Survival of Microorganisms under the Extreme Conditions of the Atacama Desert

Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and ochraceus andcells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23°S and 24°S) in the Atacama Desert for up to 15 months. B. subtilis spores (survival 15%) and A. niger conidia (survival 30%) outlived the other species. The survival of the conidiaand spores species was only slightly poorer than that of thecorresponding laboratory controls. However, the Deinococcus radiodurans cells did not survive the desertexposure, because they are readily inactivated at relativehumidities between 40 and 80% which typically occurduring desert nights. Cellular monolayers of the dry sporesand conidia have in addition been exposed to the full sunlight for up to several hours. The solar fluences causing 63% loss in viability (F₃₇-values) have been determined.These F₃₇-values are compared with those determined atother global locations such as Punta Arenas (53°S), Key Largo (25°N) or Mainz (50°N) during the same season. Thesolar UVB radiation kills even the most resistantmicroorganisms within a few hours due to DNA damages. Thedata are also discussed with respect to possible similaritiesbetween the climatic conditions of the recent Atacama Desertand the deserts of early Mars.