Nitrososphaera viennensis

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A Microbial Biorealm page on the genus Nitrososphaera viennensis

Classification

Higher order taxa

Archaea; Thaumarchaeota; Nitrososphaerales; Nitrososphaeraceae

Species

Nitrososphaera viennensis

Nitrososphaera viennensis From: ScienceDaily

NCBI: Taxonomy

Description and significance

N. viennensis is a slightly irregular, spherically shaped ammonia oxidizing archaeon with a cell diameter of approximately 0.5-0.8 μm⁽²⁾. It was the first cultivated terrestrial archaeal ammonia oxidizer⁽²⁾.

Genome structure

The sequence divergence of N. viennensis's 16s rRNA gene from its closest relative, N. gargensis, is 3%⁽²⁾.

Ammonia oxidizing Bacteria aerobically oxidize ammonia using ammonia monooxygenase (amoA) to catalyze the initial oxidation of NH₃⁽¹⁾. Ammonia oxidizing archaea have amo-like genes that may contribute to their ammonia oxidation⁽¹⁾.

The urease gene cluster was located in one strain of N. viennensis, EN76⁽²⁾. The cluster consisted of the encoding subunits ureA, ureB, and ureC and the accessory proteins ureE, ureF, ureG, and ureD⁽²⁾.

NCBI: Genome

Metabolism

N. viennensis used urea or ammonia as an energy source in laboratory conditions⁽²⁾. It is able to grow chemolithoautotrohically with inorganic compounds as an electron donor, but displayed higher growth rates when grown with bacteria or with the addition of pyruvate⁽²⁾. It is currently unknown whether it is capable of heterotrophic or mixotrophic growth⁽²⁾. The addition of vitamins, amino acids, and sugars had only a marginal effect on growth⁽²⁾. Acetylene is a possible growth inhibitor⁽²⁾.

The electron transfer process is not fully understood yet in ammonia oxidizing archaea⁽¹⁾. The amount of ATP per mole of NH₃ is unknown since it varies depending on growth stage and other factors⁽¹⁾. Lack of cytochrome c proteins and many copper-containing proteins suggest a different electron transport mechanism than ammonia oxidizing bacteria, which is iron-heme-dependent⁽¹⁾.

Ecology

N. viennensis exists in soil globally⁽¹⁾. The first N. viennensis strain isolated was from garden soil from the University Center at Althanstrasse in Vienna's 9th District⁽³⁾.

Its optimal temperature is 35°C with an optimum pH of 7.5⁽²⁾. Generation time of a pure culture with 1mM ammonia and pyruvate was about ~45h⁽²⁾. Cell densities reached 5 X 10⁷ cells mL^-1(2). Growth on cultures with ammonium alone slowed down to ~23d demonstrating it can grow autotrophically exclusively although very slowly⁽²⁾.

It is able to withstand higher ammonia concentrations than other ammonia oxidizing archaea such as Nitrosopumilus maritimus and Nitrososphaera gargensis ⁽²⁾. Growth occurred at concentrations as high as 15 mM, but was inhibited at 20 mM⁽²⁾. Inhibitory ammonia concentrations for N. maritimus and N. gargensis are 2 to 3 mM. Ammonia tolerances were similar to oligotrophic bacterial ammonia oxidizers⁽²⁾.

Ammonia oxidizing Archaea such as N. viennensis may contribute to the nitrification of the environment⁽²⁾. It was previously believed only Bacteria could oxidize ammonia⁽²⁾. Ammonia oxidation is the first step in denitrification (NH₃ to NO_2-) ⁽¹⁾. Eventually N₂O is produced in this process and escapes into the environment ⁽¹⁾. N₂O has a greenhouse warming potential 310 times higher than CO₂⁽¹⁾. It is responsible for 5%-7% of the greenhouse effect⁽¹⁾. It is the third most important greenhouse gas after CO₂ and CH₄⁽¹⁾. Ammonia oxidizing Bacteria and Archaea are estimated to contribute to ~70% of global N₂O emissions⁽¹⁾.

References

1. Hatzenpichler, Roland (2012) Diversity, Physiology, and Niche Differentiation of Ammonia-Oxidizing Archaea, Applied and Environmental Microbiology 2012 Nov: 78(21): 7501-10. doi: 10.1128/AEM.01960-12.

2. Tourna, Maria, M. Stieglmeier, A. Spang, M. Könneke, A. Schintlmeister, T. Urich, M. Engel, M. Schloter, M. Wagner, A. Richter, and C. Schleper (2011) Nitrososphaera viennensis, an ammonia oxidizing archaeon from soil, PNAS 2011 ; doi:10.1073/pnas.1013488108

3. University of Vienna (2011) Novel microorganism 'Nitrososphaera viennensis' isolated. ScienceDaily, 2011 April 28. Retrieved April 28, 2013, from http://www.sciencedaily.com/releases/2011/04/110425153556.htm

Edited by Shanna Lovelace of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences, http://www.usm.maine.edu/bio