Fungi in Salterns

Abstract

Salterns provide special living conditions for microorganisms. They are extreme environments because of high concentrations of NaCl and other salts, occasional rapid changes in water activity, low oxygen concentration, and high UV radiation (Brock 1979). It is generally assumed that microbial life in concentrated seawater at the highest salinities is mainly composed of Archaea and Bacteria and one eukaryotic species, the alga Dunaliella salina. Other eukaryotic microorganisms usually appear at lower salinities and are represented by different species of algae and protozoa (Ramos-Cormenzana 1991; Pedros-Alio et al. 2000). Surprisingly, until recently, fungi have not been isolated from natural hypersaline environments (Buchalo et al.1998; GundeCimerman et al. 2000), although xerophilic fungi able to grow on media with low water activities are frequently isolated from food preserved with high concentrations of salt or sugar (Filtenborg et al. 2000). It seems that growth of the few known xerophilic species of food-borne fungi in the presence of high concentrations of the solute is determined primarily by the water activities of the medium and not by the chemical nature of the solute. This explains why only as late as 1975 the term halophilic fungi was introduced for those few xerophilic food-borne species that exhibit superior growth on media with NaCl as controlling solute (Pitt and Hocking 1985). Only a few reports describe the isolation of fungi from natural moderately saline environments such as salt marshes (Newell 1996), saline soil (Guiraud et al.1995) and seawater (Kohlmeyer and Volkmann-Kohlmeyer 1991). Recently, however, we made a novel observation that fungi, representing the only kingdom so far not known to sustain extremely saline conditions, populate salterns nearly saturated with NaCl (Gunde-Cimerman et al. 2000).