類火星環境中脂質生物特徵的命運

論文標題：The Fate of Lipid Biosignatures in a Mars-Analogue Sulfur Stream

作者：Jonathan Tan, James M. T. Lewis & Mark A. Sephton

數字識別碼：10.1038/s41598-018-25752-7

《科學報告》發表的一項研究The Fate of Lipid Biosignatures in a Mars-Analogue Sulfur Stream探究了在類比火星環境的酸性流中嗜酸生物的有機反應。

在火星上生存過的生物會產生有機殘留物，這些殘留物可能被保存在火星岩石中。在火星歷史上保留有大面積地表水的最近的一個時期是在晚諾亞紀和早赫斯伯利亞紀之間，水的存在使得火星在這段時期可以維持進化程度較高且分布廣泛的火星生命。通過對地球上類酸性和高硫環境的研究，可以為探究晚諾亞紀和早赫斯伯利亞紀時期的岩石提供指導。來自英國帝國理工學院的James M. T. Lewis及其同事，報道了在含有嗜酸生物的酸性流中的有機反應，這些嗜酸生物死後的殘骸被埋在硫酸鐵和氧化鐵中。研究人員發現，如果赫斯伯利亞紀時期有生命存在，火星上有機物質的記錄將包括微生物脂質。脂質在火星上是一個潛在的且巨大的化石碳儲藏庫，可以用來區分不同領域的生命。脂質的濃度，尤其是鏈烷酸或脂肪酸，在針鐵礦層含量最高，這反映出岩石中較高的含水比例，因此具有較高的可居住性。在火星上，針鐵礦普遍可以脫水轉化為赤鐵礦。未來，火星探測的任務應該是在高硫環境下鐵的氧化物和氫氧化物中檢測脂肪酸或者其成岩產物。

摘要：Past life on Mars will have generated organic remains that may be preserved in present day Mars rocks. The most recent period in the history of Mars that retained widespread surface waters was the late Noachian and early Hesperian and thus possessed the potential to sustain the most evolved and widely distributed martian life. Guidance for investigating late Noachian and early Hesperian rocks is provided by studies of analogous acidic and sulfur-rich environments on Earth. Here we report organic responses for an acid stream containing acidophilic organisms whose post-mortem remains are entombed in iron sulphates and iron oxides. We find that, if life was present in the Hesperian, martian organic records will comprise microbial lipids. Lipids are a potential sizeable reservoir of fossil carbon on Mars, and can be used to distinguish between different domains of life. Concentrations of lipids, and particularly alkanoic or 「fatty」 acids, are highest in goethite layers that reflect high water-to-rock ratios and thus a greater potential for habitability. Goethite can dehydrate to hematite, which is widespread on Mars. Mars missions should seek to detect fatty acids or their diagenetic products in the oxides and hydroxides of iron associated with sulphur-rich environments.

期刊介紹：Scientific Reportsis an online, open access journal from the publishers of Nature. We publish scientifically valid primary research from all areas of the natural and clinical sciences.

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