Molecular systems described for Archaea show primitive and simple characteristics, compared to their homologous eukaryotes. In addition, extremophilic characteristic results in an hyper-robust which makes in vitro manipulation and structural studies much easier. Thus, Archaea represent good models for understanding complex cellular functions, particularly those that involve large molecular machines, such as those involved in proteolysis. My thesis consisted in understanding the resistance mechanisms and the importance of proteolytic systems in the adaptation of halophilic Archaea to environmental stresses. Halophilic Archaea accumulate multi-molar concentrations of KCl / NaCl in their cytosol (3.4M KCl / NaCl 1.1M for Halobacterium Salinarum). This requires a very special biochemistry that allows operation in solvents where free water is scarce. Thus, the proteins of these organisms are themselves halophilic and are soluble and folded only in extreme salinity conditions (2 to 5 M). This particular biochemistry partly explain the extraordinary ability of halophilic Archaea to resist physical and chemical stress (temperature, radiation, dehydration). We study the response of the halophilic Archaea strict H. salinarum at low-salinity stress. Indeed, beyond the osmotic shock, the fall of the environment salt concentration causes a decrease in the intracellular KCl concentration, which should have a direct effect on the folding state of intracellular protein, as in case of heat stress. In the first part of this thesis, a study was conduct to determine viability limits and cytosolic modifications, associated with a salinity decrease. These studies involve intracellular salt dosages, viability studies (microscopic counts, color live / dead), induction of chaperone proteins linked to stress response and biophysical neutron experiments, to evaluate the effect of stress on proteins folding. In this work, a phenomenon of survival at low salinity linked to morphological changes was revealed. To describe this phenomenon, this second study involves confocal microscopy experiences, fluorescence microscopy, viability tests, counting on box, scanning electron microscopy, electron microscopy by negative staining, salt intracellular dosages and proteins separation experiments, to study the overall proteome composition during low salinity stress. In this study, a fall of the intracellular K⁺ concentration and the proteome clarification during stress was revealed. Low salt concentrations causes halophiles proteins denaturation, the accumulation of misfolded proteins in the cytoplasm involves chaperones systems and intracellular proteolysis machinery. In this context, another objective of my thesis was to contribute to the understanding of the intracellular proteolysis role in the PAN-proteasome system and in the aminopeptidase TET complex, in stress conditions established in previous studies. This part of the thesis involves experiments of endopeptidase activity assay, aminopeptidase activity assay, quantification of mRNA genic expression by Northern blot, immunoprecipitation, proteins separation by sucrose gradient and proteasome chemical inhibition (drug). We show the role of the PAN-proteasome system in stress response and we deepen our understanding of the aminopeptidase TET role in vivo. This protease appears to have an independent role of the proteasome complex. The protease TET seems to participate at the amino acids treatment in cells to maintain the metabolic activities in nutritional deficiencies.