Meeßen Joachim, Backhaus Theresa, Brandt Annette, Raguse Marina, Böttger Ute, de Vera Jean-Pierre, de la Torre Rosa
1 Institute of Botany, Heinrich-Heine-University (HHU) , Düsseldorf, Germany .
2 Space Microbiology Research Group, Radiation Biology Department, Institute of Aerospace Medicine , German Aerospace Center (DLR), Cologne, Germany .
Astrobiology. 2017 Feb;17(2):154-162. doi: 10.1089/ast.2015.1453.
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.
真菌与藻类之间的地衣共生关系代表了在最极端陆地栖息地定殖的成功生存策略。因此，太空暴露和模拟实验已证明地衣具有很高的生存能力，所以它们已成为天体生物学研究中的模型，用于辨别地球生命的极限和局限性。在一系列地面辐射实验中，“STARLIFE”活动研究了天体生物学模型生物对银河宇宙辐射的抗性，银河宇宙辐射是外星环境中的致命应激源之一。由于先前的研究已确定藻类是地衣共生体中更敏感的一方，我们选择了天体生物学模型圆卷地卷（Circinaria gyrosa）中分离出的共生光合生物绿藻（Trebouxia sp.）作为该活动的研究对象。在该研究中，γ辐射被用于例证在天体生物学背景下，高达113 kGy的极低传能线密度（LET）电离辐射的有害影响。通过光系统II（PSII）的叶绿素a荧光、培养测定、活/死染色、共聚焦激光扫描显微镜（CLSM）和拉曼激光光谱（RLS）分析这些影响。结果表明光合作用受到剂量依赖性损伤、细胞增殖停止、细胞损伤、代谢活性降低以及光合色素降解。虽然先前对其他外星应激源的研究已证明具有很高的抗性潜力，但本研究结果揭示了共生光合生物对电离辐射抗性的极限，并描述了γ辐射诱导的损伤特征。本研究还支持了“STARLIFE”对圆卷地卷和优美黄藓（Xanthoria elegans）地衣的平行研究，这两种地衣都含有绿藻共生光合生物。关键词：天体生物学 - γ射线 - 极端耐受性 - 电离辐射 - 地衣 - 共生光合生物。《天体生物学》第17卷，第154 - 162页
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