Gypsum (CaSO4·2H2O) has been identified at the surface of Mars, by both orbiters and rovers. Because gypsum mostly forms in the presence of liquid water as an essential element for sustaining microbial life and has a low porosity, which is ideal for preserving organic material, it is a promising target to look for signs of past microbial life. In this article, we studied organic matter preservation within gypsum that precipitates in a salt flat or a so-called coastal sabkha located in Qatar. Sabkha's ecosystem is considered a modern analog to evaporitic environments that may have existed on early Mars. We collected the sediment cores in the areas where gypsum is formed and performed DNA analysis to characterize the community of extremophilic microorganisms that is present at the site of gypsum formation. Subsequently, we applied Raman spectroscopy, a technique available on several rovers that are currently exploring Mars, to evaluate which organic molecules can be detected through the translucent gypsum crystals. We showed that organic material can be encapsulated into evaporitic gypsum and detected via Raman microscopy with simple, straightforward sample preparation. The molecular biology data proved useful for assessing to what extent complex Raman spectra can be linked to the original microbial community, dominated by Halobacteria and methanogenic archaea, providing a reference for a signal that may be detected on Mars.

中文翻译：

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高盐湿地石膏沉积物生物膜的拉曼光谱和微生物研究：天体生物学视角。

轨道飞行器和漫游车均在火星表面发现了石膏 (CaSO4·2H2O)。由于石膏主要是在液态水的存在下形成的，液态水是维持微生物生命的基本元素，并且具有较低的孔隙率，这是保存有机材料的理想选择，因此它是寻找过去微生物生命迹象的一个有希望的目标。在本文中，我们研究了在卡塔尔盐滩或所谓的沿海萨布哈沉淀的石膏中有机物的保存。萨布哈的生态系统被认为是早期火星上可能存在的蒸发环境的现代模拟。我们收集了石膏形成区域的沉积物岩心，并进行了 DNA 分析，以表征石膏形成地点存在的极端微生物群落。随后，我们应用拉曼光谱（目前正在探索火星的几辆漫游车上可用的技术）来评估可以通过半透明石膏晶体检测到哪些有机分子。我们证明，有机材料可以封装到蒸发石膏中，并通过拉曼显微镜通过简单、直接的样品制备进行检测。分子生物学数据被证明有助于评估复杂的拉曼光谱在多大程度上可以与以盐细菌和产甲烷古菌为主的原始微生物群落联系起来，为可能在火星上检测到的信号提供参考。