Ammonia Oxidising Archaea George Foot, Ke Meng & Dan Wilson
1. Introduction
Tweetable abstract: Archaea are now recognised as a dominant organism in the oxidation of ammonia #AOA #HR926EnviroMicrob @GeorgeKeDan
Figure 2: AOA & AOB abundance [ref. 10] Figure 1: Nitrogen cycle [ref. 1]
4. Atmospheric chemistry
5. Future research
AOA generate large amount of greenhouse gases such as methane and nitrous oxide [5]. Furthermore Nitrosopumilus maritimus has been demonstrated to be a biological source
of methylphosphonate. This could explain part of the high concentration of methane in
surface oceans [9].
3. Biochemistry
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2. The Thaumarchaeota
Figure captions Figure 1: Schematic of the global N cycle [1] Figure 2: Archaeal amoA genes compared to
bacterial amoA genes in a range of topsoils and deeper soil layers[10]
A fundamental component of the nitrogen cycle is nitrification (fig. 1).
This involves the biological oxidation of ammonia to nitrate. Until recently it had been assumed that ammonia oxidation was carried out exclusively by ammonia
oxidising bacteria (AOB) [1, 2]. However, subsequent research revealed that ammonia oxidizing archaea (AOA)
could be more significant in some environments [fig. 2; 1, 3]
In 2008 Brochier-Armanet et al. [4] suggested a third archaeal phylum characterised by the
ability to oxidise ammonia [5]. These archaea are ubiquitous [6]
and may therefore represent a significant component of global
ammonia oxidation.
The biochemistry of archaeal ammonia oxidation is unique and remains
unresolved. AOA share genes only distantly related to those encoding the
ammonia monooxygenase (AMO) of AOB. Currently there is no evidence that the
product of ammonia oxidation by AOA is hydroxylamine and in fact it has been
suggested that nitroxyl could instead be the product [7]. Nitroxyl may then be
oxidised to nitrite via a nitroxyl oxidoreductase [8]. Furthermore Nitric
oxide may also be important in the archaeal ammonia oxidation process.
Rapid development of genome sequencing will allow more efficient comparative studies
permitting for a greater understanding of the evolutionary origins of AOA.
Furthermore, future research should focus on furthering our understanding on AOA
biochemistry.
References: [1] Schleper, C. (2008). Metabolism of the deep. Nature, 456, 712-714. [2] Zhang, L. M., Offre, P. R., He, J. Z., Verhamme, D. T., Nicol, G. W., & Prosser, J. I. (2010). Autotrophic ammonia oxidation by soil thaumarchaea. Proceedings of the National Academy of Sciences, 107, 17240-17245. [3] Könneke, M., Bernhard, A.E., José, R., Walker, C.B., Waterbury, J.B., & Stahl, D.A. (2005). Isolation of an autotrophic ammonia-oxidizing marine archaeon. Nature, 437, 543-546. [4] Brochier-Armanet C, Boussau B, Gribaldo S, & Forterre P. (2008). Mesophilic Crenarchaeota: proposal for a third archaeal phylum, the Thaumarchaeota. Nat. Rev. Microbiol., 6, 245–52 [5] Stahl, D.A., & de la Torre, J.R. (2012). Physiology and diversity of ammonia-oxidizing archaea. Annual review of microbiology, 66, 83-101. [6] Offre, P., Spang, A., & Schleper, C. (2013). Archaea in biogeochemical cycles. Annu. Rev. Microbiol, 67, 437–57. [7] Walker CB ,de la Torre JR ,Klotz MG, Urakawa H,Pinel N,et al.(2010). Nitrosopumilus maritimus genome reveals unique mechanisms for nitrification and autotrophy in globally distributed marine crenarchaea. Proc. Natl. Acad. Sci., 107, 8818–23 [8] Hatzenpichler, R. (2012). Diversity, Physiology, and Niche Differentiation of Ammonia- Oxidizing Archaea. Applied and Environmental Microbiology. 78,21, 7501–7510. [9] Reeburgh W.S. (2007). Oceanic methane biogeochemistry. Chem. Rev., 107,486–513. [10] Leininger S, Urich T, Schloter M, Schwark L, Qi J, et al. (2006). Archaea predominate among ammonia-oxidizing prokaryotes in soils. Nature, 442, 806–9.