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.