Abstract
The two black yeasts Exophiala dermatitidis and Exophiala spinifera that are clinically considered as the most virulent species potentially causing disseminated infections are both producing extracellular capsule-like material, are compared. In this study, 10 genomes of E. spinifera and E. dermatitidis strains, including both clinical and environmental isolates, were selected based on phylogenetic analysis, physiology tests and virulence tests, sequenced on the Illumina MiSeq sequencer and annotated. Comparison of genome data were performed between intraspecific and interspecific strains. We found capsule-associated genes were however not consistently present in both species by the comparative genomics. The prevalent clinical species, E. dermatitidis, has small genomes containing significantly less virulence-associated genes than E. spinifera, and also than saprobic relatives. Gene OG0012246 and Myb-like DNA-binding domain and SANT/Myb domain, restricted to two strains from human brain, was shared with the neurotropic species Rhinocladiella mackenziei. This study indicated that different virulence profiles existed in the two capsule-producing black yeasts, and the absence of consistent virulence-associated profiles supports the hypothesis that black yeasts are opportunists rather than primary pathogens. The results also provide the key virulence genes and drive the continuing research forward pathogen–host interactions to explore the pathogenesis.
Highlights
Black yeasts in the ascomycete order Chaetothyriales are relatively frequent opportunistic agents of human disease
I.e., the number of published cases and their severity (Sudhadham et al, 2008; de Hoog et al, 2019) it has been concluded that E. dermatitidis and E. spinifera are the most
Exophiala dermatitidis is a common environmental species occurring in the domesticated environment (Isola et al, 2013; Gümral et al, 2014) and has a higher chance to of infection; it has a significantly lower number (n = 267–403) of virulenceassociated genes than all species compared, including the common environmental species E. oligosperma (n = 424)
Summary
Black yeasts in the ascomycete order Chaetothyriales are relatively frequent opportunistic agents of human disease. The black yeasts and relatives mitigate external stress of, e.g., dryness and irradiation by melanin, and detrimental effects of toxin can be compensated by pathways of the cytochrome P450 (Moreno et al, 2018) aiding degradation and co-assimilation of monoaromatic hydrocarbons This combination of vitality factors provides a wide array of survival strategies, and it may be hypothesized that species with the most pronounced development of such pathways may have a higher ability of tissue invasion. Both species are able to disseminate in susceptible patients with formation of cutaneous acanthosis, but a difference in clinical predilection has been noted: E. dermatitidis has a tendency of neurotropism, whereas E. spinifera seems to be somewhat osteotropic (Song et al, 2017) This suggests that opportunism in these fungi might be fine-tuned
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