Baqué Mickael, Verseux Cyprien, Böttger Ute, Rabbow Elke, de Vera Jean-Pierre Paul, Billi Daniela
Department of Biology, University of Rome Tor Vergata, Rome, Italy.
German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany.
Orig Life Evol Biosph. 2016 Jun;46(2-3):289-310. doi: 10.1007/s11084-015-9467-9. Epub 2015 Nov 3.
The space mission EXPOSE-R2 launched on the 24th of July 2014 to the International Space Station is carrying the BIOMEX (BIOlogy and Mars EXperiment) experiment aimed at investigating the endurance of extremophiles and stability of biomolecules under space and Mars-like conditions. In order to prepare the analyses of the returned samples, ground-based simulations were carried out in Planetary and Space Simulation facilities. During the ground-based simulations, Chroococcidiopsis cells mixed with two Martian mineral analogues (phyllosilicatic and sulfatic Mars regolith simulants) were exposed to a Martian simulated atmosphere combined or not with UV irradiation corresponding to the dose received during a 1-year-exposure in low Earth orbit (or half a Martian year on Mars). Cell survival and preservation of potential biomarkers such as photosynthetic and photoprotective pigments or DNA were assessed by colony forming ability assays, confocal laser scanning microscopy, Raman spectroscopy and PCR-based assays. DNA and photoprotective pigments (carotenoids) were detectable after simulations of the space mission (570 MJ/m(2) of UV 200-400 nm irradiation and Martian simulated atmosphere), even though signals were attenuated by the treatment. The fluorescence signal from photosynthetic pigments was differently preserved after UV irradiation, depending on the thickness of the samples. UV irradiation caused a high background fluorescence of the Martian mineral analogues, as revealed by Raman spectroscopy. Further investigation will be needed to ensure unambiguous identification and operations of future Mars missions. However, a 3-month exposure to a Martian simulated atmosphere showed no significant damaging effect on the tested cyanobacterial biosignatures, pointing out the relevance of the latter for future investigations after the EXPOSE-R2 mission. Data gathered during the ground-based simulations will contribute to interpret results from space experiments and guide our search for life on Mars.
2014年7月24日发射至国际空间站的“EXPOSE-R2”太空任务搭载了“BIOMEX”（生物学与火星实验）实验，旨在研究极端微生物在太空和类火星条件下的耐受性以及生物分子的稳定性。为了准备对返回样本的分析，在行星与太空模拟设施中进行了地面模拟。在地面模拟过程中，将与两种火星矿物类似物（层状硅酸盐和硫酸盐火星风化层模拟物）混合的嗜球藻属细胞暴露于模拟火星大气中，该大气可与对应低地球轨道1年暴露（或火星上半个火星年）期间所接收剂量的紫外线辐射相结合或不结合。通过菌落形成能力测定、共聚焦激光扫描显微镜、拉曼光谱和基于聚合酶链反应的测定来评估细胞存活情况以及光合色素、光保护色素或DNA等潜在生物标志物的保存情况。在模拟太空任务（200 - 400纳米紫外线辐射570兆焦耳/平方米以及模拟火星大气）之后，DNA和光保护色素（类胡萝卜素）仍可检测到，尽管信号因处理而减弱。光合色素的荧光信号在紫外线照射后根据样本厚度的不同而有不同程度的保存。拉曼光谱显示，紫外线照射导致火星矿物类似物产生高背景荧光。需要进一步研究以确保未来火星任务的明确识别和操作。然而，为期3个月的模拟火星大气暴露对所测试的蓝藻生物标志物未显示出显著的破坏作用，这表明其对于“EXPOSE-R2”任务之后的未来研究具有重要意义。在地面模拟过程中收集的数据将有助于解释太空实验的结果，并指导我们在火星上寻找生命。
