Xerophilic fungi occupy versatile environments owing to their rich arsenal helping them successfully adapt to water constraints as a result of low relative humidity, high-osmolarity, and high-salinity conditions. The general term xerophilic fungi relates to organisms that tolerate and/or require reduced water activity, while halophilic and osmophilic are applied to specialized groups that require high salt concentrations or increased osmotic pressure, respectively. Species belonging to the family Aspergillaceae, and especially those classified in Aspergillus subgenus Aspergillus (sections Restricti and Aspergillus) and Polypaecilum, are particularly enriched in the group of osmophilic and salt-tolerant filamentous fungi. They produce an unprecedently wide spectrum of salt tolerant enzymes including proteases, peptidases, glutaminases, γ-glutamyl transpeptidases, various glycosidases such as cellulose-decomposing and starch-degrading hydrolases, lipases, tannases, and oxidareductases. These extremophilic fungi also represent a huge untapped treasure chest of yet-to-be-discovered, highly valuable, biologically active secondary metabolites. Furthermore, these organisms are indispensable agents in decolorizing textile dyes, degrading xenobiotics and removing excess ions in high-salt environments. They could also play a role in fermentation processes at low water activity leading to the preparation of daqu, meju, and tea. Considering current and future agricultural applications, salt-tolerant and osmophilic Aspergilli may contribute to the biosolubilization of phosphate in soil and the amelioration salt stress in crops. Transgenes from halophile Aspergilli may find promising applications in the engineering of salt stress and drought-tolerant agricultural crops. Aspergilli may also spoil feed and food and raise mycotoxin concentrations above the permissible doses and, therefore, the development of novel feed and food preservation technologies against these Aspergillus spp. is also urgently needed. On the other hand, some xerophilic Aspergilli have been shown to be promising biological control agents against mites.
Key points
• Salt tolerant and osmophilic Aspergilli can be found in versatile environments
• These fungi are rich resources of valuable enzymes and secondary metabolites
• Biotechnological and agricultural applications of these fungi are expanding
