Survival of microorganisms under the extreme conditions of the Atacama Desert

Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and o chraceus and cells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23 degreesS and 24 degreesS) in the Atacama Des ert for up to 15 months. B. subtilis spores (survival similar to 15%) and A . niger conidia (survival similar to 30%) outlived the other species. The s urvival of the conidia and spores species was only slightly poorer than tha t of the corresponding laboratory controls. However, the Deinococcus radiod urans cells did not survive the desert exposure, because they are readily i nactivated at relative humidities between 40 and 80% which typically occur during desert nights. Cellular monolayers of the dry spores and conidia hav e in addition been exposed to the full sun light for up to several hours. T he solar fluences causing 63% loss in viability (F-37-values) have been det ermined. These F-37-values are compared with those determined at other glob al locations such as Punta Arenas (53 degreesS), Key Largo (25 degreesN) or Mainz (50 degreesN) during the same season. The solar UVB radiation kills even the most resistant microorganisms within a few hours due to DNA damage s. The data are also discussed with respect to possible similarities betwee n the climatic conditions of the recent Atacama Desert and the deserts of e arly Mars.