This study examined the water relations and solute tolerances of eight xerophilic fungi, including six species isolated from salt fish and two newly discovered species. Researchers tested fungal germination and growth on media with controlled water activity (aw) using three different solutes: sodium chloride (NaCl), glucose/fructose, and glycerol. The results revealed distinct physiological adaptations among the fungi tested. Three species—Basipetospora halophila, Polypaecilum pisce, and Exophiala werneckii—demonstrated superior growth on NaCl-containing media and are classified as halophilic fungi, challenging previous assertions that fungi lack halophilism. Aspergillus wentii proved remarkably salt-tolerant, exhibiting the fastest growth of any fungus studied on NaCl media down to 0.82 aw. In contrast, Geomyces sp. was salt-intolerant. The obligately xerophilic Eurotium sp. showed the most extreme water stress tolerance, growing optimally at 0.88-0.84 aw and as low as 0.68 aw, preferring glucose/fructose over salt media. These findings have practical implications for food microbiology, suggesting that glycerol-based media like DG18 may be inadequate for isolating halophilic fungi from salt-containing foods, and alternative media containing salt are recommended.

Key findings

• Basipetospora halophila, Polypaecilum pisce, and Exophiala werneckii are true halophilic fungi, showing enhanced growth specifically on NaCl media compared to other solutes
• Aspergillus wentii exhibits exceptional salt tolerance, displaying the fastest growth of any fungus tested on NaCl-based media down to 0.82 aw
• Eurotium sp. is the most xerophilic fungus studied, with obligate xerophily confined to 0.935-0.68 aw and optimal growth at 0.88-0.84 aw on glucose/fructose media
• Solute type significantly affects highly specialized xerophilic fungi but minimally affects less specialized species like Aspergillus penicilloides
• Glycerol-based isolation media are inadequate for halophilic fungi; salt-containing media are recommended for food samples with high NaCl content