图为生长在智利阿塔卡马沙漠地下两米疏水基底的微生物
近日，美国物理学家组织网报道，西班牙天体生物学中心和智利北部天主教大学的研究人员，通过一种类似于探测火星土壤底层生命迹象的仪器，在智利阿塔卡马沙漠地下两米的疏水基底发现一个“微生物的绿洲”。这个有关“生命能够在地球上最干旱的沙漠下繁衍”的研究刊登在最新一期的《天体生物学》Astrobiology杂志上。
该团队的科学家在这个沙漠下的“绿洲”发现了栖息的细菌和古生菌（原始微生物），于是将其命名为“微生物的绿洲”。西班牙天体生物学中心研究员维克托解释说，微生物得以栖息是因为这里蕴含可吸附水分的岩盐和其他高吸湿化合物，如硬石膏和高氯酸盐。此外，基底下的微生物易潮解，这意味着它们可以吸收有限空气中的水分，凝结于盐晶体表面，从而形成了几微米厚的薄膜。这些物种与其他类似的在多盐环境下生长的种类没有什么不同，只是奇特的是，它们竟被发现在没有任何氧气或阳光的地下2米至3米深处。
在这项科学研究中，该小组采用的是自行开发被称为SOLID的探测仪探测生命迹象，以备未来用于火星探测任务。该仪器的核心是一种叫作LD Chip的生物芯片，包括450种抗体，以确定生物材料，如糖、DNA和蛋白质。其可将采集的样本自动进行培养和处理，用影像来反映观察结果，如果其中有亮点即表明其中存在某些化合物和微生物。
研究人员通过这种技术证实在沙漠底下有古生菌和细菌的存在。他们把沙漠深度达5米处所采集的样品带进实验室，不仅用电子显微镜观察拍照，还为这些微生物补给水分。
维克托强调，如果火星上有类似的微生物或其上有相似的环境，也可以采用在阿塔卡马沙漠的这种仪器来探测。在这个红色星球上已发现含盐水的沉积物，因此其底土有可能存在多盐的环境。而这种高浓度的盐具有双重作用，既可吸收晶体的水，又可降低冰点，使其能够在零下几摄氏度到20摄氏度形成薄盐膜。（生物谷Bioon.com）
doi:10.1089/ast.2011.0654
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A Microbial Oasis in the Hypersaline Atacama Subsurface Discovered by a Life Detector Chip: Implications for the Search for Life on Mars
Victor Parro,1 Graciela de Diego-Castilla,1 Mercedes Moreno-Paz,1 Yolanda Blanco,1 Patricia Cruz-Gil,1 José A. Rodríguez-Manfredi,2 David Fernández-Remolar,3 Felipe Gómez,3 Manuel J. Gómez,1 Luis A. Rivas,1 Cecilia Demergasso,4,5 Alex Echeverría,4 Viviana N. Urtuvia,4 Marta Ruiz-Bermejo,1 Miriam García-Villadangos,1 Marina Postigo,1 Mónica Sánchez-Román,3 Guillermo Chong-Díaz,5,6 and Javier Gómez-Elvira2
The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5 m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2 m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5 g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260 g kg−1) and perchlorate (41.13 μg g−1 maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14 μg g−1) or formate (76.06 μg g−1) as electron donors, and sulfate (15875 μg g−1), nitrate (13490 μg g−1), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars.
