1 Department of Chemistry and Biochemistry, George Mason University , Fairfax, Virginia, USA.
2 School of Earth and Space Exploration, Arizona State University , Tempe, Arizona, USA.
Astrobiology. 2018 Jan;18(1):73-85. doi: 10.1089/ast.2016.1510. Epub 2018 Jan 9.
Life on Earth is found in a wide range of environments as long as the basic requirements of a liquid solvent, a nutrient source, and free energy are met. Previous hypotheses have speculated how extraterrestrial microbial life may function, among them that particle radiation might power living cells indirectly through radiolytic products. On Earth, so-called electrophilic organisms can harness electron flow from an extracellular cathode to build biomolecules. Here, we describe two hypothetical mechanisms, termed "direct electrophy" and "indirect electrophy" or "fluorosynthesis," by which organisms could harness extracellular free electrons to synthesize organic matter, thus expanding the ensemble of potential habitats in which extraterrestrial organisms might be found in the Solar System and beyond. The first mechanism involves the direct flow of secondary electrons from particle radiation to a microbial cell to power the organism. The second involves the indirect utilization of impinging secondary electrons and a fluorescing molecule, either biotic or abiotic in origin, to drive photosynthesis. Both mechanisms involve the attenuation of an incoming particle's energy to create low-energy secondary electrons. The validity of the hypotheses is assessed through simple calculations showing the biomass density attainable from the energy supplied. Also discussed are potential survival strategies that could be used by organisms living in possible habitats with a plentiful supply of secondary electrons, such as near the surface of an icy moon. While we acknowledge that the only definitive test for the hypothesis is to collect specimens, we also describe experiments or terrestrial observations that could support or nullify the hypotheses. Key Words: Radiation-Electrophiles-Subsurface life. Astrobiology 18, 73-85.
只要满足液体溶剂、营养源和自由能这三个基本要求，地球上的生命就可以在广泛的环境中存在。先前的假设推测了外星微生物生命可能的运作方式，其中包括认为粒子辐射可能通过辐射分解产物间接为活细胞提供动力。在地球上，所谓的亲电生物可以利用来自细胞外阴极的电子流来构建生物分子。在这里，我们描述了两种假设机制，分别称为“直接亲电性”和“间接亲电性”或“氟合成”，通过这些机制，生物体可以利用细胞外的自由电子来合成有机物，从而扩大了太阳系内外可能存在外星生物的潜在栖息地范围。第一种机制涉及从粒子辐射到微生物细胞的二次电子的直接流动，为生物体提供动力。第二种机制涉及撞击二次电子和荧光分子的间接利用，这些分子可以是生物起源的，也可以是无生命起源的，从而驱动光合作用。这两种机制都涉及到入射粒子能量的衰减，以产生低能二次电子。通过显示从提供的能量中获得的生物量密度的简单计算来评估假设的有效性。还讨论了可能在大量二次电子存在的潜在栖息地中生存的生物体可以使用的潜在生存策略，例如在冰冷卫星的表面附近。虽然我们承认该假设的唯一明确测试是收集标本，但我们也描述了可能支持或否定该假设的实验或地球观测。关键词：辐射-亲电体-地下生命。天体生物学 18,73-85。
