Ultrastructural studies of the mycelium-to yeast transformation of Sporothrix schenckii

Abstract

Fine details of the internal and external morphology of the in vitro mycelial phase (MP) to yeastlike phase (YP) transition of the dimorphic fungal pathogen Sporothrix schenckii are shown in electron micrographs of ultrathin sections. Morphological transformation at the ultrastructural level was observed to occur by direct formation of budlike structures at the tips and along the hyphae and by oidial cell formation. Direct budding of yeast from conidiospores was not observed. Early transitional forms arising by direct blastic action from the MP possessed conspicuous electron-dense microfibrillar material at the outer limits of the cell wall. The electron density of this microfibrillar material was enhanced by staining with acidified dialyzed iron. It is believed that this extracellular material may be composed in part of an acid mucosubstance. No acid phos

Sporothrix schenckii and related species of Ceratocystis.

“…They were apparently included in a matrix of electrontransparent material. The conidial cytoplasm contained large lipid storage bodies which were not found in yeast cells or hyphae (46,206). Young hyphal cells of S. schenckii, C. stenoceras, Ceratocystis pluriannulata, C. ulmi, and C. minor had unusual osmiophilic structures (48).…”

“…Conidia germinate into short hyphae, which in turn give rise to yeast cells. Yeast cells can also arise by fragmentation of chains of oidia, which often occur inside hyphae (46,66).…”

“…The appearance of discrete intracytoplasmic membranes precedes the appearance of the transitional cell type. Transitional forms arising from hyphae by direct budding or by oidial cell formation ( 2) have been observed in S. schenckii (46,84). The claim that yeast cells could also arise by budding from conidia (217) has not been substantiated.…”

Sporothrix schenckii — a freeze‐fracture study

“…The ultrastructural characteristics of both vegetative forms and of conidia have been studied extensively by ultrathin sectioning (LANE et ul. 1969, GARRISON et al 1975, GARRISON et a/. 1982, ARNOLD et al 1987.…”

The effect of temperature on the ultrastructure of Histoplasma capsulatum during the mycelium‐yeast transition

“…Ultrastructural observations have shown alterations in the structure of the cell wall48 h after temperature shift in both H. capsulatum and Sporothrix schenckii. Five d after temperature shift direct budding from hyphal cells and formation of oidial chains after cytoplasmic condensation have been observed [3,4].…”