Ultrastructural characterization of melanosomes of the human pathogenic fungus Fonsecaea pedrosoi

Melanin is a complex polymer widely distributed in nature and has been described as an important virulence factor in pathogenic fungi. In the majority of fungi, the mechanism of melanin formation remains unclear. In Fonsecaea pedrosoi, the major etiologic agent of chromoblastomycosis, melanin is sto...

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Published in:Journal of structural biology 2008-04, Vol.162 (1), p.75-84
Main Authors: Franzen, Anderson J., Cunha, Marcel M.L., Miranda, Kildare, Hentschel, Joachim, Plattner, Helmut, da Silva, Moises B., Salgado, Claudio G., de Souza, Wanderley, Rozental, Sonia
Format: Article
Language:English
Subjects:
Ascomycota - metabolism
Ascomycota - ultrastructure
Cell wall
Electron Probe Microanalysis
Fonsecaea pedrosoi
Humans
Immunohistochemistry
Melanin
Melanins - metabolism
Melanosome
Melanosomes - metabolism
Melanosomes - ultrastructure
Microscopy, Electron, Transmission
Mycoses - microbiology
X-ray microanalysis
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Summary:Melanin is a complex polymer widely distributed in nature and has been described as an important virulence factor in pathogenic fungi. In the majority of fungi, the mechanism of melanin formation remains unclear. In Fonsecaea pedrosoi, the major etiologic agent of chromoblastomycosis, melanin is stored in intracellular vesicles, named melanosomes. This paper details the ultrastructural aspects of melanin formation, its storage and transportation to the cell wall in the human pathogenic fungus F. pedrosoi. In this fungus, melanin synthesis within melanosomes also begins with a fibrillar matrix formation, displaying morphological and structural features similar to melanosomes from amphibian and mammalian cells. Silver precipitation based on Fontana-Masson technique for melanin detection and immunocytochemistry showed that melanosome fuses with fungal cell membrane where the melanin is released and reaches the cell wall. Melanin deposition in the fungal cell wall occurs in concentric layers. Antibodies raised against F. pedrosoi melanin revealed the sites of melanin production and storage in the melanosomes. In addition, a preliminary description of the elemental composition of this organelle by X-ray microanalysis and elemental mapping revealed the presence of calcium, phosphorus and iron concentrated in its matrix, suggesting a new functional role for these organelles as iron storage compartments.
ISSN:1047-8477
1095-8657
DOI:10.1016/j.jsb.2007.11.004