Bacterial spores are a powerful biodosimetric system for environmental monitoring and astrobiological studies both in space flight and ground-based simulations in order to obtain information on the biological damage produced by space conditions. Onboard of several spacecraft (Apollo 161, Spacelab 1, LDEF, ISS), spores of Bacillus subtilis were exposed to selected parameters of space, such as vacuum and different spectral ranges of solar UV-radiation and cosmic rays. The mechanism of ionizing radiation lethality is due to the interaction of charged particles or high-energy electromagnetic radiation with matter to mainly produce excitations and ionizations. The charged particles and ions destroy the integrity of critical cellular targets, resulting in loss of viability. DNA double-strand breaks (DSB) and single-strand breaks (SSB) are major DNA damage induced by exposure to ionizing radiation. Especially, the radiation environment on Earth, in low-Earth orbit, on Mars, and in deep space is typified by a wide variety of primary particles covering an extended range of energies. Galactic cosmic rays (GCR) are charged particles that originate from sources beyond our solar system. The distribution of GCR is believed to be isotropic throughout interstellar space2.
In the dormant state spores remain metabolically inactive, and thus substantial DNA, protein, tRNA and ribosome damage may accumulate and the spores are incapable of repairing and/or degrading such damaged DNA and proteins. Consequently, damage to DNA, proteins or other essential components of bacterial spores poses a unique problem, since such repair of such damage does not occur until the processes of germination and outgrowth, when spores reactivate and prepare to return to vegetative growth. Spores appear to have two possible ways to minimize deleterious effects of ionizing radiation: (i) by protecting dormant spore macromolecules (in particular the spore DNA) from damage in the first place and (ii) by ensuring detoxification and repair of direct and indirect damage during spore germination3. Here, I would present an overview of our current understanding on the factors involved in the B. subtilis spore resistance to ionizing radiation.

References:
1 Bucker et al. (1973) Life Sci. Space Res., Vol. 11, p. 295-305.
2 Reitz (2008) Z. Med. Phys., Vol. 18, p. 233-243.
3 Moeller et al. (2014) Appl. Environ. Microbiol., Vol. 80, p. 104-109.