Insights into the Survival Capabilities of Cryomyces antarcticus Hydrated Colonies after Exposure to Fe Particle Radiation

Abstract

The modern concept of the evolution of Mars assumes that life could potentially have originated on the planet Mars, possibly during the end of the late heavy bombardment, and could then be transferred to other planets. Since then, physical and chemical conditions on Mars changed and now strongly limit the presence of terrestrial-like life forms. These adverse conditions include scarcity of liquid water (although brine solutions may exist), low temperature and atmospheric pressure, and cosmic radiation. Ionizing radiation is very important among these life-constraining factors because it damages DNA and other cellular components, particularly in liquid conditions where radiation-induced reactive oxidants diffuse freely. Here, we investigated the impact of high doses (up to 2 kGy) of densely-ionizing (197.6 keV/µm), space-relevant iron ions (corresponding on the irradiation that reach the uppermost layer of the Mars subsurface) on the survival of an extremophilic terrestrial organism-Cryomyces antarcticus-in liquid medium and under atmospheric conditions, through different techniques. Results showed that it survived in a metabolically active state when subjected to high doses of Fe ions and was able to repair eventual DNA damages. It implies that some terrestrial life forms can withstand prolonged exposure to space-relevant ion radiation.

Keywords: DNA; melanin; metabolically active cells; radiation; radioresistance.

Figure 1

(A) Survival of fungal colonies in liquid media exposed to accelerated Fe ions. (B) Mathematical model of cell survival dose response. The same letters above bars indicate that the values are not statistically significant according to the t test (p ≤ 0.05).

Figure 2

Metabolic activity of fungal cells after 48 h and 72 h rehydration. Striped bars indicate 48 h rehydration; grey bars indicate 72 h rehydration. Pos Ctr = DNA of C. antarcticus colony growth in physiological conditions. The same letters above bars indicate that the values are not statistically significant according to the t test (p ≤ 0.05).

Figure 3

Percentage of intact (grey bars) and damaged cell-membranes (lined bars) measured with PMA assay coupled with qPCR of C. antarcticus exposed to accelerated Fe ions. Pos Ctr = DNA of C. antarcticus colony growth in physiological conditions. The same letters above bars indicate that the values are not statistically significant according to the t test (p ≤ 0.05).

Figure 4

Quantitative PCR of a 939 bp (base pair) target gene (LSU) of C. antarcticus DNA after exposure to Fe ions irradiation. Pos Ctr = DNA of C. antarcticus colony growth in physiological conditions. Statistical analysis as in Figure 1.