Morphometric and densitometric study of the biogenesis of electron-dense granules in Fonsecaea pedrosoi

Fonsecaea pedrosoi is a polymorphic pathogenic fungus, etiological agent of chromoblastomycosis, that synthesizes a melanin-like pigment. Although thi s 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 gr anules with the melanization process in F. pedrosoi. For this, conidial for ms were grown under conditions where melanin was not synthesized. Afterward s, cells were incubated in Hank's medium supplemented with bovine fetal ser um, at 37 degrees C, to stimulate the pigment production. The genesis of cy toplasmic bodies, with different stages of electron density, was demonstrat ed by transmission electron microscopy. The appearance of fungal acidic com partments, visualized by confocal laser scanning microscopy in cells staine d with acridine orange, was time coincident with the formation of electron- dense granules observed by transmission electron microscopy. The quantifica tion of granule numbers as well as morphometric and densitometric studies w ere performed. (C) 1999 Federation of European Microbiological Societies. P ublished by Elsevier Science B.V. All rights reserved.