Salinity stress response of black yeasts isolated from deep-sea sediments of the Gulf of Mexico

Fungi that live in deep-sea sediments experience extreme environmental conditions, yet little is known about how they adapt their growth and metabolism to these stresses. This study explores the morphogenetic and metabolomic responses of three black yeasts-Salinomyces thailandicus, Neophaeotheca triangularis, and N. salicorniae-isolated from deep-sea sediments of the Gulf of Mexico under varying salinities and exposure to the melanin inhibitor pthalide. Each species displays distinct growth adaptations: S. thailandicus shifts from filamentous to yeast-like forms as salinity increases, N. triangularis exhibits the opposite trend, and N. salicorniae remains dimorphic but grows more slowly at high salinities. Phthalide inhibits hyphal development in all three species. An exploratory metabolic analysis, conducted on pooled samples, indicates that metabolomic profiles change with salinity, with fatty acids dominating across species, suggesting membrane remodeling as an adaptation to osmotic stress. N. triangularis uniquely accumulates amino acids and peptides, a response previously reported mainly in plants. Additional metabolites, including aminocyclitols and compounds associated with extracellular polymeric substances, suggest the involvement of uncharacterized adaptive mechanisms contributing to stress protection. These findings advance our understanding of how black yeasts adapt to osmotic stress and provide a foundation for future studies.