xerophilen

Xerophilen, or xerophiles, are organisms that thrive in very dry environments or at low water activity. The term comes from Greek xeros, meaning dry, and philos, meaning loving. In microbiology and mycology, xerophiles are contrasted with xerotolerant organisms, which tolerate dryness but do not require it for growth.

Xerophiles grow where water is scarce. Water activity (aw) measures the availability of free water for metabolism. Many xerophiles require low aw and can grow at values that are unfavorable for many other organisms, sometimes down to around 0.6 or lower, depending on the species. They achieve this through adaptations such as accumulating compatible solutes (for example glycerol, proline or certain sugars), producing protective extracellular polymers, having thick or modified cell walls, and sometimes forming resistant spores or cysts to endure desiccation. Growth is often slower, reflecting the stressed, resource-poor conditions they inhabit.

In fungi, xerophily is well documented. Notable xerophilic genera include Aspergillus and Eurotium, as well as Xeromyces and Wallemia, with species described from dried foods and arid environments. Some xerophilic yeasts also inhabit salted or sugary substrates. In bacteria and algae, xerophily is less extensively described, but several lineages show adaptations that enable survival and growth under low-water conditions.

Habitats typical for xerophiles include desert soils, salt flats, caves, stored dried foods, and air with low humidity. Their presence is relevant to food preservation and spoilage, as xerophilic fungi can colonize dried fruits, grains, and spices and may produce secondary metabolites of concern.