Introduction

Survival of microorganisms in outer space, such as resistant bacterial endospores, is affected by harsh environmental conditions including microgravity, space vacuum leading to desiccation, wide variations in temperature and a strong radiation component of both galactic and solar origins (Nicholson et al., 2000). Solar extraterrestrial UV radiation is mostly deleterious due to its UV component consisting of genotoxic UVC (200 < λ < 280 nm) and more energetic vacuum–UV photons (140 < λ < 200 nm) that are able to ionize biomolecules but exhibit very low penetrating features. The galactic cosmic radiation (CGR) is composed predominantly of high-energy protons (85%), electrons, α-particles and high-charge (Z) and energy (E) nuclei (HZE). In addition, solar particle radiation that mostly consists of protons with very small amounts of α-particles and HZE ions is emitted during solar wind and erratic solar flares (Nicholson et al., 2000; Cucinotta et al., 2008). UVC and UVB photons (280 < λ < 320 nm) are, in the absence of shielding, the main lethal components of space radiation. However, an efficient protection against molecular effects of UV radiations is likely to occur when spores are embedded in micrometeorites according to the scenario that has been proposed for allowing interplanetary or interstellar transfer of microorganisms (Mileikowsky et al., 2000; Nicholson et al., 2000). In contrast, under the latter conditions, protection of microorganisms against the damaging effects of CGR, and more precisely, of highly penetrating HZE particles, is at best very limited.