Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 3UU, United Kingdom.
Proc Natl Acad Sci U S A. 2011 Sep 20;108(38):15892-7. doi: 10.1073/pnas.1107196108. Epub 2011 Sep 6.
Nitrification is a fundamental component of the global nitrogen cycle and leads to significant fertilizer loss and atmospheric and groundwater pollution. Nitrification rates in acidic soils (pH < 5.5), which comprise 30% of the world's soils, equal or exceed those of neutral soils. Paradoxically, autotrophic ammonia oxidizing bacteria and archaea, which perform the first stage in nitrification, demonstrate little or no growth in suspended liquid culture below pH 6.5, at which ammonia availability is reduced by ionization. Here we report the discovery and cultivation of a chemolithotrophic, obligately acidophilic thaumarchaeal ammonia oxidizer, "Candidatus Nitrosotalea devanaterra," from an acidic agricultural soil. Phylogenetic analysis places the organism within a previously uncultivated thaumarchaeal lineage that has been observed in acidic soils. Growth of the organism is optimal in the pH range 4 to 5 and is restricted to the pH range 4 to 5.5, unlike all previously cultivated ammonia oxidizers. Growth of this organism and associated ammonia oxidation and autotrophy also occur during nitrification in soil at pH 4.5. The discovery of Nitrosotalea devanaterra provides a previously unsuspected explanation for high rates of nitrification in acidic soils, and confirms the vital role that thaumarchaea play in terrestrial nitrogen cycling. Growth at extremely low ammonia concentration (0.18 nM) also challenges accepted views on ammonia uptake and metabolism and indicates novel mechanisms for ammonia oxidation at low pH.
硝化作用是全球氮循环的一个基本组成部分，会导致大量肥料损失以及大气和地下水污染。在酸性土壤（pH 值小于 5.5）中，硝化作用速率与中性土壤相当或超过中性土壤，而酸性土壤占世界土壤的 30%。具有讽刺意味的是，在 pH 值低于 6.5 的悬浮液培养中，进行硝化作用第一步的自养氨氧化细菌和古菌的生长很少或没有，而在这个 pH 值下氨的可用性会因离子化而降低。在这里，我们报告了一种化能自养、专性嗜酸的氨氧化古菌“Candidatus Nitrosotalea devanaterra”的发现和培养，该古菌来自酸性农业土壤。系统发育分析将该生物体置于一个以前未培养的古菌谱系中，该谱系在酸性土壤中被观察到。该生物体的最佳生长范围在 pH 值 4 到 5 之间，并且仅限于 pH 值 4 到 5.5 之间，与所有以前培养的氨氧化菌不同。该生物体的生长以及相关的氨氧化和自养作用也会在 pH 值为 4.5 的土壤硝化过程中发生。Nitrosotalea devanaterra 的发现为酸性土壤中硝化作用速率高提供了一个以前未被怀疑的解释，并证实了古菌在陆地氮循环中所起的重要作用。在极低的氨浓度（0.18 nM）下的生长也对氨吸收和代谢的公认观点提出了挑战，并表明了在低 pH 值下氨氧化的新机制。
