The Isotopic Composition of Iron: A Chemical Fingerprint forBiologic Activity

铁的同位素组成：生物活性的化学指纹

• 批准号: 9713968
• 负责人: Brian Beard
• 金额: $ 6.3万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-01 至 2000-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9713968&HistoricalAwards=false
• 关键词: Isotopic; Composition; Iron; Chemical; Fingerprint

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.

摘要该奖项支持了一个项目，该项目旨在开发一种化学方法，利用铁（Fe）的同位素组成来识别陨石中的生物活性。它由极地项目办公室、化学部门和MPS多学科活动办公室提供支持。生物化学指纹图谱的发展将有助于：1)评估最近的解释，即ALH84001陨石包含火星上古代生物活动的证据，部分形式是超细粒度的磁铁矿和硫化物铁矿，据推测是由铁还原细菌形成的；2)筛选有生物活性的地外物质（陨石或从未来的其他行星任务中返回的样本）；3)确定地球上最早生命出现的时间限制。生物产生的含铁矿物无处不在，许多含铁生物矿物是由细菌产生的，它们将三铁还原为亚铁，从而形成氧化铁、硫化物或碳酸盐。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。细菌对硫酸盐的还原可以产生硫-34比硫-32的大分馏物。与硫酸盐还原细菌类似，根据铁和S同位素的相对质量分布，铁还原细菌预计能够产生与硫酸盐还原细菌所观察到的铁同位素分馏相同的分馏。Dixon等人对铁同位素的初步研究表明了这种程度的分馏，他们解释了他们在陆地样品中测量到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通过分析各种物理环境中无机生产的含铁矿物，为无机铁的同位素组成建立一个基线。评估由生物过程产生的铁同位素分馏将通过分析在受控的实验室环境中从分离的细菌菌株中生长出来的铁生物矿物来进行。有了这些限制，就有可能利用铁的同位素组成来评估火星陨石ALH84001中推断的铁生物矿物是无机产生的还是通过生物活动产生的。