Abstract
The filamentous fungus Aspergillus niger is one of the main contaminants of the International Space Station (ISS). It forms highly pigmented, airborne spores that have thick cell walls and low metabolic activity, enabling them to withstand harsh conditions and colonize spacecraft surfaces. Whether A. niger spores are resistant to space radiation, and to what extent, is not yet known. In this study, spore suspensions of a wild-type and three mutant strains (with defects in pigmentation, DNA repair, and polar growth control) were exposed to X-rays, cosmic radiation (helium- and iron-ions) and UV-C (254 nm). To assess the level of resistance and survival limits of fungal spores in a long-term interplanetary mission scenario, we tested radiation doses up to 1000 Gy and 4000 J/m2. For comparison, a 360-day round-trip to Mars yields a dose of 0.66 ± 0.12 Gy. Overall, wild-type spores of A. niger were able to withstand high doses of X-ray (LD90 = 360 Gy) and cosmic radiation (helium-ion LD90 = 500 Gy; and iron-ion LD90 = 100 Gy). Drying the spores before irradiation made them more susceptible toward X-ray radiation. Notably, A. niger spores are highly resistant to UV-C radiation (LD90 = 1038 J/m2), which is significantly higher than that of other radiation-resistant microorganisms (e.g., Deinococcus radiodurans). In all strains, UV-C treated spores (1000 J/m2) were shown to have decreased biofilm formation (81% reduction in wild-type spores). This study suggests that A. niger spores might not be easily inactivated by exposure to space radiation alone and that current planetary protection guidelines should be revisited, considering the high resistance of fungal spores.
Highlights
Radiation is the most challenging factor for life in the space environment (Horneck et al, 2010; Chancellor et al, 2014)
Whereas indirect damage is induced by the generation of reactive oxygen species (ROS) – which are produced by the interaction of radiation with cellular water molecules in a process called radiolysis (Cadet et al, 2015; Moeller et al, 2017)
Spores from the wild-type, color mutant and non-homologous end-joining (NHEJ) mutant strains were exposed to different X-ray doses
Summary
Radiation is the most challenging factor for life in the space environment (Horneck et al, 2010; Chancellor et al, 2014). Aspergillus niger Radiation galactic cosmic radiation (GCR) (Chancellor et al, 2018). Radiation shielding on the International Space Station (ISS) is provided by both the Earth’s magnetosphere and the walls of the space station. Due to the absence of Earth’s magnetosphere, space missions toward the Moon or Mars will be exposed to substantially higher radiation doses than those currently experienced on the ISS (Cucinotta et al, 2013; Chancellor et al, 2014, 2018; Narici et al, 2017). Studies on how radiation affects cells have identified two main types of damage: direct and indirect. Whereas indirect damage is induced by the generation of reactive oxygen species (ROS) – which are produced by the interaction of radiation with cellular water molecules in a process called radiolysis (Cadet et al, 2015; Moeller et al, 2017)
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