Appendix A
Deinococcus radiodurans as an Analogue to Extremophile Organisms That May Have Survived on Mars

Michael J. Daly

Department of Pathology, Uniformed Services University of the Health Sciences, Bethesda, Maryland

The only genetic systems within which the equivalent of millions of years’ worth of background radiation accumulated as genetic damage have been studied in a living organism are those developed by the terrestrial bacterium Deinococcus radiodurans.1-7 This bacterium is capable of repairing massive genetic damage without lethality or increasing mutation frequency. As such, D. radiodurans is an excellent organism in which to consider the potential for survival and biological evolution beyond its planet of origin, as well as the ability of life to survive extremely long periods of metabolic dormancy in high-radiation environments. Ultimately, the survival of any organism in such environments will be determined by its ability to repair, and recover from, accumulated genetic damage. D. radiodurans could likely survive extended periods of metabolic dormancy near the surface of Mars, periods of time in which the equivalent of Mrads of radiation damage would be accumulated in any genetic material.

It is likely that during the first 500 million years (0.5 Ga) of its existence, Mars had a warmer and wetter climate than it has now, and an active hydrologic cycle. This may slightly predate the time at which Earth first began to support water and life; evidence of chemically evolved life on Earth dates to ~0.6 Ga after its formation.


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