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Abstract
Methanogens have been considered models for life on Mars for many years. In order to survive any exposure at the surface of Mars, methanogens would have to endure Martian UVC radiation. In this research, we irradiated hydrated and desiccated cultures of slightly halophilic Methanococcus maripaludis and non-halophilic Methanobacterium formicicum for various time intervals with UVC (254 nm) radiation. The survivability of the methanogens was determined by measuring methane concentrations in the headspace gas samples of culture tubes after re-inoculation of the methanogens into their growth-supporting media following exposure to UVC radiation. Hydrated M. maripaludis survived 24 h of UVC exposure, while in a desiccated condition they endured for 16 h. M. formicicum also survived UVC radiation for 24 h in a liquid state; however, in a desiccated condition, the survivability of M. formicicum was only 12 h. Some of the components of the growth media could have served as shielding agents that protected cells from damage caused by exposure to ultraviolet radiation. Overall, these results suggest that limited exposure (12–24 h) to UVC radiation on the surface of Mars would not necessarily be a limiting factor for the survivability of M. maripaludis and M. formicicum.
Highlights
Mars UV RadiationUltraviolet (UV) flux on a celestial body is one of the significant constraints that affect the evolution of life on that system
The slightly halophilic methanogen, M. maripaludis, while hydrated survived for about 24 h of UVC exposure, while desiccated cells endured for 16 h (Table 1)
We studied the effect of simulated Martian UVC radiation on the survivability of hydrated and desiccated cultures of two methanogens, M. formicicum, a non-halophile, and M. maripaludis, a slight halophile
Summary
Mars UV RadiationUltraviolet (UV) flux on a celestial body is one of the significant constraints that affect the evolution of life on that system. The reason is that Mars lacks a significant global ozone layer and a magnetic field. The ozone layer in the atmosphere absorbs harmful UV radiation of the Sun and prevents it from reaching the surface, and the magnetic field deflects energetic charged particles such as galactic cosmic rays (GCRs) and solar energetic particles (SEPs), and blocks particles from incident on the surface. Before the rise of oxygen and ozone in the Earth atmosphere, life was probably exposed to higher doses of UV radiation than that of the present day Earth [8,9]. UV flux may not be a critical limiting factor for the evolution of life on Mars [10], but the combination of several environmental factors such as low temperature, lack of liquid water, and the presence of oxidizing compounds cause the surface of Mars to be currently inhospitable
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