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Changes in membrane fluidity modulate heat shock gene expression and produced attenuated strains in the dimorphic
1International Institute of Genetics and Biophysics, Naples, Italy.
Abstract:
In the dimorphic fungus Histoplasma capsulatum the expression of heat shock genes is modulated by addition of fatty acids. Addition at 25 degrees C of saturated fatty acid (palmitic acid) to mycelia of H. capsulatum induced a significant increase in heat shock mRNAs transcription when cells were heat shocked. Conversely, treatments with unsaturated fatty acid (oleic acid) drastically reduced the level of heat shock gene transcription at 37 degrees C, and no detectable levels were measurable with 2 mM. Addition of saturated fatty acid induced a thermotolerant state and mitochondria retained ATPase activity coupled to electron transport under severe heat shock conditions and shortened the time required for mycelium-to-yeast phase transition. Conversely, addition of unsaturated fatty acids uncoupled mitochondrial electron transport and prolonged considerably the time required for phase transition at the same temperatures. A virulent strain, if treated with unsaturated fatty acid under condition in which no heat shock was detectable, lost its virulence probably as a consequence of decreased ability to adapt to the new living condition present in the host.
Insights
Saturated fatty acids enhance heat shock gene expression and thermotolerance in Histoplasma capsulatum, promoting faster phase transitions. Unsaturated fatty acids reduce heat shock response and virulence, impacting fungal adaptation.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- Histoplasma capsulatum is a dimorphic fungus.
- Gene expression in H. capsulatum is influenced by environmental factors.
- Fatty acids play roles in cellular processes.
Purpose of the Study:
- To investigate the effect of saturated and unsaturated fatty acids on heat shock gene expression in H. capsulatum.
- To determine how fatty acids influence thermotolerance and mitochondrial function during heat shock.
- To assess the impact of fatty acids on the dimorphic transition and virulence of H. capsulatum.
Main Methods:
- Treatment of H. capsulatum mycelia with palmitic acid (saturated) and oleic acid (unsaturated) at different temperatures.
- Measurement of heat shock mRNAs transcription levels.
- Assessment of mitochondrial ATPase activity and electron transport.
- Evaluation of mycelium-to-yeast phase transition time.
- Virulence assays of fatty acid-treated strains.
Main Results:
- Saturated fatty acid (palmitic acid) increased heat shock mRNA transcription and induced thermotolerance.
- Unsaturated fatty acid (oleic acid) reduced heat shock gene transcription and uncoupled mitochondrial electron transport.
- Saturated fatty acids shortened the phase transition time, while unsaturated fatty acids prolonged it.
- Unsaturated fatty acid treatment reduced the virulence of H. capsulatum.
Conclusions:
- Fatty acid composition significantly modulates heat shock response, thermotolerance, and dimorphic transition in H. capsulatum.
- Saturated fatty acids promote adaptation to heat stress, whereas unsaturated fatty acids impair it.
- Alterations in fatty acid metabolism can affect the virulence of H. capsulatum by impacting its adaptive capabilities.