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Applied and Environmental Microbiology, February 2008, p. 959-970, Vol. 74, No. 4
0099-2240/08/$08.00+0     doi:10.1128/AEM.01973-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Effect of Shadowing on Survival of Bacteria under Conditions Simulating the Martian Atmosphere and UV Radiation{triangledown} ,{dagger}

Shariff Osman,1 Zan Peeters,2 Myron T. La Duc,1 Rocco Mancinelli,3 Pascale Ehrenfreund,2 and Kasthuri Venkateswaran1*

Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109,1 Leiden Institute of Chemistry, Astrobiology Laboratory, 2300 RA Leiden, The Netherlands,2 Carl Sagan Center, SETI Institute, Mountain View, California 940433

Received 28 August 2007/ Accepted 4 December 2007

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-µm-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-µm-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 (~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.

* Corresponding author. Mailing address: Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 89, 4800 Oak Grove Dr., Pasadena, CA 91109. Phone: (818) 393-7245. Fax: (818) 393-4176. E-mail: kjvenkat{at}jpl.nasa.gov

{triangledown} Published ahead of print on 14 December 2007.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, February 2008, p. 959-970, Vol. 74, No. 4
0099-2240/08/$08.00+0     doi:10.1128/AEM.01973-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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