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Morphometric and densitometric study of the biogenesis of electron-dense granules in Fonsecaea pedrosoi
A J Franzen1, W de Souza, M Farina
1Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21949-900, Brazil.
Abstract:
Fonsecaea pedrosoi is a polymorphic pathogenic fungus, etiological agent of chromoblastomycosis, that synthesizes a melanin-like pigment. Although this pigment has been described as a component of the outer layers of the cell wall, electron-dense cytoplasmic bodies have also been visualized. In this work, we have correlated the appearance of intracellular electron-dense granules with the melanization process in F. pedrosoi. For this, conidial forms were grown under conditions where melanin was not synthesized. Afterwards, cells were incubated in Hank's medium supplemented with bovine fetal serum, at 37 degrees C, to stimulate the pigment production. The genesis of cytoplasmic bodies, with different stages of electron density, was demonstrated by transmission electron microscopy. The appearance of fungal acidic compartments, visualized by confocal laser scanning microscopy in cells stained with acridine orange, was time coincident with the formation of electron-dense granules observed by transmission electron microscopy. The quantification of granule numbers as well as morphometric and densitometric studies were performed.
Insights
Fonsecaea pedrosoi, a fungus causing chromoblastomycosis, produces melanin. This study reveals intracellular granules forming during melanization, linked to acidic compartments within the fungal cells.
Area of Science:
- Medical Mycology
- Cell Biology
- Biochemistry
Background:
- Fonsecaea pedrosoi is a pathogenic fungus responsible for chromoblastomycosis.
- This fungus synthesizes a melanin-like pigment, traditionally associated with its cell wall.
- Intracellular electron-dense bodies have been observed, but their role in melanization is unclear.
Purpose of the Study:
- To correlate the formation of intracellular electron-dense granules with the melanization process in Fonsecaea pedrosoi.
- To investigate the origin and characteristics of these cytoplasmic bodies.
- To understand the relationship between fungal acidic compartments and pigment synthesis.
Main Methods:
- Culturing Fonsecaea pedrosoi conidial forms under non-melanizing and melanizing conditions.
- Transmission electron microscopy (TEM) to visualize intracellular granules.
- Confocal laser scanning microscopy (CLSM) with acridine orange staining to identify acidic compartments.
- Quantitative analysis including granule counting, morphometry, and densitometry.
Main Results:
- Intracellular electron-dense granules were observed to form during the melanization process.
- The genesis of these granules, showing varying electron densities, was visualized using TEM.
- The appearance of fungal acidic compartments, detected by CLSM, coincided temporally with granule formation.
- Quantitative and morphometric analyses supported the correlation between granule development and melanization.
Conclusions:
- Intracellular granules are integral to the melanization process in Fonsecaea pedrosoi.
- The formation of these granules is linked to the development of acidic compartments within the fungal cells.
- This study provides new insights into the intracellular mechanisms of fungal pigment synthesis.
