Tolar Bradley B, Wallsgrove Natalie J, Popp Brian N, Hollibaugh James T
Department of Marine Sciences, University of Georgia, Athens, GA, 30602, USA.
Department of Microbiology, University of Georgia, Athens, GA, 30602, USA.
Environ Microbiol. 2017 Dec;19(12):4838-4850. doi: 10.1111/1462-2920.13457. Epub 2016 Aug 11.
Urea nitrogen has been proposed to contribute significantly to nitrification by marine thaumarchaeotes. These inferences are based on distributions of thaumarchaeote urease genes rather than activity measurements. We found that ammonia oxidation rates were always higher than oxidation rates of urea-derived N in samples from coastal Georgia, USA (means ± SEM: 382 ± 35 versus 73 ± 24 nmol L d , Mann-Whitney U-test p < 0.0001), and the South Atlantic Bight (20 ± 8.8 versus 2.2 ± 1.7 nmol L d , p = 0.026) but not the Gulf of Alaska (8.8 ± 4.0 versus 1.5 ± 0.6, p > 0.05). Urea-derived N was relatively more important in samples from Antarctic continental shelf waters, though the difference was not statistically significant (19.4 ± 4.8 versus 12.0 ± 2.7 nmol L d , p > 0.05). We found only weak correlations between oxidation rates of urea-derived N and the abundance or transcription of putative Thaumarchaeota ureC genes. Dependence on urea-derived N does not appear to be directly related to pH or ammonium concentrations. Competition experiments and release of NH suggest that urea is hydrolyzed to ammonia intracellularly, then a portion is lost to the dissolved pool. The contribution of urea-derived N to nitrification appears to be minor in temperate coastal waters, but may represent a significant portion of the nitrification flux in Antarctic coastal waters.
有人提出，尿素氮对海洋奇古菌的硝化作用有显著贡献。这些推论是基于奇古菌脲酶基因的分布，而非活性测量结果。我们发现，在美国佐治亚州沿海的样本中，氨氧化速率总是高于尿素衍生氮的氧化速率（平均值±标准误：382±35对73±24 nmol L⁻¹ d⁻¹，曼-惠特尼U检验p＜0.0001），在南大西洋湾也是如此（20±8.8对2.2±1.7 nmol L⁻¹ d⁻¹，p = 0.026），但在阿拉斯加湾并非如此（8.8±4.0对1.5±0.6，p＞0.05）。在南极大陆架水域的样本中，尿素衍生氮相对更重要，不过差异无统计学意义（19.4±4.8对12.0±2.7 nmol L⁻¹ d⁻¹，p＞0.05）。我们发现，尿素衍生氮的氧化速率与假定的奇古菌ureC基因的丰度或转录之间只有微弱的相关性。对尿素衍生氮的依赖性似乎与pH值或铵浓度没有直接关系。竞争实验和NH₃的释放表明，尿素在细胞内水解为氨，然后一部分氨进入溶解态。在温带沿海水域，尿素衍生氮对硝化作用的贡献似乎较小，但在南极沿海水域可能占硝化通量的很大一部分。
