Cortesão Marta, Fuchs Felix M, Commichau Fabian M, Eichenberger Patrick, Schuerger Andrew C, Nicholson Wayne L, Setlow Peter, Moeller Ralf
Space Microbiology Research Group, Radiation Biology Department, Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany.
Department of General Microbiology, Institute for Microbiology and Genetics, University of Göttingen, Göttingen, Germany.
Front Microbiol. 2019 Feb 26;10:333. doi: 10.3389/fmicb.2019.00333. eCollection 2019.
In a Mars exploration scenario, knowing if and how highly resistant spores would survive on the Martian surface is crucial to design planetary protection measures and avoid false positives in life-detection experiments. Therefore, in this study a systematic screening was performed to determine whether spores could survive an average day on Mars. For that, spores from two comprehensive sets of isogenic mutant strains, defective in DNA protection or repair genes, were exposed to 24 h of simulated Martian atmospheric environment with or without 8 h of Martian UV radiation [M(+)UV and M(-)UV, respectively]. When exposed to M(+)UV, spore survival was dependent on: (1) core dehydration maintenance, (2) protection of DNA by α/β-type small acid soluble proteins (SASP), and (3) removal and repair of the major UV photoproduct (SP) in spore DNA. In turn, when exposed to M(-)UV, spore survival was mainly dependent on protection by the multilayered spore coat, and DNA double-strand breaks represent the main lesion accumulated. spores were able to survive for at least a limited time in a simulated Martian environment, both with or without solar UV radiation. Moreover, M(-)UV-treated spores exhibited survival rates significantly higher than the M(+)UV-treated spores. This suggests that on a real Martian surface, radiation shielding of spores (e.g., by dust, rocks, or spacecraft surface irregularities) might significantly extend survival rates. Mutagenesis were strongly dependent on the functionality of all structural components with small acid-soluble spore proteins, coat layers and dipicolinic acid as key protectants and efficiency DNA damage removal by AP endonucleases (ExoA and Nfo), non-homologous end joining (NHEJ), mismatch repair (MMR) and error-prone translesion synthesis (TLS). Thus, future efforts should focus on: (1) determining the DNA damage in wild-type spores exposed to M(+/-)UV and (2) assessing spore survival and viability with shielding of spores via Mars regolith and other relevant materials.
在火星探索的设想中，了解具有高度抗性的孢子是否以及如何在火星表面存活，对于设计行星保护措施以及避免生命探测实验中的误报至关重要。因此，在本研究中进行了系统筛选，以确定孢子能否在火星上度过平均一天的时间。为此，从两组全面的同基因突变菌株中获取孢子，这些菌株在DNA保护或修复基因方面存在缺陷，将其暴露于模拟火星大气环境24小时，有或没有8小时的火星紫外线辐射[分别为M(+)UV和M(-)UV]。当暴露于M(+)UV时，孢子存活取决于：(1)核心脱水维持，(2)α/β型小酸溶性蛋白(SASP)对DNA的保护，以及(3)孢子DNA中主要紫外线光产物(SP)的去除和修复。反过来，当暴露于M(-)UV时，孢子存活主要取决于多层孢子壁的保护，并且DNA双链断裂是积累的主要损伤。孢子在模拟火星环境中，无论有无太阳紫外线辐射，都能够存活至少一段有限的时间。此外，经M(-)UV处理的孢子的存活率显著高于经M(+)UV处理的孢子。这表明在真实的火星表面，孢子的辐射屏蔽（例如，通过尘埃、岩石或航天器表面不规则处）可能会显著延长存活率。诱变强烈依赖于所有结构成分的功能，其中小酸溶性孢子蛋白、壁层和吡啶二羧酸作为关键保护剂，以及由AP核酸内切酶（ExoA和Nfo）、非同源末端连接(NHEJ)、错配修复(MMR)和易错跨损伤合成(TLS)对DNA损伤的有效去除。因此，未来的工作应集中在：(1)确定暴露于M(+/-)UV的野生型孢子中的DNA损伤，以及(2)通过火星风化层和其他相关材料对孢子进行屏蔽来评估孢子的存活和活力。
