Complete nitrification by a single microorganism.
Complete nitrification by a single microorganism.
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单个微生物完全硝化。
DOI：
10.1038/nature16459
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发表时间：
2015-12-24
期刊：
影响因子：
64.8
通讯作者：
Lücker S
中科院分区：
文献类型：
--
作者：
van Kessel MA;Speth DR;Albertsen M;Nielsen PH;Op den Camp HJ;Kartal B;Jetten MS;Lücker S
硝化是一个两步过程，其中氨被认为首先被氨氧化细菌（AOB）和/或古细菌（AOA）氧化为亚硝酸盐，随后被亚硝酸盐氧化细菌（NOB）氧化为硝酸盐。Winogradsky早在1890年就描述了这两个官能团之间的分工，这是地球化学氮循环的一个普遍接受的特征。氨在一种生物体中完全氧化成硝酸盐（完全氨氧化; comammox）在能量上是可行的，并且据推测，该过程可以在选择具有较低生长速率但比典型氨氧化微生物更高生长产量的物种的条件下发生。然而，尚未发现催化这一过程的生物。在这里，我们报告的富集和初步表征的两个Nitrospira物种编码的所有酶所需的氨氧化通过亚硝酸盐硝酸盐在其基因组中，并确实完全氧化铵硝酸盐，以节省能源。它们的氨单加氧酶（AMO）在遗传学上与目前鉴定的AMO不同，使得最近通过水平基因转移从已知的氨氧化微生物中获得不太可能。我们还在公共序列数据库中发现了高度相似的amoA序列（编码AMO亚基A），这些序列显然被错误地归类为甲烷单加氧酶。这种新的amoA序列组的识别将导致对氨氧化微生物的环境丰度和分布的更好的理解。此外，人们长期寻求的comammox过程的发现将改变我们对氮循环的看法。
Nitrification is a two-step process where ammonia is considered to first be oxidized to nitrite by ammonia-oxidizing bacteria (AOB) and/or archaea (AOA), and subsequently to nitrate by nitrite-oxidizing bacteria (NOB). Described by Winogradsky already in 1890, this division of labour between the two functional groups is a generally accepted characteristic of the biogeochemical nitrogen cycle. Complete oxidation of ammonia to nitrate in one organism (complete ammonia oxidation; comammox) is energetically feasible and it was postulated that this process could occur under conditions selecting for species with lower growth-rates but higher growth-yields than canonical ammonia-oxidizing microorganisms. Still, organisms catalysing this process have not yet been discovered. Here, we report the enrichment and initial characterization of two Nitrospira species that encode all enzymes necessary for ammonia oxidation via nitrite to nitrate in their genomes, and indeed completely oxidize ammonium to nitrate to conserve energy. Their ammonia monooxygenase (AMO) enzymes are phylogenetically distinct from currently identified AMOs, rendering recent acquisition by horizontal gene transfer from known ammonia-oxidizing microorganisms unlikely. We also found highly similar amoA sequences (encoding the AMO subunit A) in public sequence databases, which were apparently misclassified as methane monooxygenases. This recognition of a novel amoA sequence group will lead to an improved understanding on the environmental abundance and distribution of ammonia-oxidizing microorganisms. Furthermore, the discovery of the long-sought-after comammox process will change our perception of the nitrogen cycle.