Effects of a simulated Martian UV flux on the cyanobacterium, Chroococcidiopsis sp. 029

Cockell, Charles S.; Schuerger, Andrew C.; Billi, Daniela; Friedmann, E. Imre; Panitz, Corinna. 2005 Effects of a simulated Martian UV flux on the cyanobacterium, Chroococcidiopsis sp. 029. Astrobiology, 5 (2). 127-140. 10.1089/ast.2005.5.127

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Abstract/Summary

Dried monolayers of Chroococcidiopsis sp. 029, a desiccation-tolerant, endolithic cyanobacterium, were exposed to a simulated martian-surface UV and visible light flux, which may also approximate to the worst-case scenario for the Archean Earth. After 5 min, there was a 99% loss of cell viability, and there were no survivors after 30 min. However, this survival was approximately 10 times higher than that previously reported for Bacillus subtilis. We show that under 1 mm of rock, Chroococcidiopsis sp. could survive (and potentially grow) under the high martian UV flux if water and nutrient requirements for growth were met. In isolated cells, phycobilisomes and esterases remained intact hours after viability was lost. Esterase activity was reduced by 99% after a 1-h exposure, while 99% loss of autofluorescence required a 4-h exposure. However, cell morphology was not changed, and DNA was still detectable by 4',6-diamidino-2-phenylindole staining after an 8-h exposure (equivalent to approximately 1 day on Mars at the equator). Under 1 mm of simulant martian soil or gneiss, the effect of UV radiation could not be detected on esterase activity or autofluorescence after 4 h. These results show that under the intense martian UV flux the morphological signatures of life can persist even after viability, enzymatic activity, and pigmentation have been destroyed. Finally, the global dispersal of viable, isolated cells of even this desiccation-tolerant, ionizing-radiation-resistant microorganism on Mars is unlikely as they are killed quickly by unattenuated UV radiation when in a desiccated state. These findings have implications for the survival of diverse microbial contaminants dispersed during the course of human exploratory class missions on the surface of Mars.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1089/ast.2005.5.127
Programmes:	BAS Programmes > Antarctic Science in the Global Context (2000-2005) > Life at the Edge - Stresses and Thresholds
ISSN:	1531-1074
Additional Keywords:	Cyanobacteria, Ultraviolet, Astrobiology
NORA Subject Terms:	Biology and Microbiology
Date made live:	19 Dec 2007 15:29 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/1705

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