the skin infection.

The transcriptomic and phenotypic response of the melanized yeast Exophiala dermatitidis to ionizing particle exposure

“…Alternatively, however, there are still physiological aspects of melanization that need to be studied: we saw a massive transcriptomic response to melanization in C. neoformans [28], and here nearly 1000 unique proteins were differentially expressed only in melanized cells in response to particle exposure. These genes represent candidates to concentrate on to determine how melanin interacts with IR, but the observation that they are not enriched for any particular biological function underscores the complex effects melanin has in fungi [62], the understanding of which can most successfully be addressed through genetic analyses.…”

Proteomics Reveals Distinct Changes Associated with Increased Gamma Radiation Resistance in the Black Yeast Exophiala dermatitidis

“…However, equally important are other features that make E. dermatitidis amenable for experimentation, including: A modest genome size among dermatophytes; a relatively quick growth rate (reaching stationary phase in < 48 h); a relatively high transformation and homologous recombination rate, which has allowed for functional characterization of dozens of its genes. Other major areas of investigation with E. dermatitidis have been its resistance to γ-radiation-induced damage [ 9 , 18 , 19 , 20 , 21 ] and its melanin biosynthetic pathway, which is constitutively active in E. dermatitidis and has been scrutinized at the phenotypic (e.g., virulence) and genetic level for more than twenty years [ 22 , 23 ].…”

Genomics and Virulence of Fonsecaea pugnacius, Agent of Disseminated Chromoblastomycosis

“…The MEROPS S (serine) and M (metallo) peptidase families were the highest in number in the analyzed species causing brain infection. These two groups have been reported to be significantly enriched in transcriptome analyses of E. dermatitidis during infection (Poyntner et al, 2018). Among the Serine families, classes S33 and S9 were more numerous (Supplementary Table 3), both involved in prolyl metabolism.…”