Nitrososphaera

The Nitrososphaera genus are one of the first discovered ammonia-oxidizing archaea. Only three distinct species of this genus have been identified. Both Ca. N. gargensis, and Ca N. Evergladensis are known as Candidatus, which have been discovered and analyzed but have yet been studied in pure culture in a lab. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[2] and National Center for Biotechnology Information (NCBI) Cladogram was taken from GTDB release 07-RS207 (8th April 2022).

Nitrososphaera microbes have varying characteristics that is dependent on species. All three species present genes that cluster urease, urea, and ammonia.[6] As part of Archaea, these microbes have a cell membrane composed of crenarchaeol, its isomer, and a glycerol dialkyl glycerol tetraether (GDGT), all of which are used for identifying ammonia-oxidizing archaea.[7] N. viennensis has a cell diameter of approximately 0.6–0.9 µm and presents an irregular spherical coccus.[1][6] This species was first discovered of the Nitrososphaera genus. Ca. N. gargensis is non-pathogenic presents a diameter of approximately 0.9 ± 0.3 μm with a relatively small coccus.[8] Ca. N evergladensis has yet to be properly analyzed and described for morphological characteristics.  

Ammonia-oxidizing archaea has been found in various environments and habitats around the world. N. viennensis was first discovered in garden soils.[3] The preferred growth temperature is at approximately 35° C - 42° C with a pH of 7.5.[1] Ca. N. gargensis was found in hot springs and is commonly found in heavy metal containing habitats with a growth temperature within the ~ 46° C.[9] Ca. N evergladensis was first discovered in the humid region of the Everglades in Florida. Other relatives of Nitrososphaera sp. can also be found in swamps, microbial mats, freshwater sediments, deep sea marine sediments, and regions with high levels of nitrogen and ammonia sources to allow for the oxidation process of the lipids and nutrients for the optimal survival of these microbes.[4]

Microbial nitrogen cycle. Process by which ammonia is processed through microbial organisms for lipid and protein production.

It was believed until recently that only bacteria were capable of ammonia oxidation.[10] However, with the discovery of Nitrososphaera, it has been proven that some archaea are capable of ammonia oxidation as well. These archaea utilize ammonia from the environment, retrieved from soils, to transform it into ATP.[11] This process involves transforming ammonia (NH₃) into nitrite (NO₂^-). This promotes the nitrification of the environment surrounding the Nitrososphaera. Within nitrogen cycling in soils, the ammonia oxidation leads to the disaggregation of other chemical compounds, providing important nutrients for plant survival.[1] One of the chemical compounds that forms from nitrogen cycling is nitrous oxide (N₂O) emission, a gas that is released into the atmosphere as one of the Green House Gasses.[4][6] This gas is known for its radiative efficiency 216 larger than CO₂.[12] These ammonia-oxidizing archaea are a key component in soils that form more than 65% of the Earths atmospheric nitrous oxide concentrations.[13]