Effect of Shadowing on Survival of Bacteria under Conditions Simulating the Martian Atmosphere and UV Radiation

Abstract

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-m-filtered desert soil (DSE) microcosms and desiccated for 75 days on aluminum died, whereas cells prepared similarly in 60-m-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 (ϳ5-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.

Effects of Simulated Mars Conditions on the Survival and Growth of Escherichia coli and Serratia liquefaciens

“…The current study provides evidence that Escherichia coli, a potential spacecraft contaminant (44,53), may survive but not grow on the surface of Mars. Results suggest that desiccation, UV irradiation, high salinity, and low pressure (in decreasing order of importance) were factors in reducing the number of viable E. coli cells over the course of the 7-day Mars simulations, consistent with related studies on microbial survival under Mars conditions (37,39,47,49,51,52).…”

“…Dispersal mechanisms of viable microbes away from landed or crashed spacecraft on Mars have not been adequately studied and remain significant black boxes in any Mars microbial survival and proliferation model. Long-term survival on Mars is unlikely if microbes are directly exposed to solar UV irradiation (11,37,47,49,50) but likely if the microbes are protected from UV irradiation by thin dust layers or embedded within UV-protected niches in spacecraft (33,39,47). In contrast, the greatest unknown in any Mars microbial survival and proliferation model is whether terrestrial microorganisms found on spacecraft are capable of growth and replication under Mars conditions.…”

“…UV irradiation, especially UVC photons (200 to 280 nm), may be the most biocidal of all factors to microbial survival on the martian surface (34,37,39,47,50,52). Microorganisms found on sun-exposed surfaces of spacecraft are killed off within a few tens of minutes of exposure; but if covered by as little as a few hundred micrometers of martian soil, significant protection is provided (11,34,47).…”

Bio-signature of Ultraviolet-Radiation-Resistant Extremophiles from Elevated Land

“…UVR-resistant microorganisms have shown tremendous stable biotechnological implications [2,3,29,30]. The short exposure of UV is generally known for random mutagenesis, however microbial reversion may produce unstable mutants with commercially viability.…”

“…UV-C-radiationresistant Arthrobacter sp. and Bacillus pumilus have been isolated from the Atacama Desert, able to withstand 1000 J/m 2 UV-C radiation [30]. Microorganism Brevundimonas sp.…”