title: The Effect of High-Dose Ionizing Radiation on the Isolated Photobiont of the Astrobiological Model Lichen Circinaria gyrosa.
abstract: Lichen symbioses between fungi and algae represent successful life strategies to colonize the most extreme terrestrial habitats. Consequently, space exposure and simulation experiments have demonstrated lichens' high capacity for survival, and thus, they have become models in astrobiological research with which to discern the limits and limitations of terrestrial life. In a series of ground-based irradiation experiments, the STARLIFE campaign investigated the resistance of astrobiological model organisms to galactic cosmic radiation, which is one of the lethal stressors of extraterrestrial environments. Since previous studies have identified that the alga is the more sensitive lichen symbiont, we chose the isolated photobiont Trebouxia sp. of the astrobiological model Circinaria gyrosa as a subject in the campaign. Therein, γ radiation was used to exemplify the deleterious effects of low linear energy transfer (LET) ionizing radiation at extremely high doses up to 113 kGy in the context of astrobiology. The effects were analyzed by chlorophyll a fluorescence of photosystem II (PSII), cultivation assays, live/dead staining and confocal laser scanning microscopy (CLSM), and Raman laser spectroscopy (RLS). The results demonstrate dose-dependent impairment of photosynthesis, the cessation of cell proliferation, cellular damage, a decrease in metabolic activity, and degradation of photosynthetic pigments. While previous investigations on other extraterrestrial stressors have demonstrated a high potential of resistance, results of this study reveal the limits of photobiont resistance to ionizing radiation and characterize γ radiation-induced damages. This study also supports parallel STARLIFE studies on the lichens Circinaria gyrosa and Xanthoria elegans, both of which harbor a Trebouxia sp. photobiont. Key Words: Astrobiology-Gamma rays-Extremotolerance-Ionizing radiation-Lichens-Photobiont. Astrobiology 17, 154-162.
authors.affiliation: 1 Institute of Botany, Heinrich-Heine-University (HHU) , Düsseldorf, Germany .
authors.forename: Joachim
authors.initials: J
authors.lastname: Meeßen
authors.affiliation: 1 Institute of Botany, Heinrich-Heine-University (HHU) , Düsseldorf, Germany .
authors.forename: Theresa
authors.initials: T
authors.lastname: Backhaus
authors.affiliation: 1 Institute of Botany, Heinrich-Heine-University (HHU) , Düsseldorf, Germany .
authors.forename: Annette
authors.initials: A
authors.lastname: Brandt
authors.affiliation: 2 Space Microbiology Research Group, Radiation Biology Department, Institute of Aerospace Medicine , German Aerospace Center (DLR), Cologne, Germany .
authors.forename: Marina
authors.initials: M
authors.lastname: Raguse
authors.affiliation: 3 Institute of Optical Sensor Systems , German Aerospace Center (DLR), Berlin, Germany .
authors.forename: Ute
authors.initials: U
authors.lastname: Böttger
authors.affiliation: 4 Institute of Planetary Research , German Aerospace Center (DLR), Berlin, Germany .
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: de Vera
authors.affiliation: 5 Departamento de Observación de la Tierra, Instituto Nacional de Técnica Aeroespacial (INTA) , Madrid, Spain .
authors.forename: Rosa
authors.initials: R
authors.lastname: de la Torre
mesh_terms: D002734:Chlorophyll / Q000032:analysis; D000077194:Chlorophyll A; D004307:Dose-Response Relationship, Radiation; D018559:Exobiology; D005453:Fluorescence; D007834:Lasers; D008011:Lichens / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D008954:Models, Biological; D010788:Photosynthesis / Q000528:radiation effects; D011839:Radiation, Ionizing; D013059:Spectrum Analysis, Raman
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A