Stress-Induced Cross-Protection and Combined Stress Responses in Extremotolerant Black Yeasts

Area of Science:

• Environmental microbiology
• Fungal extremotolerance
• Stress response in fungi

Background:

• Fungi inhabit diverse environments with multiple overlapping stressors.
• Most studies examine single stress factors, neglecting combined effects.
• Understanding fungal adaptation to combined stresses is crucial for predicting ecological roles.

Purpose of the Study:

• To investigate the impact of preconditioning (salt, cold, or both) on fungal survival after desiccation and freezing.
• To determine if combined salinity and temperature effects on fungal growth are additive or synergistic.
• To explore differential stress tolerance mechanisms in extremotolerant fungi.

Main Methods:

• Studied four fungal species: Aureobasidium pullulans, Aureobasidium subglaciale, Aureobasidium melanogenum, and Hortaea werneckii (haploid and diploid).
• Assessed survival rates after preconditioning treatments followed by desiccation and freezing.
• Analyzed fungal growth under combined salinity and temperature conditions.

Main Results:

• Preconditioning significantly improved desiccation survival in A. pullulans, indicating inducible cross-protection.
• Hortaea werneckii showed less improvement, suggesting a specialist strategy with constitutive tolerance.
• Combined salinity and temperature had synergistic effects on Aureobasidium spp. growth.
• H. werneckii diploid strains exhibited unaffected growth under salinity, supporting adaptation to osmotic stress.

Conclusions:

• Fungal extremotolerance can be achieved through inducible flexibility (Aureobasidium) or constitutive halotolerance (Hortaea werneckii).
• Hybrid diploid genomes in H. werneckii are likely an adaptation to osmotic stress.
• Findings reveal distinct pathways for fungal adaptation to multiple environmental stressors.