Oren Aharon
Department of Plant and Environmental Sciences, The Alexander Silverman Institute of Life Sciences, The Edmond J. Safra Campus, Givat Ram, Jerusalem 91904, Israel
Philos Trans A Math Phys Eng Sci. 2014 Dec 13;372(2030). doi: 10.1098/rsta.2014.0194.
Salts are abundant on Mars, and any liquid water that is present or may have been present on the planet is expected to be hypersaline. Halophilic archaea (family Halobacteriaceae) are the microorganisms best adapted to life at extremes of salinity on Earth. This paper reviews the properties of the Halobacteriaceae that may make the group good candidates for life also on Mars. Many species resist high UV and gamma radiation levels; one species has survived exposure to vacuum and radiation during a space flight; and there is at least one psychrotolerant species. Halophilic archaea may survive for millions of years within brine inclusions in salt crystals. Many species have different modes of anaerobic metabolism, and some can use light as an energy source using the light-driven proton pump bacteriorhodopsin. They are also highly tolerant to perchlorate, recently shown to be present in Martian soils, and some species can even use perchlorate as an electron acceptor to support anaerobic growth. The presence of characteristic carotenoid pigments (α-bacterioruberin and derivatives) makes the Halobacteriaceae easy to identify by Raman spectroscopy. Thus, if present on Mars, such organisms may be detected by Raman instrumentation planned to explore Mars during the upcoming ExoMars mission.
火星上盐类丰富，该行星上现存或可能曾经存在的任何液态水预计都是高盐度的。嗜盐古菌（嗜盐杆菌科）是地球上最适应在极端盐度环境下生存的微生物。本文综述了嗜盐杆菌科的特性，这些特性可能使该类群也成为火星生命的理想候选者。许多物种能抵抗高紫外线和伽马辐射水平；有一个物种在太空飞行中经受住了真空和辐射的考验；并且至少有一个耐冷物种。嗜盐古菌可以在盐晶体中的盐水包裹体内存活数百万年。许多物种有不同的厌氧代谢模式，有些可以利用光驱动的质子泵细菌视紫红质将光作为能量来源。它们对高氯酸盐也具有高度耐受性，最近发现火星土壤中存在高氯酸盐，有些物种甚至可以利用高氯酸盐作为电子受体来支持厌氧生长。特征性类胡萝卜素色素（α-细菌红素及其衍生物）的存在使得通过拉曼光谱法很容易识别嗜盐杆菌科。因此，如果火星上存在此类生物，那么在即将到来的“火星外生物学”任务中计划用于探索火星的拉曼仪器可能会检测到它们。
