Deinococcus radiodurans is one of the most radiation resistant organisms on earth thanks to a combination of multiple mechanisms, including an unusual nucleoid organization. Our goal was to better understand the organization and dynamics of the nucleoids of D. radiodurans and Deinococcus deserti, another radio-resistant bacterium isolated from the Sahara desert. Specifically, my studies focused on the nucleoid-associated proteins (or NAPs) of these bacteria - the most abundant HU proteins and DNA gyrase - as well as a Deinococcus-specific NAP, DdrC. The objective was to elucidate the structure of these proteins, to characterize their interactions with DNA, and to study their effects on the conformation and compaction of plasmid DNA. Through biochemical studies and atomic force microscopy and electron microscopy analyses, we have highlighted significant differences in the mechanisms of compaction and DNA binding used by the different HU proteins of D. radiodurans (DrHU) and D. deserti (DdHU1, DdHU2 and DdHU3). In particular, we have demonstrated a dual role for DrHU in the organization and compaction of plasmid DNA, which can be either condensed or rigidified depending on the concentration of DNAbound DrHU - a dual function that is not conserved in DdHU1, its closest homolog. We also succeeded in producing two forms of the DNA gyrase, an active form that can be used for functional studies, and a second, more stable, but less active form more suitable for structural studies. Finally, our structural studies of DdrC coupled with biochemical and molecular dynamics analyses revealed the structure of DdrC, its oligomerization state, and its mode of binding to DNA. These results suggest that DdrC may be a Deinococcus-specific NAP, playing a key role in nucleoid compaction after irradiation. Together, these studies have provided a better understanding of the molecular mechanisms used by these radio-resistant bacteria to organize and structure their nucleoid and respond efficiently to genotoxic stresses such as irradiation..