Introduction

Certain species of fungi, one of the ecologically most successful eukaryotic lineages, can be considered as rare examples of eukaryotic extremophiles. Although they display different adaptive strategies from those encountered in prokaryotic extremophiles (Gunde-Cimerman et al., 2005), they have been isolated from similar extreme environments as bacteria. Fungi have been isolated from hypersaline waters (Gunde-Cimerman et al., 2000), at 10 km depth below the surface of the oceans (Nagahama et al., 2001), from extremely acidic mine waters (Hölker et al., 2004), and from the surface of rocks in arid and cold climates (Gorbushina et al., 1996; Sterflinger and Krumbein, 1997; Sterflinger et al., 1999) as well as in extremely cold polar environments. Cold-tolerant species have been primarily reported in connection with subArctic vegetation (Fisher et al., 1995; Babjeva and Reshetova, 1998; Tosil et al., 2002), in snow and below snow-covered tundra (Vishniac, 1993; Babjeva and Reshetova, 1998; Pennisi, 2003; Schadt et al., 2003), and in permafrost (Dmitriev et al., 1997; Babjeva and Reshetova, 1998; Golubev, 1998; Soinam et al., 2000; Tosil et al., 2002) and offshore polar waters (Broady and Weinstein, 1998). Very few studies describe their presence in Arctic glaciers. Viable fungi have, however, been isolated from Arctic and Antarctic ice, ranging in age from 10,000 and up to 140,000 years (Abyzov, 1993; Ma et al., 1999; Christner et al., 2000; Ma et al., 2000; Poglazova et al., 2001; Christner et al., 2003; Ma et al., 2005).

Glacial ice in polar regions has been thus regarded for long only as a life-preserving medium, chronologically entrapping deposited microbes, transported with atmospheric circulation. A new glacial habitat for active microbial life has been only recently discovered at the base of polythermal glaciers, where ice melting occurs due to changes in pressure. These environments were previously considered abiotic, but recent investigations have shown that they provide a habitat for nonphotosynthetic microorganisms and may constitute a significant global reservoir of biological activity (Skidmore et al., 2000; Foght et al., 2004). Subglacial bacterial populations were found in Northern and Southern hemispheres and beneath high and low altitude glaciers (Skidmore et al., 2000; Foght et al., 2004). Until our investigations, there were no reports on the presence of fungi or any other eukaryotic organism in subglacial ice.

We undertook a study involving the isolation of fungi from an Arctic coastal environment in Spitzbergen, Norway. By choosing appropriate selective isolation conditions our preliminary investigations of randomly sampled glacier ice revealed that fungi are occasionally present in high numbers (Gunde-Cimerman et al., 2003). These results prompted us to focus on the systematic isolation and identification of fungi from different layers of polythermal glaciers.

Herein we present the review of fungal diversity and spatial distribution along glacier layers from four different high Arctic polythermal glaciers (Svalbard, Norway), with emphasis on fungal presence in the unique subglacial environment.

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