HR926 microbiology assessment

1. Ammonia Oxidising Archaea
George Foot, Ke Meng & Dan Wilson
Tweetable abstract: Archaea are now recognised as a dominant organism in the
oxidation of ammonia #AOA #HR926EnviroMicrob @GeorgeKeDan
1. Introduction
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]
2. The Thaumarchaeota
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.
3. Biochemistry
4. Atmospheric chemistry
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.
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].
5. Future research
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.
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]
Figure 1: Nitrogen cycle [ref. 1]
Figure 2: AOA & AOB abundance [ref. 10]

2. References:
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[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
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[7] Walker CB ,de la Torre JR ,Klotz MG, Urakawa H,Pinel N,et al.(2010). Nitrosopumilus maritimus genome reveals
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[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
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