N-129. Comparison of Survival of Spacecraft-Associated Bacteria and Endospores within Two Different Mars Simulation Chambers

M. T. La Duc1, S. Osman1, Z. Peeters2, P. Ehrenfreund2, A. Schuerger3, R. Mancinelli4, K. Venkateswaran1;
1Jet Propulsion Lab., California Inst. of Technology, Pasadena, CA, 2Leiden Institute of Chemistry, Astrobiology Lab., Leiden, NETHERLANDS, 3Univ. of Florida, Kennedy Space Center, FL, 4Carl Sagan Ctr., SETI Inst., Mountain View, CA.

Despite a growing understanding of the limits of life on Earth, much less is known about life’s potential for persisting on the surface of Mars. Most literature addressing this topic is based on laboratory strains, which prevents the planetary protection community from accurately predicting the likelihood of “hardy” microbes enduring Martian conditions. To assess wild-type microbial survival, spacecraft-associated bacterial endospores and non spore-forming bacterial isolates were prepared in Mars soil analog suspensions and tested in a desiccated state within two different simulation chambers. Results address both the shadowing effect of soil particulates on bacterial survival under simulated Martian atmospheric and UV conditions, and differences in survival as a consequence of a particular simulation chamber. 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 perished, whereas similarly prepared cells in 60 μm-filtered desert soil (DS)-microcosms survived the experimental exposures. Of the bacterial cells exposed to simulated Martian conditions, several spacecraft isolates and a well known radiation-resistant Deinococcus strain exhibited elevated resistance to UV254. Their survival indices were comparable to those of DS- and DSE-associated Bacillus pumilus spores. Desiccated DSE-spores survived full Martian UV (200 - 400 nm) for 5 min and were only slightly affected by Martian atmospheric conditions in the absence of UV. Although prolonged UV irradiation (5 min to 12 hours) killed substantial portions of the DSE-spore microcosms (~5 to 6 logs reduction under Martian UV), dramatic spore survival was apparent in DS-spore microcosms. Similar survival indices were observed for bacterial endospores tested in the two different simulation chambers, with a 4-log reduction in survival even after a 1-day diurnal exposure. These data show that the Martian environment coupled with nutrient depletion is effective at killing microbes, with repercussions for managing forward contamination of extra-terrestrial environments.