Perchlorates on Mars enhance the bacteriocidal effects of UV light

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.

Extreme salinity as a challenge to grow potatoes under Mars-like soil conditions: targeting promising genotypes

“…Thus, some studies have positive implications showing these minerals as possible electron acceptors by microorganisms capable to provide energy for growth or as powerful antioxidants protecting plants against Mars' harsh environmental stresses and boost the rate of decomposition of organic matter (Bohle et al 2016). On the contrary, other studies show the Martian salts as a detrimental condition for life survival (Wadsworth & Cockell 2017). The presence of different living beings in extreme salt condition on Earth such as the halophilic organisms encourage the options to generate future crops and better understand the mechanisms of survival in these conditions.…”

“…Indeed, Martian regolith has high presence of different types of salts and evaporitic minerals i.e. formed by the evaporation from bodies of water (Vaniman et al 2004;Ewing et al 2006) and they have been detected on Mars both in situ and remotely by different monitoring instruments (Wadsworth & Cockell 2017). The controversy about their effects on the habitability of that planet is still under research.…”

Dried Biofilms of Desert Strains of Chroococcidiopsis Survived Prolonged Exposure to Space and Mars-like Conditions in Low Earth Orbit

“…If carried, for instance, by winds at 5 m$s -1 (Gomez-Elvira et al, 2014) with the average flux mentioned above, they could travel more than 100 km without dying. However, other factors found on Mars need to be taken into account so as to reduce the planetary protection risk, such as the presence of perchlorates that have been shown to be highly damaging to life (Wadsworth and Cockell, 2017).…”

Next Steps Forward in Understanding Martian Surface and Subsurface Chemistry

“…Many of these oxidants are known to be destructive to organic molecules and may contribute to the paucity of organics so far detected on Mars. One recent study has also shown that the presence of perchlorate and hydrogen peroxide can substantially increase the rate of cell death over and above the rate caused by UV radiation alone (Wadsworth & Cockell, 2017). One uncertainty that remains is the depth to which these reactions take place in the subsurface.…”