Extremely halophilic bacteria are able to survive in a natural environment exposed to high doses of ultraviolet irradiation. One such organism, Halobacterium cutirubrum, has been characterized to possess an extremely efficient photoreactivation from ultraviolet damage. A population irradiated to 1% survivors can photoreactivate to complete recovery of the original population in less than 1 h of illumination. Inhibition of carotenoid pigments by 10−6 M diphenylamine decreased photoreactivation efficiency. The carotene pigments have been implicated in an energy-transfer role to augment the photoreactivation mechanism