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The curious consistency of carbon biosignatures over billions of years of Earth-life coevolution
The ISME Journal ( IF 11.0 ) Pub Date : 2021-04-12 , DOI: 10.1038/s41396-021-00971-5
Amanda K Garcia 1 , Colleen M Cavanaugh 2 , Betul Kacar 1, 3
Affiliation  

The oldest and most wide-ranging signal of biological activity (biosignature) on our planet is the carbon isotope composition of organic materials preserved in rocks. These biosignatures preserve the long-term evolution of the microorganism-hosted metabolic machinery responsible for producing deviations in the isotopic compositions of inorganic and organic carbon. Despite billions of years of ecosystem turnover, evolutionary innovation, organismic complexification, and geological events, the organic carbon that is a residuum of the global marine biosphere in the rock record tells an essentially static story. The ~25‰ mean deviation between inorganic and organic 13C/12C values has remained remarkably unchanged over >3.5 billion years. The bulk of this record is conventionally attributed to early-evolved, RuBisCO-mediated CO2 fixation that, in extant oxygenic phototrophs, produces comparable isotopic effects and dominates modern primary production. However, billions of years of environmental transition, for example, in the progressive oxygenation of the Earth’s atmosphere, would be expected to have accompanied shifts in the predominant RuBisCO forms as well as enzyme-level adaptive responses in RuBisCO CO2-specificity. These factors would also be expected to result in preserved isotopic signatures deviating from those produced by extant RuBisCO in oxygenic phototrophs. Why does the bulk carbon isotope record not reflect these expected environmental transitions and evolutionary innovations? Here, we discuss this apparent discrepancy and highlight the need for greater quantitative understanding of carbon isotope fractionation behavior in extant metabolic pathways. We propose novel, laboratory-based approaches to reconstructing ancestral states of carbon metabolisms and associated enzymes that can constrain isotopic biosignature production in ancient biological systems. Together, these strategies are crucial for integrating the complementary toolsets of biological and geological sciences and for interpretation of the oldest record of life on Earth.



中文翻译:

数十亿年地球生命共同进化过程中碳生物特征的奇怪一致性

我们星球上最古老和最广泛的生物活动信号(生物特征)是保存在岩石中的有机材料的碳同位素组成。这些生物印记保留了微生物宿主代谢机制的长期演变,这些机制负责产生无机和有机碳同位素组成的偏差。尽管数十亿年的生态系统更替、进化创新、有机体复杂化和地质事件,岩石记录中作为全球海洋生物圈残留物的有机碳讲述了一个基本静止的故事。无机和有机13 C/ 12之间的平均偏差约为 25‰在超过 35 亿年的时间里,C 值保持显着不变。这一记录的大部分通常归因于早期进化的、RuBisCO 介导的 CO 2固定,在现存的含氧光养生物中,产生类似的同位素效应并主导现代初级生产。然而,数十亿年的环境转变,例如,在地球大气的逐渐氧化过程中,预计会伴随主要 RuBisCO 形式的变化以及 RuBisCO CO 2中酶水平的适应性反应-特异性。预计这些因素也会导致保留的同位素特征与含氧光养生物中现存的 RuBisCO 产生的同位素特征不同。为什么大量碳同位素记录不能反映这些预期的环境转变和进化创新?在这里,我们讨论了这种明显的差异,并强调需要对现存代谢途径中的碳同位素分馏行为进行更多的定量理解。我们提出了新的、基于实验室的方法来重建碳代谢和相关酶的祖先状态,这些方法可以限制古代生物系统中同位素生物印记的产生。总之,这些策略对于整合生物和地质科学的互补工具集以及解释地球上最古老的生命记录至关重要。

更新日期:2021-04-12
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