title: Characterisation of Growth and Ultrastructural Effects of the Xanthoria elegans Photobiont After 1.5 Years of Space Exposure on the International Space Station.
abstract: The lichen Xanthoria elegans has been exposed to space and simulated Mars-analogue environment in the Lichen and Fungi Experiment (LIFE) on the EXPOSE-E facility at the International Space Station (ISS). This long-term exposure of 559 days tested the ability of various organisms to cope with either low earth orbit (LEO) or Mars-analogue conditions, such as vacuum, Mars-analogue atmosphere, rapid temperature cycling, cosmic radiation of up to 215 ± 16 mGy, and insolation of accumulated doses up to 4.87 GJm(-2), including up to 0.314 GJm(-2) of UV irradiation. In a previous study, X. elegans demonstrated considerable resistance towards these conditions by means of photosynthetic activity as well as by post-exposure metabolic activity of 50-80% in the algal and 60-90% in the fungal symbiont (Brandt et al. Int J Astrobiol 14(3):411-425, 2015). The two objectives of the present study were complementary: First, to verify the high post-exposure viability by using a qualitative cultivation assay. Second, to characterise the cellular damages by transmission electron microscopy (TEM) which were caused by the space and Mars-analogue exposure conditions of LIFE. Since the algal symbiont of lichens is considered as the more susceptible partner (de Vera and Ott 2010), the analyses focused on the photobiont. The study demonstrated growth and proliferation of the isolated photobiont after all exposure conditions of LIFE. The ultrastructural analysis of the algal cells provided an insight to cellular damages caused by long-term exposure and highlighted that desiccation-induced breakdown of cellular integrity is more pronounced under the more severe space vacuum than under Mars-analogue atmospheric conditions. In conclusion, desiccation-induced damages were identified as a major threat to the photobiont of X. elegans. Nonetheless, a fraction of the photobiont cells remained cultivable after all exposure conditions tested in LIFE.
authors.affiliation: Institute of Botany, Heinrich-Heine-University (HHU), Universitaetsstr. 1, 40225, Duesseldorf, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Brandt
authors.affiliation: Institute of Botany, Heinrich-Heine-University (HHU), Universitaetsstr. 1, 40225, Duesseldorf, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Posthoff
authors.affiliation: Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, 12489, Berlin, Germany.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: de Vera
authors.affiliation: Department of Ecological and Biological Sciences (DEB), Tuscia University, Largo dell'Università, 01100, Viterbo, Italy.
authors.forename: Silvano
authors.initials: S
authors.lastname: Onofri
authors.affiliation: Institute of Botany, Heinrich-Heine-University (HHU), Universitaetsstr. 1, 40225, Duesseldorf, Germany. otts@uni-duesseldorf.de.
authors.forename: Sieglinde
authors.initials: S
authors.lastname: Ott
mesh_terms: D001272:Atmosphere / Q000032:analysis*; D003359:Cosmic Radiation; D018534:Earth, Planet; D018559:Exobiology; D005118:Extraterrestrial Environment; D006801:Humans; D008011:Lichens / Q000502:physiology / Q000528:radiation effects*; D018535:Mars; D010788:Photosynthesis / Q000528:radiation effects*; D018561:Space Simulation; D018531:Spacecraft; D014466:Ultraviolet Rays
keywords: Astrobiology; Expose-E; Lichen; Life; Mars-analogue conditions; Space conditions