Carbon and Nitrogen Utilization by Ammonia Oxidizing Archaea

Logan Hodgskiss, Melina Kerou, Christa Schleper

In the past decade, ammonia oxidizing archaea (AOA) have proven to be ubiquitous in soil environments. AOA are members of the Thaumarchaeota phylum and rely on ammonia oxidation as an energy source while growing autotrophically. Because of this,the core physiology of AOA contributes to both the global nitrogen and carbon cycles. However, little is known about the function and regulation of their primary metabolic processes. The recent isolation and genome annotation of an AOA from soil, Nitrososphaera viennensis, has set the stage to explore these questions. In pure culture, N. viennensis grows optimally at 42 ºC and is dependent on organic α-keto acids, such as pyruvate, for the detoxification of reactive oxygen species. Various growth experiments have been performed while varying the amount of nitrogen and carbon available for energy production and growth respectively. Preliminary transcriptomics results have demonstrated a strict reliance of carbon fixation gene expression, via the 3-hydroxypropionate/4-hydroxybutyrate cycle, on the presence of ammonium in culture media. This implies a physiological dependence of carbon cycle activity on nitrogen cycle activity in AOA. Limitation of inorganic carbon has also been shown to restrict the growth of N. viennensisin the absence of pyruvate. The pyruvate that is present likely creates a source of inorganic carbon via abiotic reactions with reactive oxygen species rather than acting as a source for mixotrophic growth. The dependence of N. viennensis on pyruvate has also been explored through the analysis of a mutant strain that is no longer dependent on pyruvate for growth. The results from the mutant strain, along with the growth responses under varying substrate conditions, should assist in elucidating the ecological role that AOA play in the environment.

Department für Ökogenomik und Systembiologie
ÖFOS 2012
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