Brandt Annette, Posthoff Eva, de Vera Jean-Pierre, Onofri Silvano, Ott Sieglinde
Institute of Botany, Heinrich-Heine-University (HHU), Universitaetsstr. 1, 40225, Duesseldorf, Germany.
Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstr. 2, 12489, Berlin, Germany.
Orig Life Evol Biosph. 2016 Jun;46(2-3):311-21. doi: 10.1007/s11084-015-9470-1. Epub 2015 Nov 2.
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.
地衣华丽黄藻在国际空间站（ISS）的EXPOSE - E设施上的地衣与真菌实验（LIFE）中，被暴露于太空和模拟火星的环境中。这次长达559天的长期暴露测试了各种生物体应对低地球轨道（LEO）或火星模拟条件的能力，如真空、火星模拟大气、快速温度循环、高达215±16 mGy的宇宙辐射以及累积剂量高达4.87 GJm(-2)的日照，包括高达0.314 GJm(-2)的紫外线照射。在先前的一项研究中，华丽黄藻通过光合活性以及暴露后藻类共生体50 - 80%和真菌共生体60 - 90%的代谢活性，表现出对这些条件相当的抗性（布兰特等人，《国际天体生物学杂志》14(3):411 - 425，2015）。本研究的两个目标是相辅相成的：第一，通过定性培养试验验证暴露后的高活力。第二，通过透射电子显微镜（TEM）表征由LIFE的太空和火星模拟暴露条件引起的细胞损伤。由于地衣的藻类共生体被认为是更易受影响的伙伴（德维拉和奥特，2010），分析集中在光合生物上。该研究表明，在LIFE的所有暴露条件下，分离出的光合生物都能生长和增殖。藻类细胞的超微结构分析揭示了长期暴露引起的细胞损伤，并突出表明，在更严酷的太空真空中，干燥诱导的细胞完整性破坏比在火星模拟大气条件下更为明显。总之，干燥诱导的损伤被确定为华丽黄藻光合生物的主要威胁。尽管如此，在LIFE测试的所有暴露条件下，仍有一部分光合生物细胞可培养。
