Nitrification

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Nitrogen cycle Nitrogen Cycle.svg
Nitrogen cycle

Nitrification is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms [1] or entirely within one organism, as in comammox bacteria. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea.

Contents

Microbiology

Ammonia oxidation

The process of nitrification begins with the first stage of ammonia oxidation, where ammonia (NH3) or ammonium (NH4+) get converted into nitrite (NO2-). This first stage is sometimes known as nitritation. It is performed by two groups of organisms, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA [2] ).

Ammonia-Oxidizing Bacteria

Ammonia-Oxidizing Bacteria (AOB) are typically Gram-negative bacteria and belong to Betaproteobacteria and Gammaproteobacteria [3] including the commonly studied genera including Nitrosomonas and Nitrococcus . They are known for their ability to utilize ammonia as an energy source and are prevalent in a wide range of environments, such as soils, aquatic systems, and wastewater treatment plants.

AOB possess enzymes called ammonia monooxygenases (AMOs), which are responsible for catalyzing the conversion of ammonia to hydroxylamine (NH2OH), a crucial intermediate in the process of nitrification. [4] This enzymatic activity is sensitive to environmental factors, such as pH, temperature, and oxygen availability.

AOB play a vital role in soil nitrification, making them key players in nutrient cycling. They contribute to the transformation of ammonia derived from organic matter decomposition or fertilizers into nitrite, which subsequently serves as a substrate for nitrite-oxidizing bacteria (NOB).

Ammonia-Oxidizing Archaea

Prior to the discovery of archaea capable of ammonia oxidation, ammonia-oxidizing bacteria (AOB) were considered the only organisms capable of ammonia oxidation. Since their discovery in 2005, [5] two isolates of AOAs have been cultivated: Nitrosopumilus maritimus [6] and Nitrososphaera viennensis. [7] When comparing AOB and AOA, AOA dominate in both soils and marine environments, [2] [8] [6] [9] [10] [11] suggesting that Nitrososphaerota (formerly Thaumarchaeota) may be greater contributors to ammonia oxidation in these environments. [2]

Crenarchaeol, which is generally thought to be produced exclusively by AOA (specifically Nitrososphaerota), has been proposed as a biomarker for AOA and ammonia oxidation. Crenarchaeol abundance has been found to track with seasonal blooms of AOA, suggesting that it may be appropriate to use crenarchaeol abundances as a proxy for AOA populations [12] and thus ammonia oxidation more broadly. However the discovery of Nitrososphaerota that are not obligate ammonia-oxidizers [13] complicates this conclusion, [14] as does one study that suggests that crenarchaeol may be produced by Marine Group II Euryarchaeota. [15]

Nitrite oxidation

The second step of nitrification is the oxidation of nitrite into nitrate. This process is sometimes known as nitratation. Nitrite oxidation is conducted by nitrite-oxidizing bacteria (NOB) from the taxa Nitrospirota , [16] Nitrospinota , [17] Pseudomonadota [18] and Chloroflexota . [19] NOB are typically present in soil, geothermal springs, freshwater and marine ecosystems.

Complete ammonia oxidation

Ammonia oxidation to nitrate in a single step within one organism was predicted in 2006 [20] and discovered in 2015 in the species Nitrospira inopinata . A pure culture of the organism was obtained in 2017, [21] representing a revolution in our understanding of the nitrification process.

History

The idea that oxidation of ammonia to nitrate is in fact a biological process was first given by Louis Pasteur in 1862. [22] Later in 1875, Alexander Müller, while conducting a quality assessment of water from wells in Berlin, noted that ammonium was stable in sterilized solutions but nitrified in natural waters. A. Müller put forward, that nitrification is thus performed by microorganisms. [23] In 1877, Jean-Jacques Schloesing and Achille Müntz, two French agricultural chemists working in Paris, proved that nitrification is indeed microbially mediated process by the experiments with liquid sewage and artificial soil matrix (sterilized sand with powdered chalk). [24] Their findings were confirmed soon (in 1878) by Robert Warington who was investigating nitrification ability of garden soil at the Rothamsted experimental station in Harpenden in England. [25] R. Warington made also the first observation that nitrification is a two-step process in 1879 [26] which was confirmed by John Munro in 1886. [27] Although at that time, it was believed that two-step nitrification is separated into distinct life phases or character traits of a single microorganism.

The first pure nitrifier (ammonia-oxidizing) was most probably isolated in 1890 by Percy Frankland and Grace Frankland, two English scientists from Scotland. [28] Before that, Warington, [25] Sergei Winogradsky [29] and the Franklands were only able to enrich cultures of nitrifiers. Frankland and Frankland succeeded with a system of serial dilutions with very low inoculum and long cultivation times counting in years. Sergei Winogradsky claimed pure culture isolation in the same year (1890), [29] but his culture was still co-culture of ammonia- and nitrite-oxidizing bacteria. [30] S. Winogradsky succeeded just one year later in 1891. [31]

In fact, during the serial dilutions ammonia-oxidizers and nitrite-oxidizers were unknowingly separated resulting in pure culture with ammonia-oxidation ability only. Thus Frankland and Frankland observed that these pure cultures lose ability to perform both steps. Loss of nitrite oxidation ability was observed already by R. Warington. [26] Cultivation of pure nitrite oxidizer happened later during 20th century, however it is not possible to be certain which cultures were without contaminants as all theoretically pure strains share same trait (nitrite consumption, nitrate production). [30]

Ecology

Both steps are producing energy to be coupled to ATP synthesis. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth. Some AOB possess the enzyme, urease, which catalyzes the conversion of the urea molecule to two ammonia molecules and one carbon dioxide molecule. Nitrosomonas europaea, as well as populations of soil-dwelling AOB, have been shown to assimilate the carbon dioxide released by the reaction to make biomass via the Calvin Cycle, and harvest energy by oxidizing ammonia (the other product of urease) to nitrite. This feature may explain enhanced growth of AOB in the presence of urea in acidic environments. [32]

In most environments, organisms are present that will complete both steps of the process, yielding nitrate as the final product. However, it is possible to design systems in which nitrite is formed (the Sharon process ).

Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia.

Nitrification also plays an important role in the removal of nitrogen from municipal wastewater. The conventional removal is nitrification, followed by denitrification. The cost of this process resides mainly in aeration (bringing oxygen in the reactor) and the addition of an external carbon source (e.g., methanol) for the denitrification.

Nitrification can also occur in drinking water. In distribution systems where chloramines are used as the secondary disinfectant, the presence of free ammonia can act as a substrate for ammonia-oxidizing microorganisms. The associated reactions can lead to the depletion of the disinfectant residual in the system. [33] The addition of chlorite ion to chloramine-treated water has been shown to control nitrification. [34] [35]

Together with ammonification, nitrification forms a mineralization process that refers to the complete decomposition of organic material, with the release of available nitrogen compounds. This replenishes the nitrogen cycle.

Nitrification in the marine environment

In the marine environment, nitrogen is often the limiting nutrient, so the nitrogen cycle in the ocean is of particular interest. [36] [37] The nitrification step of the cycle is of particular interest in the ocean because it creates nitrate, the primary form of nitrogen responsible for "new" production. Furthermore, as the ocean becomes enriched in anthropogenic CO2, the resulting decrease in pH could lead to decreasing rates of nitrification. Nitrification could potentially become a "bottleneck" in the nitrogen cycle. [38]

Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Diverse microbes are responsible for each step in the marine environment. Several groups of ammonia-oxidizing bacteria (AOB) are known in the marine environment, including Nitrosomonas , Nitrospira , and Nitrosococcus . All contain the functional gene ammonia monooxygenase (AMO) which, as its name implies, is responsible for the oxidation of ammonia. [2] [37] Subsequent metagenomic studies and cultivation approaches have revealed that some Thermoproteota (formerly Crenarchaeota) possess AMO. Thermoproteota are abundant in the ocean and some species have a 200 times greater affinity for ammonia than AOB, contrasting with the previous belief that AOB are primarily responsible for nitrification in the ocean. [39] [36] Furthermore, though nitrification is classically thought to be vertically separated from primary production because the oxidation of nitrate by bacteria is inhibited by light, nitrification by AOA does not appear to be light inhibited, meaning that nitrification is occurring throughout the water column, challenging the classical definitions of "new" and "recycled" production. [36]

In the second step, nitrite is oxidized to nitrate. In the oceans, this step is not as well understood as the first, but the bacteria Nitrospina [17] [40] and Nitrobacter are known to carry out this step in the ocean. [36]

Chemistry and enzymology

Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms), and is catalyzed step-wise by a series of enzymes.

( Nitrosomonas , Comammox )
( Nitrobacter , Nitrospira , Comammox )

OR

In Nitrosomonas europaea , the first step of oxidation (ammonia to hydroxylamine) is carried out by the enzyme ammonia monooxygenase (AMO).

The second step (hydroxylamine to nitrite) is catalyzed by two enzymes. Hydroxylamine oxidoreductase (HAO), converts hydroxylamine to nitric oxide. [41]

Another currently unknown enzyme converts nitric oxide to nitrite.

The third step (nitrite to nitrate) is completed in a distinct organism.

Factors Affecting Nitrification Rates

Soil conditions

Due to its inherent microbial nature, nitrification in soils is greatly susceptible to soil conditions. In general, soil nitrification will proceed at optimal rates if the conditions for the microbial communities foster healthy microbial growth and activity. Soil conditions that have an effect on nitrification rates include:

Inhibitors of nitrification

Nitrification inhibitors are chemical compounds that slow the nitrification of ammonia, ammonium-containing, or urea-containing fertilizers, which are applied to soil as fertilizers. These inhibitors can help reduce losses of nitrogen in soil that would otherwise be used by crops. Nitrification inhibitors are used widely, being added to approximately 50% of the fall-applied anhydrous ammonia in states in the U.S., like Illinois. [42] They are usually effective in increasing recovery of nitrogen fertilizer in row crops, but the level of effectiveness depends on external conditions and their benefits are most likely to be seen at less than optimal nitrogen rates. [43]

The environmental concerns of nitrification also contribute to interest in the use of nitrification inhibitors: the primary product, nitrate, leaches into groundwater, producing toxicity in both humans [44] and some species of wildlife and contributing to the eutrophication of standing water. Some inhibitors of nitrification also inhibit the production of methane, a greenhouse gas.

The inhibition of the nitrification process is primarily facilitated by the selection and inhibition/destruction of the bacteria that oxidize ammonia compounds. A multitude of compounds that inhibit nitrification, which can be divided into the following areas: the active site of ammonia monooxygenase (AMO), mechanistic inhibitors, and the process of N-heterocyclic compounds. The process for the latter of the three is not yet widely understood, but is prominent. The presence of AMO has been confirmed on many substrates that are nitrogen inhibitors such as dicyandiamide, ammonium thiosulfate, and nitrapyrin.

The conversion of ammonia to hydroxylamine is the first step in nitrification, where AH2 represents a range of potential electron donors.

NH3 + AH2 + O2 → NH2OH + A + H2O

This reaction is catalyzed by AMO. Inhibitors of this reaction bind to the active site on AMO and prevent or delay the process. The process of oxidation of ammonia by AMO is regarded with importance due to the fact that other processes require the co-oxidation of NH3 for a supply of reducing equivalents. This is usually supplied by the compound hydroxylamine oxidoreductase (HAO) which catalyzes the reaction:

NH2OH + H2O → NO2− + 5 H+ + 4 e−

The mechanism of inhibition is complicated by this requirement. Kinetic analysis of the inhibition of NH3 oxidation has shown that the substrates of AMO have shown kinetics ranging from competitive to noncompetitive. The binding and oxidation can occur on two sites on AMO: in competitive substrates, binding and oxidation occurs at the NH3 site, while in noncompetitive substrates it occurs at another site.

Mechanism based inhibitors can be defined as compounds that interrupt the normal reaction catalyzed by an enzyme. This method occurs by the inactivation of the enzyme via covalent modification of the product, which ultimately inhibits nitrification. Through the process, AMO is deactivated and one or more proteins is covalently bonded to the final product. This is found to be most prominent in a broad range of sulfur or acetylenic compounds.

Sulfur-containing compounds, including ammonium thiosulfate (a popular inhibitor) are found to operate by producing volatile compounds with strong inhibitory effects such as carbon disulfide and thiourea.

In particular, thiophosphoryl triamide has been a notable addition where it has the dual purpose of inhibiting both the production of urease and nitrification. [45] In a study of inhibitory effects of oxidation by the bacteria Nitrosomonas europaea, the use of thioethers resulted in the oxidation of these compounds to sulfoxides, where the S atom is the primary site of oxidation by AMO. This is most strongly correlated to the field of competitive inhibition.

Examples of N-heterocyclic molecules. Nheterocyclicmolecules.png
Examples of N-heterocyclic molecules.

N-heterocyclic compounds are also highly effective nitrification inhibitors and are often classified by their ring structure. The mode of action for these compounds is not well understood: while nitrapyrin, a widely used inhibitor and substrate of AMO, is a weak mechanism-based inhibitor of said enzyme, the effects of said mechanism are unable to correlate directly with the compound's ability to inhibit nitrification. It is suggested that nitrapyrin acts against the monooxygenase enzyme within the bacteria, preventing growth and CH4/NH4 oxidation. [46] Compounds containing two or three adjacent ring N atoms (pyridazine, pyrazole, indazole) tend to have a significantly higher inhibition effect than compounds containing non-adjacent N atoms or singular ring N atoms (pyridine, pyrrole). [47] This suggests that the presence of ring N atoms is directly correlated with the inhibition effect of this class of compounds.

Methane oxidation inhibition

Some enzymatic nitrification inhibitors, such as nitrapyrin, can also inhibit the oxidation of methane in methanotrophic bacteria. [48] AMO shows similar kinetic turnover rates to methane monooxygenase (MMO) found in methanotrophs, indicating that MMO is a similar catalyst to AMO for the purpose of methane oxidation. Furthermore, methanotrophic bacteria share many similarities to NH3 oxidizers such as Nitrosomonas. [49] The inhibitor profile of particulate forms of MMO (pMMO) shows similarity to the profile of AMO, leading to similarity in properties between MMO in methanotrophs and AMO in autotrophs.

Environmental concerns

Nitrification process tank at a sewage treatment plant Nitrification Process Tank.jpg
Nitrification process tank at a sewage treatment plant

Nitrification inhibitors are also of interest from an environmental standpoint because of the production of nitrates and nitrous oxide from the process of nitrification. Nitrous oxide (N2O), although its atmospheric concentration is much lower than that of CO2, has a global warming potential of about 300 times greater than carbon dioxide and contributes 6% of planetary warming due to greenhouse gases. This compound is also notable for catalyzing the breakup of ozone in the stratosphere. [50] Nitrates, a toxic compound for wildlife and livestock and a product of nitrification, are also of concern.

Soil, consisting of polyanionic clays and silicates, generally has a net anionic charge. Consequently, ammonium (NH4+) binds tightly to the soil but nitrate ions (NO3−) do not. Because nitrate is more mobile, it leaches into groundwater supplies through agricultural runoff. Nitrates in groundwater can affect surface water concentrations, either through direct groundwater-surface water interactions (e.g., gaining stream reaches, springs), or from when it is extracted for surface use. As an example, much of the drinking water in the United States comes from groundwater, but most wastewater treatment plants discharge to surface water.

Wildlife such as amphibians, freshwater fish, and insects are sensitive to nitrate levels, and have been known to cause death and developmental anomalies in affected species. [51] Nitrate levels also contribute to eutrophication, a process in which large algal blooms reduce oxygen levels in bodies of water and lead to death in oxygen-consuming creatures due to anoxia. Nitrification is also thought to contribute to the formation of photochemical smog, ground level ozone, acid rain, changes in species diversity, and other undesirable processes. In addition, nitrification inhibitors have also been shown to suppress the oxidation of methane (CH4), a potent greenhouse gas, to CO2. Both nitrapyrin and acetylene are shown to be especially strong suppressors of both processes, although the modes of action distinguishing them are unclear.

See also

Related Research Articles

<span class="mw-page-title-main">Hydroxylamine</span> Inorganic compound

Hydroxylamine is an inorganic compound with the chemical formula NH2OH. The compound is in a form of a white hygroscopic crystals. Hydroxylamine is almost always provided and used as an aqueous solution. It is consumed almost exclusively to produce Nylon-6. The oxidation of NH3 to hydroxylamine is a step in biological nitrification.

<span class="mw-page-title-main">Anammox</span> Anaerobic ammonium oxidation, a microbial process of the nitrogen cycle

Anammox, an abbreviation for "anaerobic ammonium oxidation", is a globally important microbial process of the nitrogen cycle that takes place in many natural environments. The bacteria mediating this process were identified in 1999, and were a great surprise for the scientific community. In the anammox reaction, nitrite and ammonium ions are converted directly into diatomic nitrogen and water.

Nitrosomonas europaea is a Gram-negative obligate chemolithoautotroph that can derive all its energy and reductant for growth from the oxidation of ammonia to nitrite and lives in several places such as soil, sewage, freshwater, the walls of buildings and on the surface of monuments especially in polluted areas where the air contains high levels of nitrogen compounds.

<i>Nitrosomonas</i> Genus of bacteria

Nitrosomonas is a genus of Gram-negative bacteria, belonging to the Betaproteobacteria. It is one of the five genera of ammonia-oxidizing bacteria and, as an obligate chemolithoautotroph, uses ammonia as an energy source and carbon dioxide as a carbon source in presence of oxygen. Nitrosomonas are important in the global biogeochemical nitrogen cycle, since they increase the bioavailability of nitrogen to plants and in the denitrification, which is important for the release of nitrous oxide, a powerful greenhouse gas. This microbe is photophobic, and usually generate a biofilm matrix, or form clumps with other microbes, to avoid light. Nitrosomonas can be divided into six lineages: the first one includes the species Nitrosomonas europea, Nitrosomonas eutropha, Nitrosomonas halophila, and Nitrosomonas mobilis. The second lineage presents the species Nitrosomonas communis, N. sp. I and N. sp. II, meanwhile the third lineage includes only Nitrosomonas nitrosa. The fourth lineage includes the species Nitrosomonas ureae and Nitrosomonas oligotropha and the fifth and sixth lineages include the species Nitrosomonas marina, N. sp. III, Nitrosomonas estuarii and Nitrosomonas cryotolerans.

Denitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds such as nitrate and nitrite in the absence of oxygen as a terminal electron acceptor. They metabolize nitrogenous compounds using various enzymes, including nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (NOS), turning nitrogen oxides back to nitrogen gas or nitrous oxide.

<i>Nitrobacter</i> Genus of bacteria

Nitrobacter is a genus comprising rod-shaped, gram-negative, and chemoautotrophic bacteria. The name Nitrobacter derives from the Latin neuter gender noun nitrum, nitri, alkalis; the Ancient Greek noun βακτηρία, βακτηρίᾱς, rod. They are non-motile and reproduce via budding or binary fission. Nitrobacter cells are obligate aerobes and have a doubling time of about 13 hours.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

Nitrifying bacteria are chemolithotrophic organisms that include species of genera such as Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrospina, Nitrospira and Nitrococcus. These bacteria get their energy from the oxidation of inorganic nitrogen compounds. Types include ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Many species of nitrifying bacteria have complex internal membrane systems that are the location for key enzymes in nitrification: ammonia monooxygenase, hydroxylamine oxidoreductase, and nitrite oxidoreductase.

Paracoccus denitrificans, is a coccoid bacterium known for its nitrate reducing properties, its ability to replicate under conditions of hypergravity and for being a relative of the eukaryotic mitochondrion.

Nitrospira translate into “a nitrate spiral” is a genus of bacteria within the monophyletic clade 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. 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, natural biological marine settings, water circulation biofilters in aquarium tanks, terrestrial systems, fresh and salt water ecosystems, and hot springs. Nitrospira is a ubiquitous bacterium that plays a role in the nitrogen cycle by performing nitrite oxidation in the second step of nitrification. 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. 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. However, due to their difficulty to be cultivated in laboratory settings, the entire genome was only sequenced in one species, Nitrospira defluvii. In addition, Nitrospira bacteria's 16S rRNA sequences are too dissimilar to use for PCR primers, thus some members go unnoticed. In addition, members of Nitrospira with the capabilities to perform complete nitrification has also been discovered and cultivated.

<i>Nitrosopumilus</i> Genus of archaea

Nitrosopumilus maritimus is an extremely common archaeon living in seawater. It is the first member of the Group 1a Nitrososphaerota to be isolated in pure culture. Gene sequences suggest that the Group 1a Nitrososphaerota are ubiquitous with the oligotrophic surface ocean and can be found in most non-coastal marine waters around the planet. It is one of the smallest living organisms at 0.2 micrometers in diameter. Cells in the species N. maritimus are shaped like peanuts and can be found both as individuals and in loose aggregates. They oxidize ammonia to nitrite and members of N. maritimus can oxidize ammonia at levels as low as 10 nanomolar, near the limit to sustain its life. Archaea in the species N. maritimus live in oxygen-depleted habitats. Oxygen needed for ammonia oxidation might be produced by novel pathway which generates oxygen and dinitrogen. N. maritimus is thus among organisms which are able to produce oxygen in dark.

Nitrite oxidoreductase is an enzyme involved in nitrification. It is the last step in the process of aerobic ammonia oxidation, which is carried out by two groups of nitrifying bacteria: ammonia oxidizers such as Nitrosospira, Nitrosomonas, and Nitrosococcus convert ammonia to nitrite, while nitrite oxidizers such as Nitrobacter and Nitrospira oxidize nitrite to nitrate. NXR is responsible for producing almost all nitrate found in nature.

<span class="mw-page-title-main">SHARON Wastewater Treatment</span>

SHARON is a sewage treatment process. A partial nitrification process of sewage treatment used for the removal of ammonia and organic nitrogen components from wastewater flow streams. The process results in stable nitrite formation, rather than complete oxidation to nitrate. Nitrate formation by nitrite oxidising bacteria (NOB) is prevented by adjusting temperature, pH, and retention time to select for nitrifying ammonia oxidising bacteria (AOB). Denitrification of waste streams utilizing SHARON reactors can proceed with an anoxic reduction, such as anammox.

Ammonia monooxygenase (EC 1.14.99.39, AMO) is an enzyme, which catalyses the following chemical reaction

Nitrospira moscoviensis was the second bacterium classified under the most diverse nitrite-oxidizing bacteria phylum, Nitrospirae. It is a gram-negative, non-motile, facultative lithoauthotropic bacterium that was discovered in Moscow, Russia in 1995. The genus name, Nitrospira, originates from the prefix “nitro” derived from nitrite, the microbe’s electron donor and “spira” meaning coil or spiral derived from the microbe’s shape. The species name, moscoviensis, is derived from Moscow, where the species was first discovered. N. moscoviensis could potentially be used in the production of bio-degradable polymers.

<span class="mw-page-title-main">Nitrapyrin</span> Chemical compound

Nitrapyrin is an organic compound with the formula ClC5H3NCCl3, and is described as a white crystalline solid with a sweet odor. It is used as a nitrification inhibitor and bactericide, which is applied to soils for the growing of agricultural crops since 1974. Nitrapyrin was put up for review by the EPA and deemed safe for use in 2005. Nitrapyrin is an effective nitrification inhibitor to the bacteria Nitrosomonas and has been shown to drastically the reduce the amount of N2O emissions from the soil.

Comammox is the name attributed to an organism that can convert ammonia into nitrite and then into nitrate through the process of nitrification. Nitrification has traditionally thought to be a two-step process, where ammonia-oxidizing bacteria and archaea oxidize ammonia to nitrite and then nitrite-oxidizing bacteria convert to nitrate. Complete conversion of ammonia into nitrate by a single microorganism was first predicted in 2006. In 2015 the presence of microorganisms that could carry out both conversion processes was discovered within the genus Nitrospira, and the nitrogen cycle was updated. Within the genus Nitrospira, the major ecosystems comammox are primarily found in natural aquifers and engineered ecosystems.

Nitrososphaera gargensis is a non-pathogenic, small coccus measuring 0.9 ± 0.3 μm in diameter. N. gargensis is observed in small abnormal cocci groupings and uses its archaella to move via chemotaxis. Being an Archaeon, Nitrososphaera gargensis has a cell membrane composed of crenarchaeol, its isomer, and a distinct glycerol dialkyl glycerol tetraether (GDGT), which is significant in identifying ammonia-oxidizing archaea (AOA). The organism plays a role in influencing ocean communities and food production.

<span class="mw-page-title-main">Cattle urine patches</span> Grass damage by cattle urine

Urine patches in cattle pastures generate large concentrations of the greenhouse gas nitrous oxide through nitrification and denitrification processes in urine-contaminated soils. Over the past few decades, the cattle population has increased more rapidly than the human population. Between the years 2000 and 2050, the cattle population is expected to increase from 1.5 billion to 2.6 billion. When large populations of cattle are packed into pastures, excessive amounts of urine soak into soils. This increases the rate at which nitrification and denitrification occur and produce nitrous oxide. Currently, nitrous oxide is one of the single most important ozone-depleting emissions and is expected to remain the largest throughout the 21st century.

Anammox is a wastewater treatment technique that removes nitrogen using anaerobic ammonium oxidation (anammox). This process is performed by anammox bacteria which are autotrophic, meaning they do not need organic carbon for their metabolism to function. Instead, the metabolism of anammox bacteria convert ammonium and nitrite into dinitrogen gas. Anammox bacteria are a wastewater treatment technique and wastewater treatment facilities are in the process of implementing anammox-based technologies to further enhance ammonia and nitrogen removal.

References

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