There's Plenty of Room at the Bottom: Low Radiation as a Biological Extreme
There's Plenty of Room at the Bottom: Low Radiation as a Biological Extreme
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DOI：
10.3389/fspas.2020.00050
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
J. Wadsworth;C. Cockell;A. Murphy;A. Nilima;S. Paling;E. Meehan;C. Toth;P. Scovell;L. Cascorbi
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文献类型：
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作者：
J. Wadsworth;C. Cockell;A. Murphy;A. Nilima;S. Paling;E. Meehan;C. Toth;P. Scovell;L. Cascorbi
高辐射作为一种生物极端现象，其影响在辐射生物学和天体生物学领域历来并将继续得到广泛的研究。然而，科学界对缺乏辐射这一极端现象的关注相对有限，其对生命的影响尚不清楚。目前被接受的生物辐射剂量-损伤关系模型是线性无阈值(LNT)模型，该模型预测剂量与与零损害对应的零剂量截获的损害之间存在正向线性相关。尽管LNT模型的实施范围很广，但它仍不断受到各种新模型的挑战，其中Hormesis模型是其主要竞争对手之一。这个模型也假设了高剂量下的损伤，但与LNT模型不同，它预测了低剂量下有益的生长刺激。到目前为止，实验还没有能够最终验证或否定这两个模型中的任何一个。合作低辐射生命地下实验(SELLR)项目的目的是在一个特征良好的环境中在原核生物上测试这些相互竞争的模型，并提供一个强大的实验装置来研究陆地和非陆地环境中的低辐射。在Boulby矿的Boulby地下实验室(英国雷德卡和克利夫兰)的Boulby国际地下天体生物学实验室(BISAL)设施中，在超低电离辐射下进行了枯草芽孢杆菌和大肠杆菌的细菌生长测试，并用于研究对活性和预适应迹象的影响。从陆地表面环境中通常发现的本底辐射水平的0.01倍到本底辐射水平的100倍，暴露在辐射剂量下对细菌生长没有显著影响。此外，在生长在持续低辐射中的细菌菌株中，没有观察到对应激的预适应敏感性。这些数据表明，极端的低辐射不会改变这两种生物的生长参数，应该考虑对原核生物建立一个改进的模型，该模型包括在超低辐射下具有阈值的剂量-损伤响应。我们讨论了这些数据对低辐射作为一种新的微生物“极端”的影响。
The effects of high radiation as a biological extreme have historically been, and continue to be, extensively researched in the fields of radiation biology and astrobiology. However, the absence of radiation as an extreme has received relatively limited attention from the scientific community, with its effects on life remaining unclear. The currently accepted model of the radiation dose-damage relationship for organisms is the linear no-threshold (LNT) model, which predicts a positive linear correlation between dose and damage that intercepts at zero dose corresponding to zero damage. Despite its wide-spread implementation, the LNT model is continuously being challenged by various new models, with the hormesis model as one of its main competitors. This model also postulates damage at high doses but, in contrast to the LNT model, it predicts beneficial stimulation of growth at low doses. Experiments to date have not yet been able to conclusively validate or dismiss either of these models. The aim of the collaborative Subsurface Experiment of Life in Low Radiation (SELLR) project was to test these competing models on prokaryotes in a well-characterised environment and provide a robust experimental set up to investigate low radiation in terrestrial and non-terrestrial environments. Bacterial growth assays using Bacillus subtilis and Escherichia coli were performed under ultra low ionising radiation in the Boulby International Subsurface Astrobiology Laboratory (BISAL) facilities of the Boulby Underground Laboratory at Boulby mine (Redcar & Cleveland, UK) and were used to investigate effects on viability and signs of preconditioning. No significant effect on bacterial growth was observed from exposure to radiation doses ranging from 0.01 times the levels of background radiation typically found in terrestrial surface environments to 100 times that background. Additionally, no preconditioned susceptibility to stress was observed in the bacterial strains grown in sustained low radiation. These data suggest that the extremes of low radiation do not alter growth parameters of these two organisms and that an improved model should be considered for prokaryotes, consisting of a dose-damage response with a threshold at ultra low radiation. We discuss the implications of these data for low radiation as a novel microbiological “extreme.”