Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA.
Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan.
Sci Rep. 2021 Jan 22;11(1):2070. doi: 10.1038/s41598-021-81718-2.
The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial reactions in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O, the timing of its evolution-especially as it relates to the Great Oxygenation Event ~ 2.3 billion years ago-remains contested and is pivotal to our understanding of nutrient cycles. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.
现代氮循环由一系列微生物介导的氧化还原转化组成。在这个循环中，最重要的反应之一是氨氧化为亚硝酸盐，这是一个严格需氧的过程，由少数细菌（AOB）和古菌（AOA）谱系完成。由于这个过程对氧气有绝对的需求，其进化的时间——特别是它与 23 亿年前的大氧化事件的关系——仍然存在争议，这对我们理解营养循环至关重要。为了估计细菌氨氧化的古老程度，我们对 AOB 进行了系统发育和分子钟分析。令人惊讶的是，细菌氨氧化似乎相当年轻，冠群分支起源于新元古代（或更晚），主要辐射发生在古生代。这些结果表明，AOB 的进化与深海的普遍氧化大致同时发生。AOB 的晚期进化挑战了早期对古氮同位素记录的解释，预测了 AOA 在寒武纪时期将发挥更重要的作用，并且可能对理解地质历史时期生物地球化学氮循环的规模和结构具有重要意义。
