有氧氨氧化是全球氮循環(huán)中一個關(guān)鍵過程,。幾年前人們還認為，只有少數(shù)幾類細菌能夠催化這一反應(yīng),，但隨后廣泛分布的古細菌便被發(fā)現(xiàn)同樣也具有該功能,。
現(xiàn)在，對被稱為SCM1的海洋古細菌分離菌種所做的一項研究顯示,，它比細菌氨氧化劑對氨的親和力要高得多,。這一發(fā)現(xiàn)將可以解釋為什么海洋古細菌在寡營養(yǎng)海洋中能成功與其他微生物競爭,，并且還可支持這樣一個假說：硝化反應(yīng)在海洋氮循環(huán)中可能要比當前生物地化模型所假設(shè)的更為普遍。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
