Complete nitrification by a single microorganism
By M. V. van Kessel, D. Speth, Mads Albertsen, Per Halkjær Nielsen, H. O. D. op den Camp, B. Kartal, M. Jetten, Sebastian Lücker. Nature, 2015
1,636 citations recorded by the source corpus.
Nitrification is a two-step process where ammonia is first oxidized to nitrite by ammonia-oxidizing bacteria and/or archaea, and subsequently to nitrate by nitrite-oxidizing bacteria. Already described by Winogradsky 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 the 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 of 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.
Subfields: Ecology, Molecular Biology, Pollution
View Paper: https://www.semanticscholar.org/paper/0870d73c57035ff237541b7672093832ef73128c
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Citations in the corpus
- Heterotrophic nitrifying bacteria in wastewater biological nitrogen removal systems: A review (2021, background): “…pathway by anaerobic AOB; and the heterotrophic aerobic ammonia oxidization (or heterotrophic nitrification) pathway by heterotrophic nitrifying bacteria (HNB; or heterotrophic AOB; Holmes et al., 2019; Jahangir et al., 2020; Van Kessel et al., 2015; Wen et al., 2020; Zhang, Zheng, et al., 2020).”
- Nitrification gene ratio and free ammonia explain nitrite and nitrous oxide production in urea-amended soils (2017, background): “Recently, some NOBwithin the genus Nitrospira have been found to be capable of oxidizing both NH4þ and NO2 (Daims et al., 2015; van Kessel et al., 2015), although the prevalence of bacteria with this metabolic capability, referred to as “complete nitrification” or “comammox,” in agricultural soils…”