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 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.