Nitrospira

Nitrospira
Scientific classification
Domain:	Bacteria
Phylum:	Nitrospirota
Class:	Nitrospira
Order:	Nitrospirales
Family:	Nitrospiraceae
Genus:	Nitrospira Watson et al. 1986
Type species
Nitrospira marina Watson et al. 1986
Species
See text

Nitrospira (from Latin: nitro, meaning "nitrate" and Greek: spira, meaning "spiral") translate into “a nitrate spiral” is a genus of bacteria within the monophyletic clade^[1] of the Nitrospirota phylum. The first member of this genus was described 1986 by Watson et al. isolated from the Gulf of Maine. The bacterium was named Nitrospira marina.^[2] Populations were initially thought to be limited to marine ecosystems, but it was later discovered to be well-suited for numerous habitats, including activated sludge of wastewater treatment systems,^[3] natural biological marine settings (such as the Seine River in France^[4] and beaches in Cape Cod^[5]), water circulation biofilters in aquarium tanks,^[4] terrestrial systems,^[5] fresh and salt water ecosystems, and hot springs.^[6] Nitrospira is a ubiquitous bacterium that plays a role in the nitrogen cycle^[7] by performing nitrite oxidation in the second step of nitrification.^[6] Nitrospira live in a wide array of environments including but not limited to, drinking water systems, waste treatment plants, rice paddies, forest soils, geothermal springs, and sponge tissue.^[8] Despite being abundant in many natural and engineered ecosystems Nitrospira are difficult to culture, so most knowledge of them is from molecular and genomic data.^[9] However, due to their difficulty to be cultivated in laboratory settings, the entire genome was only sequenced in one species, Nitrospira defluvii.^[10] In addition, Nitrospira bacteria's 16S rRNA sequences are too dissimilar to use for PCR primers, thus some members go unnoticed.^[9] In addition, members of Nitrospira with the capabilities to perform complete nitrification (comammox bacteria) has also been discovered^[8][11] and cultivated.^[12]

Morphology[edit]

For the following description, Nitrospira moscoviensis will be representative of the Nitrospira genus. Nitrospira is a gram-negative nitrite-oxidizing organism with a helical to vibroid morphology (0.9–2.2 × 0.2–0.4 micrometres in size).^[13] They are non-planktonic organisms that reside as clumps, known as aggregates, in biofilms.^[1] Visualization using transmission electron microscopy (TEM) confirms star-like protrusions on the outer membrane (6-8 nm thick). The periplasmic space is exceptionally wide (34-41 nm thick),^[5] which provides space to accommodate electron-rich molecules.^[14] Electron-deprived structures are located in the cytosol and are believed to be glycogen storage vesicles; polyhydroxybutyrate and polyphosphate granules are also identified in the cytoplasm.^[13] DNA analysis determined 56.9 +/- 0.4 mol% of the DNA to be guanine and cytosine base pairs.^[13]

General metabolism[edit]

Nitrospira are capable of aerobic hydrogen oxidation^[15] and nitrite oxidation^[6] to obtain electrons, but high concentrations of nitrite have shown to inhibit their growth.^[1] The optimal temperature for nitrite oxidation and growth in Nitrospira moscoviensis is 39 °C (can range from 33-44 °C) at a pH range of 7.6-8.0^[13] Despite being commonly classified as obligate chemolithotrophs,^[5] some are capable of mixotrophy.^[6] For instance, under different environments, Nitrospira can choose to assimilate carbon by carbon fixation^[6] or by consuming organic molecules (glycerol, pyruvate, or formate^[16]). New studies also show that Nitrospira can use urea as a source of nutrients.^[17] Urease encoded within their genome can break urea down to CO₂ and ammonia. The CO₂ can be assimilated by anabolism while the ammonia and organic by-product released by Nitrospira allow ammonium oxidizers^[6] and other microbes to co-exist in the same microenvironment.^[1]

Nitrification[edit]

All members of this genus have the nitrite oxidoreductase genes, and thus are all thought to be nitrite-oxidizers.^[9] Ever since nitrifying bacteria were discovered it was accepted that nitrification occurred in two steps, although it would be energetically favourable for one organism to do both steps.^[18] Recently Nitrospira members with the abilities to perform complete nitrification (comammox bacteria) have also been discovered^[8][11][19] and cultivated as in the case of Nitrospira inopinata.^[12] The discovery of commamox organisms within Nitrospira redefine the way bacteria contribute to the Nitrogen cycle and thus a lot of future studies will be dedicated to it.^[8]

With these new findings there's now a possibility to mainly use complete nitrification instead of partial nitrification in engineered systems like wastewater treatment plants because complete nitrification results in lower emissions of the greenhouse gases: nitrous oxide and nitric oxide, into the atmosphere.^[20]

Genome[edit]

After sequencing and analyzing the DNA of Nitrospira members researchers discovered both species had genes encoding ammonia monooxygenase (Amo) and hydroxlyamine dehydrogenase (hao), enzymes that ammonia-oxidizing bacteria (AOB), use to convert ammonia into nitrite.^[8][11][19] The bacteria possess all necessary sub-units for both enzymes as well as the necessary cell membrane associated proteins and transporters to carry out the first step of nitrification.^[8] Origins of the Amo gene are debatable as one study found that it is similar to other AOB[3], while another study found the Amo gene to be genetically distinct from other lineages.^[11] Current findings indicate that the hao gene is phylogenetically distinct from the hao gene present in other AOB, meaning that they acquired them long ago, likely by horizontal gene transfer.^[8]

Nitrospira also carry the genes encoding for all the sub-units of nitrite oxidoreductase (nxr), the enzyme that catalyzes the second step of nitrification.^[8]

Phylogeny[edit]

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN)^[21] and the National Center for Biotechnology Information (NCBI).^[22] Phylogeny is based on GTDB 08-RS214 by Genome Taxonomy Database^[23][24][25]

Species incertae sedis:

• "Ca. N. alkalitolerans" Daebeler et al. 2020
• "Ca. N. bockiana" Lebedeva et al. 2008
• "N. calida" Lebedeva et al. 2011
• N. marina Watson et al. 1986
• "Ca. N. salsa" Haaijer et al. 2013
• "N. tepida" Keuter et al. 2023

See also[edit]

• Nitrogen cycle
• List of bacterial orders
• List of bacteria genera

References[edit]

External links[edit]

• MicrobeWiki -- Nitrospira