Linking crenarchaeal activity to global nitrogen cycling in soil

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Microbes are key players in the turnover and transformation of nutrients, including carbon and nitrogen, in the environment. However, our understanding of these microbially mediated processes is severely hampered by our inability to culture the vast majority of microbes in the laboratory. The recent application of molecular techniques has circumvented these limitations, because they bypass the need for laboratory cultivation, and they have revolutionised our view of microbial diversity by enabling us to examine the 'uncultured majority'. Many groups of microbes have been discovered which have no representative in laboratory culture, and therefore no known ecosystem function, but which are abundant in natural environments. An important example is the mesophilic crenarchaea, which constitute approximately 6% of all prokaryotes in terrestrial and marine environments. Molecular techniques recently predicted that crenarchaea may have a central role in the oxidation of ammonia in the environment, a key step in the global nitrogen cycle, and an ammonia oxidising crenarchaea has since been isolated in the laboratory. As crenarchaea are a much more abundant than previously characterised ammonia-oxidising bacteria, they may represent the most important ammonia-oxidising organisms in the biosphere. This research proposal aims to quantify their role in ammonia oxidation in soil, to compare the impact of environmental factors on their activity and that of 'traditional' ammonia-oxidising organisms and to determine whether they possess distinct ecophysiological characteristics and ecology.