Effect of shadowing on survival of bacteria under conditions simulating the Martian atmosphere and UV radiation.
Spacecraft-associated spores and four non-spore-forming bacterial isolates were prepared in Atacama Desert soil suspensions and tested both in solution and in a desiccated state to elucidate the shadowing effect of soil particulates on bacterial survival under simulated Martian atmospheric and UV irradiation conditions. All non-spore-forming cells that were prepared in nutrient-depleted, 0.2-microm-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-microm-filtered desert soil (DS) microcosms survived such conditions. Among the bacterial cells tested, Microbacterium schleiferi and Arthrobacter sp. exhibited elevated resistance to 254-nm UV irradiation (low-pressure Hg lamp), and their survival indices were comparable to those of DS- and DSE-associated Bacillus pumilus spores. Desiccated DSE-associated spores survived exposure to full Martian UV irradiation (200 to 400 nm) for 5 min and were only slightly affected by Martian atmospheric conditions in the absence of UV irradiation. Although prolonged UV irradiation (5 min to 12 h) killed substantial portions of the spores in DSE microcosms (approximately 5- to 6-log reduction with Martian UV irradiation), dramatic survival of spores was apparent in DS-spore microcosms. The survival of soil-associated wild-type spores under Martian conditions could have repercussions for forward contamination of extraterrestrial environments, especially Mars.
Osman
Shariff
S
Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 89, 4800 Oak Grove Dr., Pasadena, CA 91109, USA.
Peeters
Zan
Z
La Duc
Myron T
MT
Mancinelli
Rocco
R
Ehrenfreund
Pascale
P
Venkateswaran
Kasthuri
K
D003889:Desert Climate; D018535:Mars; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D010316:Particle Size; D012987:Soil / Q000032:analysis*; D018561:Space Simulation; D018531:Spacecraft; D013171:Spores, Bacterial / Q000254:growth & development / Q000528:radiation effects* / Q000648:ultrastructure; D016019:Survival Analysis; D014466:Ultraviolet Rays
D012987:Soil