The fine structure of microconidial germination and vegetative cells of Histoplasma capsulatum

Aspects of the fine structure of germinating microconidia (spore less than 5 micron in diameter) and vegetative hyphal cells of Histoplasma capsulatum were examined by electron microscopy. When grown on a soil extract medium, three strains produced masses of smooth-walled conidia when the conidia were examined by light microscopy. Electron microscopy showed the presence of short tuberculations arising as part of the outer layer of the microconidial wall. Within 48 h of incubation at 25 degrees C, germination was initiated by the emergence of a short germ tube whose wall was derived from an inner layer(s) of the cell wall of the germinant. Germ tube formation was occasionally multipolar. Following the initiation of germination, organeller migration and septation, the microcondium rapidly lost its morphological identity. The cytoplasm of the vegetative hyphal cell was observed to contain typical fungal organelles. The septal area was characteristic of that of a ascomycetous fungus.