Mycelium-yeast transition in Histoplasma capsulatum. Early ultrastructural changes

Area of Science:

• Mycology
• Cell Biology
• Fungal Pathogenesis

Background:

• Dimorphic fungi, like Histoplasma capsulatum, can switch between mycelial and yeast forms.
• This transition is crucial for fungal survival and pathogenesis.
• Understanding the early stages of this transition is key to controlling fungal infections.

Purpose of the Study:

• To investigate the ultrastructural changes during the initial 24 hours of the mycelium-to-yeast transition in Histoplasma capsulatum.
• To correlate morphological alterations with physiological changes during this critical developmental stage.

Main Methods:

• Histoplasma capsulatum was subjected to a temperature shift to induce the mycelium-to-yeast transition.
• Ultrastructural analysis using electron microscopy was performed at various time points within the first 24 hours.
• Physiological parameters such as respiratory rate and ATP concentration were monitored.

Main Results:

• A significant decrease in respiratory rate, ATP, and cytochrome concentration was observed within 24 hours.
• Ultrastructural changes included plasma membrane undulation, loss of the outer fibrous cell wall layer, and mitochondrial structural disorganization.
• By 24 hours, 70% of cells underwent lysis, with remaining cells showing altered cytoplasmic structures and few mitochondria.

Conclusions:

• The observed ultrastructural changes represent the morphological manifestation of early physiological events during the mycelium-to-yeast transition.
• These findings provide insights into the complex cellular reprogramming required for fungal dimorphism and potential therapeutic targets.