| Summary: | Permafrost can be defined soil material which lies at temperature below 0 °C for at least two years due to a continuously frozen state. The depth of permafrost table is variable and changes depending on the seasonally temperature. Permafrost table should be not considered as a unique layer, as it is stratified in active layer, talik and brine. Active layer is the portion of soil above the permafrost table. It is called active because its physic status is seasonally modified by thawing and freezing changes, thus becoming active in interconnection with the atmosphere. This layer plays an important role in cold regions because most ecological, hydrological, biogeochemical activities take place within it. This depth varies during different seasons and locations, from 2 cm in the coldest area to 100 cm in the warmer area. Talik is a layer of unfrozen ground in a permafrost area. Talik may have temperatures above 0 °C or below 0 °C. Brines are amounts of liquid water, which is a salt water basin within permafrost table formed during winter season. The brine formation depends on the increase of salt concentration in groundwaters under or behind permafrost, combined to evaporation and halite dissolution processes that generate the formation of veins and pockets of salt liquid that does not frozen under 0 °C. Permafrost is considered as an extreme environment due to its physiochemical features, namely low temperature, oligotrophic nature of sediments and water availability. Microorganisms that live in this environment are generally psychrophiles, which had successfully colonized all cold environments adapting their enzymes to permit them to survive and function in extreme habitats. The study of the permafrost and brine is therefore important to understand microorganism adaptations to extreme environments. For these reasons, the aim of the present Thesis was the study of structure and functions of the prokaryotic communities inhabiting Antarctic permafrost and brines. Permafrost samples were collected during different ...
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