Morphometry and stereology of the conversion of thin-walled yeasts to phase I yeast cells of Wangiella dermatitidis

Abstract

Morphometric and stereological analyses of the conversion of thin-walled yeast cells to thick-walled phase I yeast cells of Wangiella dermatitidis were conducted over 15 days of growth. Log phase growth persisted for 48–60 hours and there was no loss in viability up to 15 days. Average cell volume dropped from 23 μm³ on days 1 and 2 to 18 μm³ on days 3 and 4, then increased to 38 μm³ by day 15. Wide confidence limits for measurements of cell volume at each point indicated a very heterogeneous population. Wall thickness increased throughout the growth period with thickness increasing from 0.04 μm to 0.30 μm and the volume fraction from 0.10 to 0.24. Mitochondria and nuclei together made up less than 8% of the cell volume [volume fraction of mitochondria, 0.025 (2.5%) and volume fraction of nuclei, 0.05 (5.0%)]. Volume fractions of both declined over time, as a result of increased cell volume from isotropic growth, although nuclei also may have become smaller. Glycogen was always present and increased to about 18% of the cell volume by day 4 but then decreased to 10% by day 15. Lipid was absent in early log phase cells but made up about 40% of the cell volume by day 15, and is presumably synthesized at the expense of glycogen and from residual sugar. Vacuoles, evident in early log cells (10–20% of the cell volume), declined rapidly and were rare after 8 days.

Key Words:

• dimorphism
• morphometry
• polymorphism
• stereology
• Wangiella