Biological nitrogen cycling within terrestrial hot springs: A Mars analogue system

IF 4.8 1区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Toni Galloway , Claire R. Cousins , Eva E. Stüeken , Jon Telling , Joanne S. Boden , Christopher E. Stead , Carla Greco , Arola Moreras-Martí , Mark G. Fox-Powell , Sophie L. Nixon
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Abstract

Noachian-age (4.1–3.7Ga) hot spring deposits have been identified on Mars, in addition to fixed nitrogen compounds within Martian surface materials, yet the planet’s nitrogen cycle remains enigmatic and implicates the plausibility of a Martian biosphere. On Earth’s surface, nitrogen is cycled almost exclusively by biological processes which create distinctive isotopic fractionations. We combine geochemical and metagenomic analysis to investigate biological nitrogen cycling within four Mars analogue geothermal systems in Iceland ranging in temperature from 37.8 to 57.1 °C, and propose the geochemical parameters that control biological nitrogen fixation as the primary source of nitrogen into the microbial communities present. We find complete nitrogen fixation and ammonium assimilation gene clusters at all sites, which are also the most abundant nitrogen-cycling genes present. Isotopic fractionations (Δ15 N) of ∼6 ‰ between locally dissolved N2 gas and biomass are most parsimoniously explained by organisms relying on Mo-independent nitrogenases for fixation of dinitrogen (N2). This hypothesis is supported by the presence of genes encoding these enzymes in three out of four sites included in this study, in addition to the more commonly used MoFe nitrogenase. Finally, we find that molybdenum availability is low in the Icelandic hot springs investigated, and potentially therefore in Martian hot springs. This may inhibit conventional Mo-dependent nitrogen fixation in such settings and highlights the influence of wider geological conditions on local biochemistry.
陆地温泉中的生物氮循环:火星模拟系统
诺亚时代(4.1-3.7Ga)的温泉沉积物已经在火星上被发现,除了火星表面物质中的固定氮化合物外,火星的氮循环仍然是一个谜,这暗示了火星生物圈的可能性。在地球表面,氮几乎完全通过生物过程循环,从而产生独特的同位素分馏。我们将地球化学和元基因组分析相结合,研究了冰岛四个温度范围为37.8 ~ 57.1°C的火星模拟地热系统中的生物氮循环,并提出了控制生物固氮作为氮主要来源进入微生物群落的地球化学参数。我们在所有位点上发现完整的固氮和铵同化基因簇,这也是最丰富的氮循环基因。局部溶解的N2气体和生物质之间的同位素分异(Δ15 N)为~ 6‰,最简单的解释是生物体依赖于不依赖于mo的固氮酶来固定二氮(N2)。除了更常用的MoFe氮酶外,在本研究中包含的四个位点中有三个位点存在编码这些酶的基因,这一假设得到了支持。最后,我们发现钼在冰岛温泉中的可用性很低,因此可能在火星温泉中也是如此。这可能会抑制这种环境下传统的依赖于钼的固氮作用,并突出了更广泛的地质条件对当地生物化学的影响。
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来源期刊
Earth and Planetary Science Letters
Earth and Planetary Science Letters 地学-地球化学与地球物理
CiteScore
10.30
自引率
5.70%
发文量
475
审稿时长
2.8 months
期刊介绍: Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.
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