Effects of heavy ion particle irradiation on spore germination of Bacillus spp. from extremely hot and cold environments

Extremophiles are optimal models in experimentally addressing questions about theeffects of cosmic radiation on biological systems. The resistance to high charge energy (HZE)particles, and helium (He) ions and iron (Fe) ions (LET at 2.2 and 200 keV/µm, respectively, until1000 Gy), of spores from two thermophiles, Bacillus horneckiae SBP3 and Bacillus licheniformis T14,and two psychrotolerants, Bacillus sp. A34 and A43, was investigated. Spores survived Heirradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with sporesfrom thermophiles being more resistant to irradiations than psychrotolerants. The survived sporesshowed different germination kinetics, depending on the type/dose of irradiation and the germinantused. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores andinduced germination of psychrotolerants, whereas L-alanine and L-valine increased thegermination efficiency, except alanine for A43. FTIR spectra showed important modifications to thestructural components of spores after Fe irradiation at 250 Gy, which could explain the block inspore germination, whereas minor changes were observed after He radiation that could be relatedto the increased permeability of the inner membranes and alterations of receptor complex structures.Our results give new insights on HZE resistance of extremophiles that are useful in differentcontexts, including astrobiology.