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Radiation of nitrogen‐metabolizing enzymes across the tree of life tracks environmental transitions in Earth history
Geobiology ( IF 3.7 ) Pub Date : 2020-10-27 , DOI: 10.1111/gbi.12419
Chris Parsons 1, 2 , Eva E Stüeken 3 , Caleb J Rosen 1 , Katherine Mateos 1 , Rika E Anderson 1, 4
Affiliation  

Nitrogen is an essential element to life and exerts a strong control on global biological productivity. The rise and spread of nitrogen‐utilizing microbial metabolisms profoundly shaped the biosphere on the early Earth. Here, we reconciled gene and species trees to identify birth and horizontal gene transfer events for key nitrogen‐cycling genes, dated with a time‐calibrated tree of life, in order to examine the timing of the proliferation of these metabolisms across the tree of life. Our results provide new insights into the evolution of the early nitrogen cycle that expand on geochemical reconstructions. We observed widespread horizontal gene transfer of molybdenum‐based nitrogenase back to the Archean, minor horizontal transfer of genes for nitrate reduction in the Archean, and an increase in the proliferation of genes metabolizing nitrite around the time of the Mesoproterozoic (~1.5 Ga). The latter coincides with recent geochemical evidence for a mid‐Proterozoic rise in oxygen levels. Geochemical evidence of biological nitrate utilization in the Archean and early Proterozoic may reflect at least some contribution of dissimilatory nitrate reduction to ammonium (DNRA) rather than pure denitrification to N2. Our results thus help unravel the relative dominance of two metabolic pathways that are not distinguishable with current geochemical tools. Overall, our findings thus provide novel constraints for understanding the evolution of the nitrogen cycle over time and provide insights into the bioavailability of various nitrogen sources in the early Earth with possible implications for the emergence of eukaryotic life.

中文翻译:

生命树中氮代谢酶的辐射追踪地球历史上的环境转变

氮是生命的基本元素,对全球生物生产力有很强的控制作用。利用氮的微生物代谢的兴起和传播深刻地塑造了早期地球的生物圈。在这里,我们协调了基因和物种树,以确定关键氮循环基因的出生和水平基因转移事件,日期与时间校准的生命树有关,以检查这些新陈代谢在生命树中增殖的时间. 我们的结果为扩展地球化学重建的早期氮循环的演变提供了新的见解。我们观察到钼基固氮酶的广泛水平基因转移回太古代,太古宙中硝酸盐还原基因的少量水平转移,并且在中元古代(~1.5 Ga)前后代谢亚硝酸盐的基因增殖增加。后者与最近的地球化学证据相吻合,即中元古代氧气水平升高。太古宙和元古代早期生物硝酸盐利用的地球化学证据可能至少反映了硝酸盐异化还原成铵(DNRA)而不是纯反硝化对N的贡献2 . 因此,我们的结果有助于揭示两种代谢途径的相对优势,这两种代谢途径无法与当前的地球化学工具区分开来。总体而言,我们的研究结果为理解氮循环随时间的演变提供了新的限制,并为了解早期地球中各种氮源的生物利用度提供了见解,这可能对真核生命的出现产生影响。
更新日期:2020-10-27
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