Environmental prospecting of black yeast-like agents of human disease using culture-independent methodology

Abstract

Melanized fungi and black yeasts in the family Herpotrichiellaceae (order Chaetothyriales) are important agents of human and animal infectious diseases such as chromoblastomycosis and phaeohyphomycosis. The oligotrophic nature of these fungi enables them to survive in adverse environments where common saprobes are absent. Due to their slow growth, they lose competition with common saprobes, and therefore isolation studies yielded low frequencies of clinically relevant species in environmental habitats from which humans are thought to be infected. This problem can be solved with metagenomic techniques which allow recognition of microorganisms independent from culture. The present study aimed to identify species of the family Herpotrichiellaceae that are known to occur in Brazil by the use of molecular markers to screen public environmental metagenomic datasets from Brazil available in the Sequence Read Archive (SRA). Species characterization was performed with the BLAST comparison of previously described barcodes and padlock probe sequences. A total of 18,329 sequences was collected comprising the genera Cladophialophora, Exophiala, Fonsecaea, Rhinocladiella and Veronaea, with a focus on species related to the chromoblastomycosis. The data obtained in this study demonstrated presence of these opportunists in the investigated datasets. The used techniques contribute to our understanding of environmental occurrence and epidemiology of black fungi.

Figure 1

Herpotrichiellaceous sequences encountered in investigated datasets. (A) Geographic metagenomic data distribution. (B) Total of reads in investigated datasets. (C) Herpotrichellaceous sequences per dataset. The image was created using Adobe Photoshop CC (v. 20.0.4) based on the map (https://commons.wikimedia.org/wiki/File:20111110231441!Estados_de_nascimento_de_presidentes_brasileiros.png), which is available under a Creative Commons license https://creativecommons.org/licenses/by-sa/3.0/deed.en.

Figure 2

Fluxogram of identification in silico. In green criteria of selection and in red rejected criteria.