Abstract
Members of the fungal genus Fonsecaea causing human chromoblastomycosis show substantial geographic structuring. Genetic identity of clinical and environmental strains suggests transmission from plant debris, while the evolutionary processes that have led to spatially separated populations have remained unexplained. Sequences of ITS, BT2, ACT1, Cdc42, Lac and HmgA were analyzed, either by direct sequencing or by cloning. Thirty-seven clinical and environmental Fonsecaea strains from Central and South America, Asia, Africa and Europe were sequenced and possible recombination events were calculated. Phylogenetic trees of Cdc42, Lac and HmgA were statistically supported, but ITS, BT2 and ACT1 trees were not. The Standardized Index of Association (IA S) did not detect recombination (IA S = 0.4778), neither did the Phi-test for separate genes. In Fonsecaea nubica non-synonymous mutations causing functional changes were observed in Lac gene, even though no selection pressures were detected with the neutrality test (Tajima D test, p>0.05). Genetic differentiation of populations for each gene showed separation of American, African and Asian populations. Strains of clinical vs. environmental origin showed genetic distances that were comparable or lower than found in geographic differentiation. In conclusion, here we demonstrated clonality of sibling species using multilocus data, geographic structuring of populations, and a low functional and structural selective constraint during evolution of the genus Fonsecaea.
Highlights
The genus Fonsecaea comprises etiologic agents of human chromoblastomycosis, a chroniccutaneous infection eventually leading to cauliflower-like eruptions on the skin [1,2]
Fungal Strains and Culture Conditions Seventeen strains of F. pedrosoi, 12 of F. monophora, 8 of F. nubica (Table 1) and one of a neighbouring Cladophialophora species were obtained from the reference collection of the Centraalbureau voor Schimmelcultures Fungal Biodiversity Centre (Utrecht, the Netherlands), in addition to fresh strains recovered from patients, and environmental isolates
In the evolution of black fungi [30], we witness a functional change from a rock-inhabiting life style prevalent in ancestral Coniosporium (Knufia) and relatives to an increased ability to infect humans and other vertebrates in derived clades
Summary
The genus Fonsecaea comprises etiologic agents of human chromoblastomycosis, a chronic (sub)cutaneous infection eventually leading to cauliflower-like eruptions on the skin [1,2]. Far the etiologic agents within Fonsecaea are limited to three closely related siblings composing a clearly delimited clade [10]: Fonsecaea pedrosoi, F. monophora and F. nubica. Environmental sampling to recover the species from their supposed natural habitat has been done [8,9]. The majority of Fonsecaea-like strains concerned non-virulent species, which were not frequently isolated from on human infections [8]. Either the natural habitat of pathogenic Fonsecaea species has to be found somewhere else, or, alternatively, the species have some kind of advantage of being carried by a mammal host. The existence of evolutionary processes supporting the latter hypothesis may be revealed by comparing patterns of variability and distribution of potential etiologic agents
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