Abstract
Extremophiles are optimal models in experimentally addressing questions about the effects 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, until 1000 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 He irradiation better, whereas they were more sensitive to Fe irradiation (until 500 Gy), with spores from thermophiles being more resistant to irradiations than psychrotolerants. The survived spores showed different germination kinetics, depending on the type/dose of irradiation and the germinant used. After exposure to He 1000 Gy, D-glucose increased the lag time of thermophilic spores and induced germination of psychrotolerants, whereas L-alanine and L-valine increased the germination efficiency, except alanine for A43. FTIR spectra showed important modifications to the structural components of spores after Fe irradiation at 250 Gy, which could explain the block in spore germination, whereas minor changes were observed after He radiation that could be related to 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 different contexts, including astrobiology.
Highlights
The boundary conditions of life on Earth have been tested in different possible directions, encompassing the limits of temperature, pH, pressure, salinity, nutrients, and radiations
Spores were resistant to He irradiation until 1000 Gy, with thermophiles SBP3 and T14 being more resistant (LD90 = 404 ± 12 and 386 ± 18 Gy, respectively) than psychrotolerants A34 and A43 (LD90 = 332 ± 15 and 346 ± 12 Gy, respectively); the thermophilic SBP3 strain showed the most robust spore resistance to irradiation with He ions (Figure 1A)
The HZE ions irradiation resistance of poly-extremophilic bacilli spores from hot and cold environments was investigated, resulting in modifications to structural components of spores and how those modifications influence the germination process. Spores survived He irradiation until the highest dose, whereas they were drastically reduced at Fe ions, which are known to present more lethal effects to spores than He nuclei
Summary
The boundary conditions of life on Earth have been tested in different possible directions, encompassing the limits of temperature, pH, pressure, salinity, nutrients, and radiations. A great variety of terrestrial environments exhibit extremes in one or more physical or chemical conditions. This is the case for both marine hydrothermal vents (shallow and deep-sea vents) and polar (Arctic and Antarctic) areas, where microbial (poly) extremophiles are generally the most abundant life forms [1,2,3,4,5]. Poly-extremophiles are important tools for research in different disciplines, spanning from adaptations to harsh conditions [6], with implications for both the origin of life on Earth [7]. Several studies have reported the survival and growth of microorganisms under laboratory-simulated extraterrestrial environments, such as under Enceladus-like and Mars-like conditions [11,17,18]
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