有氧氨氧化是全球氮循环中一个关键过程。几年前人们还认为，只有少数几类细菌能够催化这一反应，但随后广泛分布的古细菌便被发现同样也具有该功能。
现在，对被称为SCM1的海洋古细菌分离菌种所做的一项研究显示，它比细菌氨氧化剂对氨的亲和力要高得多。这一发现将可以解释为什么海洋古细菌在寡营养海洋中能成功与其他微生物竞争，并且还可支持这样一个假说：硝化反应在海洋氮循环中可能要比当前生物地化模型所假设的更为普遍。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 461, 976-979 (15 October 2009) | doi:10.1038/nature08465
Ammonia oxidation kinetics determine niche separation of nitrifying Archaea and Bacteria
Willm Martens-Habbena1, Paul M. Berube1,2, Hidetoshi Urakawa1, José R. de la Torre1,2 & David A. Stahl1
Department of Civil & Environmental Engineering, University of Washington, Seattle, Washington 98105, USA
Present addresses: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (P.M.B.); Department of Biology, San Francisco State University, San Francisco, California 94132, USA (J.R.T).
Correspondence to: Willm Martens-Habbena1David A. Stahl1 Correspondence and requests for materials should be addressed to W.M.-H. or D.A.S.
The discovery of ammonia oxidation by mesophilic and thermophilic Crenarchaeota and the widespread distribution of these organisms in marine and terrestrial environments indicated an important role for them in the global nitrogen cycle1, 2, 3, 4, 5, 6, 7. However, very little is known about their physiology or their contribution to nitrification8. Here we report oligotrophic ammonia oxidation kinetics and cellular characteristics of the mesophilic crenarchaeon 'Candidatus Nitrosopumilus maritimus' strain SCM1. Unlike characterized ammonia-oxidizing bacteria, SCM1 is adapted to life under extreme nutrient limitation, sustaining high specific oxidation rates at ammonium concentrations found in open oceans. Its half-saturation constant (K m = 133 nM total ammonium) and substrate threshold (10 nM) closely resemble kinetics of in situ nitrification in marine systems9, 10 and directly link ammonia-oxidizing Archaea to oligotrophic nitrification. The remarkably high specific affinity for reduced nitrogen (68,700 l per g cells per h) of SCM1 suggests that Nitrosopumilus-like ammonia-oxidizing Archaea could successfully compete with heterotrophic bacterioplankton and phytoplankton. Together these findings support the hypothesis that nitrification is more prevalent in the marine nitrogen cycle than accounted for in current biogeochemical models11.
