Evidence for Assimilatory Nitrate Reduction as a Previously Overlooked Pathway of Reactive Nitrogen Transformation in Estuarine Suspended Particulate Matter.
Evidence for Assimilatory Nitrate Reduction as a Previously Overlooked Pathway of Reactive Nitrogen Transformation in Estuarine Suspended Particulate Matter.
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DOI：
10.1021/acs.est.2c04390
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发表时间：
2022-09
影响因子：
11.4
通讯作者：
Ruiwen Hu;Songfeng Liu;Weiming Huang;Qiong Nan;P. Strong;M. Saleem;Zhen-Xin Zhou;Zhiwen Luo
中科院分区：
文献类型：
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作者：
Ruiwen Hu;Songfeng Liu;Weiming Huang;Qiong Nan;P. Strong;M. Saleem;Zhen-Xin Zhou;Zhiwen Luo
悬浮颗粒物 (SPM) 会导致河口生态系统中活性氮 (Nr) 的损失。尽管SPM中的反硝化和厌氧氨氧化补偿了当前全球氮（N）输入和汇的不平衡，但目前尚不清楚SPM中是否存在其他Nr转化途径。在这里，我们将稳定同位素测量与宏基因组学和宏转录组学相结合，以验证珠江口 SPM（PRE）中异化硝酸盐还原成铵（DNRA）的发生。令人惊讶的是，DNRA（nirBD）的常规功能基因在SPM中丰富且高表达，这与低潜在率不一致。通过分类学和比较基因组分析，我们证明亚硝酸盐还原酶 (NirBD) 与同化硝酸盐还原酶 (NasA) 结合在 SPM 中进行同化硝酸盐还原 (ANR)，并且不同的 α 和 γ 变形菌谱系被确定为关键的活性异养 ANR 细菌。此外，在对跨越 65 公里 PRE 的 SPM 中 Nr 转化途径的调查中，预计 ANR 的发生率相对高于反硝化和 DNRA。总的来说，这项研究描述了 SPM 中异养 ANR 细菌介导的以前被忽视的 Nr 转化途径，对于我们了解河口的 N 循环具有重要意义。
Suspended particulate matter (SPM) contributes to the loss of reactive nitrogen (Nr) in estuarine ecosystems. Although denitrification and anaerobic ammonium oxidation in SPM compensate for the current imbalance of global nitrogen (N) inputs and sinks, it is largely unclear whether other pathways for Nr transformation exist in SPM. Here, we combined stable isotope measurements with metagenomics and metatranscriptomics to verify the occurrence of dissimilatory nitrate reduction to ammonium (DNRA) in the SPM of the Pearl River Estuary (PRE). Surprisingly, the conventional functional genes of DNRA (nirBD) were abundant and highly expressed in SPM, which was inconsistent with a low potential rate. Through taxonomic and comparative genomic analyses, we demonstrated that nitrite reductase (NirBD) in conjunction with assimilatory nitrate reductase (NasA) performed assimilatory nitrate reduction (ANR) in SPM, and diverse alpha- and gamma-proteobacterial lineages were identified as key active heterotrophic ANR bacteria. Moreover, ANR was predicted to have a relative higher occurrence than denitrification and DNRA in a survey of Nr transformation pathways in SPM across the PRE spanning 65 km. Collectively, this study characterizes a previously overlooked pathway of Nr transformation mediated by heterotrophic ANR bacteria in SPM and has important implications for our understanding of N cycling in estuaries.