Limitations of microbial iron reduction under extreme conditions.
Limitations of microbial iron reduction under extreme conditions.
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DOI：
10.1093/femsre/fuac033
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发表时间：
2022-11-02
影响因子：
11.3
通讯作者：
Cockell, Charles S.
中科院分区：
文献类型：
--
作者：
Nixon, Sophie L.;Bonsall, Emily;Cockell, Charles S.
微生物铁还原是地球上一种广泛存在且古老的代谢方式，并且可能合理地支持火星及其他星球上的微生物生命。然而，这种代谢的极限尚未确定。为了研究这一问题，我们调查了大量已鉴定的铁还原微生物（n = 141）中铁还原的记录极限，重点关注pH值和温度。然后，我们计算了在pH - 温度可居住空间内常见的微生物介导的铁还原反应的吉布斯自由能，以确定热力学极限。通过比较预测极限和观察到的极限，我们发现微生物铁还原通常仅在极端的pH值或温度下被报道，而当这些极端情况同时存在时则未被报道（少数嗜酸嗜热菌除外）。这些模式使得pH值和温度在热力学上有利的组合显然未被占据。这些空白区域可能是由实验偏差造成的，但也可能是由综合极端条件下铁还原的能量和生化限制所导致的。我们的数据有助于回顾我们目前对微生物在极端条件下铁还原极限的理解，并为检验关于生物化学在多大程度上确定生命极限的更一般性假设提供了基础。
作者对迄今为止已鉴定的铁还原微生物所观察到的生长极限进行了全面综述，同时利用热力学计算对能量极限进行了预测，并讨论了这种广泛存在且古老的代谢方式在可居住空间中尚未探索的区域，这对我们理解地球上最极端环境中的生命以及在其他地方寻找生命具有重要意义。
Microbial iron reduction is a widespread and ancient metabolism on Earth, and may plausibly support microbial life on Mars and beyond. Yet, the extreme limits of this metabolism are yet to be defined. To investigate this, we surveyed the recorded limits to microbial iron reduction in a wide range of characterized iron-reducing microorganisms (n = 141), with a focus on pH and temperature. We then calculated Gibbs free energy of common microbially mediated iron reduction reactions across the pH–temperature habitability space to identify thermodynamic limits. Comparing predicted and observed limits, we show that microbial iron reduction is generally reported at extremes of pH or temperature alone, but not when these extremes are combined (with the exception of a small number of acidophilic hyperthermophiles). These patterns leave thermodynamically favourable combinations of pH and temperature apparently unoccupied. The empty spaces could be explained by experimental bias, but they could also be explained by energetic and biochemical limits to iron reduction at combined extremes. Our data allow for a review of our current understanding of the limits to microbial iron reduction at extremes and provide a basis to test more general hypotheses about the extent to which biochemistry establishes the limits to life. The authors present a comprehensive review of the observed limits of growth by iron-reducing microorganisms characterized to date, alongside predictions of energetic limits using thermodynamic calculations, and discuss the unexplored regions of the habitability space for this widespread and ancient metabolism, with implications for our understanding of life in the most extreme environments on Earth and the search for life elsewhere.
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影响因子：
5
作者：
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