Perchlorates on Mars enhance the bacteriocidal effects of UV light

Jennifer Wadsworth,Charles S Cockell

doi:10.1038/s41598-017-04910-3

Abstract

Perchlorates have been identified on the surface of Mars. This has prompted speculation of what their influence would be on habitability. We show that when irradiated with a simulated Martian UV flux, perchlorates become bacteriocidal. At concentrations associated with Martian surface regolith, vegetative cells of Bacillus subtilis in Martian analogue environments lost viability within minutes. Two other components of the Martian surface, iron oxides and hydrogen peroxide, act in synergy with irradiated perchlorates to cause a 10.8-fold increase in cell death when compared to cells exposed to UV radiation after 60 seconds of exposure. These data show that the combined effects of at least three components of the Martian surface, activated by surface photochemistry, render the present-day surface more uninhabitable than previously thought, and demonstrate the low probability of survival of biological contaminants released from robotic and human exploration missions.

Highlights

Perchlorates have been detected on Mars both in-situ[1] and inferred in brine seeps[2], which raises questions on their effects on the habitability of that planet
To determine if perchlorate had an effect on cell viability, Bacillus subtilis cells in minimal media M9 were irradiated in the presence of dissolved magnesium perchlorate (Mg(ClO4)2) at a concentration (0.6 wt%) typical of the Martian surface
Oxidants were hypothesized to be on the surface of Mars and responsible for the lack of organics found by the Viking missions[9, 10]

Summary

Introduction

Perchlorates have been detected on Mars both in-situ[1] and inferred in brine seeps[2], which raises questions on their effects on the habitability of that planet. The presence of such salts lowers the freezing point of water[4, 5] thereby potentially allowing for a contemporary active hydrological system on Mars, which could enhance the habitability of the near-surface environment. This has prompted recent research into the use of perchlorates as a potential energy source for bacteria on Mars[6, 7]. In 2008, the NASA Phoenix Lander’s onboard Wet Chemistry Lab eventually discovered the presence of perchlorate anions, at a concentration of 0.4–0.6 wt%1 This finding was recently supported by the Sample Analysis at Mars instrument (SAM) on the Curiosity rover[14]. We report the significant bacteriocidal effects of UV-irradiated perchlorate on life at ambient temperatures and under Martian conditions

Methods

Results

Conclusion