Candidatus Nitrososphaera viennensis, an ammonia oxidizing archaeon from soil

Michaela Stieglmeier, Maria Tourna, Anja Spang, Christa Schleper

Ammonia oxidizing archaea have recently been discovered to be widespread in marine and terrestrial environments indicating that they play a major role in the global nitrogen cycle. Even though they are ubiquitous and dominate over ammonia oxidizing bacteria in many

environments, the isolation and cultivation of these chemolithoautotrophs is very challenging.

We report here on the first ammonia oxidizing archaeon cultivated from a terrestrial habitat, tentatively named Candidatus Nitrososphaera viennensis, which has been isolated from a garden soil in Vienna (Austria). Based on its 16S rRNA gene sequence it belongs to the soil group of ammonia oxidizing archaea and its closest cultivated relative is the moderately thermophile Candidatus Nitrososphaera viennensis. Growth experiments showed that several features clearly distinguish Ca. N. viennensis from its closest relative N. gargensis and from the more distantly related marine ammonia oxidizing archaeon Nitrosopumilus maritimus, as e.g. its adaptation to higher concentrations of ammonium (optimal concentration about 3mM; inhibition >10mM).

The doubling time of Ca. N. viennensis is about 40 hours and it reaches cell densities of at least 5 x 107 cells/ml. Various cultivation approaches are under way to explore the metabolic capacity of soil archaea, and to compare it to their bacterial counterparts, the ammonia oxidizing bacteria.

Our physiological investigations are supported by the draft genome sequence of Ca. N. viennensis which gives many indications for distinguishing features in these organisms.

ÖFOS 2012
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