Abstract
The purpose of this study was to determine survivability of Escherichia coli, Deinococcus radiodurans and Paraburkholderia fungorum under Mars-simulated conditions for freeze-thawing (−80 °C to +30 °C) and UV exposure alone and in combination. E. coli ATCC 25922, D. radiodurans and P. fungorum remained viable following 20 successive freeze-thaw cycles, exhibiting viabilities of 2.3%, 96% and 72.6%, respectively. E. coli ATCC 9079 was non-recoverable by cycle 9. When exposed to UV irradiation, cells withstood doses of 870 J/m2 (E. coli ATCC 25922), 200 J/m2 (E. coli ATCC 9079), 50,760 J/m2 (D. radiodurans) and 44,415 J/m2 (P. fungorum). Data suggests P. fungorum is highly UV-resistant. Combined freeze-thawing with UV irradiation showed freezing increased UV resistance in E. coli ATCC 25922, E. coli DSM 9079 and D. radiodurans by 6-fold, 30-fold and 1.2-fold, respectively. Conversely, freezing caused P. fungorum to exhibit a 1.75-fold increase in UV susceptibility. Strain-dependent experimentation demonstrated that freezing increases UV resistance and prolongs survival. These findings suggest that exposure to short wavelength UV rays (254 nm) and temperature cycles resembling the daily fluctuating conditions on Mars do not significantly affect survival of D. radiodurans, P. fungorum and E. coli ATCC 25922 following 20 days of exposure.
Highlights
E. coli strains were incubated at 37 ◦ C for 18 h, and P. fungorum and D. radiodurans were incubated at 30 ◦ C for 48 h
Plates were incubated at 37 ◦ C for 24 h (E. coli) and 30 ◦ C for h (P. fungorum and D. radiodurans)
Both E. coli strains were incubated at 37 °C for 18 h while P. fungorum and D. Both E. coli strains were incubated at 37 ◦ C for 18 h while P. fungorum and D. radiodurans radiodurans were incubated at 30 °C for 48 h; all colony forming unit counts were were incubated at 30 ◦ C for 48 h; all colony forming unit counts were enumerated
Summary
Over the course of one Martian day (24.65 h), surface temperatures on Mars can vary depending on the location and the reporting source [1,2]. Present-day Mars has UV wavelengths ranging from 200–400 nm, which is comparable to the surface wavelengths that reach Earth (290–400 nm) [4]. The UV radiation environment on Mars features shorter wavelengths within the UVC (200–280 nm) and UVB (280–315 nm) spectra, with UVC being biologically damaging due to its DNA disrupting capabilities [5]. This occurs as UVC energy is absorbed by DNA causing the dimerization of nucleic acid bases including cyclobutane pyrimidine species and pyrimidine (6–4) pyrimidone compounds, together with their
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