Antarctica is the coldest, driest, and most isolated continent of our planet. The White Continent can be subdivided in several climatic zones (roughly sub- Antarctic, maritime Antarctic, and continental Antarctic) in which the possibility for life settlement strictly depends on the environmental conditions which gradually become harsher moving from maritime to continental Antarctica and, within the continental Antarctica, moving from the coast to the interior of the continent (Øvstedal and Lewis Smith, 2001). With only two phanerogams occurring at the edges of the continent, Antarctic terrestrial habitats are entirely dominated by lower organisms, including invertebrates, bryophytes, fungi, algae, and diverse prokaryotes. In continental Antarctica no vascular plants are present; the life of terrestrial ecosystems concentrates in the ice-free sites along the coastal areas where lichens, fungi, mosses, and algae grow abundantly; their occurrence decreases towards inland stations where isolated rocks occasionally present epilithic microorganisms, depending on the climate and the rock surface exposition and slope. In the ice-free areas of the McMurdo Dry Valleys (Southern Victoria Land), conditions become even more hostile. There, lichens occasionally colonize sheltered rock surfaces and life mostly withdraws inside porous rocks where milder nanoclimatic conditions are present. These life-forms, named cryptoendolithic, represent the predominant form of colonization of the Antarctic deserts (Friedmann and Ocampo, 1976; Friedmann, 1982; Wierzchos and Ascaso, 2002). The fissures and cracks of granitic rocks from this area are also colonized, by chasmoendolithic organisms (De los Ríos et al., 2004, 2005a, 2007). In these habitats, microbial life apparently meets in rather narrow niches and forms simple or more complex communities.