Some bacteria have the survival ability under conditions that are commonly considered as extreme, for instance in environments experiencing high pressure or high salt concentrations, or high doses of irradiation. In our experiments, we were studying a bacterium that live in the saturated concentration of salt called extreme halophilic archaea. This archaebacterium belongs to the genus Halobacterium. In nature, this species is under high doses of UV radiation of sunlight that cause DNA damage in this bacterium, and in order to survive they probably possess efficient DNA-repair mechanisms. Ionizing radiation causes similar types of DNA damage including double-strand breaks, which are the most deleterious to the organism. We also studied on DNA repair enzyme in a very high radio-resistant bacterium called Rubro bacter radiotoleranse.