Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, China), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
National Marine Environmental Monitoring Center, Laboratory of Island Ecological Environment Protection, Dalian 116023, China.
ISME J. 2024 Jan 8;18(1). doi: 10.1093/ismejo/wrae149.
The last two decades have seen nitrogen/iron-transforming bacteria at the forefront of new biogeochemical discoveries, such as anaerobic ammonium oxidation coupled to ferric iron reduction (feammox) and lithoautotrophic nitrate-reducing ferrous iron-oxidation (NRFeOx). These emerging findings continue to expand our knowledge of the nitrogen/iron cycle in nature and also highlight the need to re-understand the functional traits of the microorganisms involved. Here, as a proof-of-principle, we report compelling evidence for the capability of an NRFeOx enrichment culture to catalyze the feammox process. Our results demonstrate that the NRFeOx culture predominantly oxidizes NH4+ to nitrogen gas, by reducing both chelated nitrilotriacetic acid (NTA)-Fe(III) and poorly soluble Fe(III)-bearing minerals (γ-FeOOH) at pH 4.0 and 8.0, respectively. In the NRFeOx culture, Fe(II)-oxidizing bacteria of Rhodanobacter and Fe(III)-reducing bacteria of unclassified_Acidobacteriota coexisted. Their relative abundances were dynamically regulated by the supplemented iron sources. Metagenomic analysis revealed that the NRFeOx culture contained a complete set of denitrifying genes along with hao genes for ammonium oxidation. Additionally, numerous genes encoding extracellular electron transport-associated proteins or their homologs were identified, which facilitated the reduction of extracellular iron by this culture. More broadly, this work lightens the unexplored potential of specific microbial groups in driving nitrogen transformation through multiple pathways and highlights the essential role of microbial iron metabolism in the integral biogeochemical nitrogen cycle.
在过去的二十年中，氮/铁转化细菌一直处于新的生物地球化学发现的前沿，例如与三价铁还原偶联的厌氧氨氧化（feammox）和自养硝酸盐还原亚铁氧化（NRFeOx）。这些新出现的发现不断扩展了我们对自然界中氮/铁循环的认识，也强调了需要重新理解所涉及微生物的功能特征。在这里，作为一个原理验证，我们报告了确凿的证据，证明 NRFeOx 富集培养物能够催化 feammox 过程。我们的结果表明，NRFeOx 培养物主要通过还原螯合的三乙撑四胺五乙酸（NTA）-Fe（III）和难溶性含铁矿物（γ-FeOOH），将 NH4+氧化为氮气，分别在 pH 4.0 和 8.0 下进行。在 NRFeOx 培养物中，Rhodanobacter 中的亚铁氧化细菌和未分类的 Acidobacteriota 中的铁还原细菌共存。它们的相对丰度受补充铁源的动态调节。宏基因组分析显示，NRFeOx 培养物含有一套完整的反硝化基因以及用于铵氧化的 hao 基因。此外，还鉴定出了许多编码细胞外电子传输相关蛋白或其同源物的基因，这有助于该培养物还原细胞外铁。更广泛地说，这项工作揭示了特定微生物群体在通过多种途径驱动氮转化方面的未知潜力，并强调了微生物铁代谢在整体生物地球化学氮循环中的重要作用。
