Protista is a group of eukaryotic auto- and heterotrophic organisms, rich in the number of species and their diversity. At present, this group amounts, by different estimates, to 120,000-200,000 species; these species are only a minor part of those really existing in nature (Poljansky et al. 2000).

Protozoa is a polyphyletic group of protists, which includes heterotrophic (free-living and parasitic), presumably unicellular organisms. Free-living protozoa are distributed worldwide, and inhabit almost all suitable-for-life environments. In all geographical zones, they are an obligatory component of soil biocenoses, comparable in number and diversity only to bacteria (Poljansky et al. 2000; Auer and Arndt 2001).

Protozoa are able to live over a wide temperature range and to adapt to both extremely high and low temperatures. In cold habitats, the temperature optimum for growth and reproduction of protozoa are lowered (Sukhanova 1968; Lozina-Lozinsky 1972). Owing to their highly developed adaptive strategies, these eukaryotic organisms are widespread in various biotopes of polar regions: in the cold sea and fresh waters, as a component of plankton and benthos (Tong et al. 1997; Robinson 2001; Mylnikov et al. 2002; Petz et al. 2005; De Jonckheere 2006; Petz 2007; Tikhonenkov and Mazei 2007), in the melt water and ice (Ikavalko et al. 1996; Ikavalko 1998), and in the terrestrial ecosystems of the Antarctic and high-latitude Arctic (Smith 1978; Foissner 1996; Petz 1997; Bobrov et al. 2003).

The ability to switch to cryptobiotic stages, i.e., to form resting cysts which are well-developed in soil protozoa, allows them to survive under unfavorable environmental conditions and to spread over sizeable territories (Hausmann and Hulsmann 1996; Clegg 2001). It is known that, in the state of cryptobiosis, they can sustain

Anastassia V. Shatilovich

Institute of Physicochemical and Biological Problems in Soil Sciences, Russian Academy of Sciences, 142290, Pushchino, Moscow Region, Russia [email protected]

R. Margesin (ed.) Permafrost Soils, Soil Biology 16,

DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009

temperatures from -1 to -60°C in natural environments and from -1 to -269°C under experimental conditions (Poljansky et al. 2000). Cases of protozoa cysts have been described that kept viability after long-term (several tens of years) conservation in the ices of Greenland and the Baltic Sea (Ikavalko et al. 1996, Ikavalko and Grandinger 1997; Ikavalko 1998) and in dry soil samples (Goodney 1914; Lozina-Lozinsky 1972; Moon-van der Staay et al. 2006). Cysts of the infusorium Colpoda steinii and amoeba Vahlkampfia sp., which preserved the capabability of excysta-tion after several centuries of cryoconservation (Marquardt et al. 1966), were isolated from the Greenland ice.

There are no data on viable protozoa specimens found in permafrost sediments. In the 1930s, Kapterev reported on finding viable amoebas and ciliates in the Transbaikalian permafrost (Kapterev 1936, 1938). These organisms were, however, probably found at the bottom of the seasonal-thawing layer.

Our investigations have shown that protozoa cysts, conserved in permafrost (at stably low temperatures, in the dark, without water and oxygen), can remain viable for several hundred thousands of years (Shatilovich et al. 2005, 2007; Shatilovich and Petrovskaya 2007; Shmakova et al. 2007; Gilichinsky et al. 2007).

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