The Isotopic Composition of Iron: A Chemical Fingerprint forBiologic Activity

9713968比尔德，约翰逊 摘要 该奖项支持一个项目，开发一种化学方法，使用铁（Fe）的同位素组成来识别陨石中的生物活性。 它由极地计划办公室，化学部和MPS多学科活动办公室支持。 开发生物化学指纹将有助于： 1)评价最近的解释，即ALH 84001陨石含有火星上古代生物活动的证据，部分以超细粒磁铁矿和硫化物铁矿物的形式存在，推测这些矿物是由铁还原细菌形成的; 2)筛选地外物质的生物活性（陨石或从未来其他行星的飞行任务返回的样本）; 3)为地球上最早的生命设定了时限 生物产生的含铁矿物是普遍存在的，许多铁生物矿物是由细菌产生的，它们将三价铁还原为二价铁，从而形成铁氧化物、铁硫化物或铁碳酸盐。 铁还原的代谢途径与细菌将硫酸盐还原为硫化物的代谢途径相同。 硫酸盐的细菌还原可以产生硫-34与硫-32比率的大分馏。 与硫酸盐还原菌类似，铁还原菌预期能够产生Fe同位素分馏，其基于Fe和S同位素的相对质量扩散，与硫酸盐还原菌所观察到的那些Fe同位素分馏相当。 狄克逊等人对铁同位素的初步研究表明了这种分馏的程度，他们解释了他们在陆地样品中测量的铁同位素比率变化，以反映生物诱导的铁同位素分馏。 这项研究的范围将是建立一个基线的无机铁的同位素组成的无机铁的分析无机生产的含铁矿物从各种物理环境。 通过分析在受控实验室环境中从分离的细菌菌株中生长的铁生物矿物，评估生物过程产生的铁同位素分馏。 有了这些限制，它将有可能使用铁的同位素组成，以评估是否推断铁生物矿物在火星陨石ALH 84001产生无机或生物活动。

9713968 Beard, Johnson Abstract This award supports a project to develop a chemical method for fingerprinting biological activity in meteorites using the isotopic composition of iron (Fe). It is supported by the Office of Polar Programs, the Chemistry Division, and the MPS Office of Multidisciplinary Activities. Development of a biological chemical fingerprint will be useful in: 1) evaluating the recent interpretations that meteorite ALH84001 contains evidence of ancient biological activity on Mars, partly in the form of ultra-fine-grained magnetite and sulfide iron minerals that are inferred to have been formed by iron-reducing bacteria; 2) screening extraterrestrial material for biological activity (meteorites or samples returned from future missions to other planets); and 3) establishing the time limits for the earliest life on Earth. Biologically produced iron-bearing minerals are ubiquitous, and many iron biominerals are produced by bacteria that reduce ferric iron to ferrous iron, resulting in formation of iron-oxides, - sulfides, or -carbonates. The metabolic pathway for iron reduction is the same as that used by bacteria which reduce sulfate to sulfide. Bacteria reduction of sulfate can produce large fractionations in sulfur-34 to sulfur-32 ratios. By analogy to sulfate-reducing bacteria, iron reducing bacteria are expected to be capable of producing Fe isotope fractionations that are on the order of those observed for sulfate reducing bacteria, based on the relative mass spread of Fe and S isotopes. This magnitude of fractionation is suggested by preliminary studies of Fe isotopes by Dixon et al., who interpret the Fe isotope ratio variations they measured in terrestrial samples to reflect biologically-induced Fe isotope fractionation. The scope of this research will be to establish a baseline for the isotopic composition of inorganic iron by analysis of inorganically produced Fe-bearing minerals from a variety of physical settings . Evaluating the Fe isotope fractionation produced by biological processes will be conducted by analyzing iron biominerals that were grown from isolated bacteria strains in a controlled laboratory environment. With these limits established, it will be possible to use the isotopic composition of Fe to evaluate if inferred iron biominerals in Martian meteorite ALH84001 were produced inorganically or by biological activity.