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Nitrosomonas | |
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N. eutropha | |
Scientific classification | |
Domain: | Bacteria |
Phylum: | Pseudomonadota |
Class: | Betaproteobacteria |
Order: | Spirillales |
Family: | Nitrosomonadaceae |
Genus: | Nitrosomonas Winogradsky, 1892 [1] |
Type species | |
Nitrosomonas europaea | |
Species [2] | |
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Nitrosomonas is a genus of Gram-negative bacteria, belonging to the Betaproteobacteria. It is one of the five genera of ammonia-oxidizing bacteria [8] and, as an obligate chemolithoautotroph, [9] 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, [10] 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. [11] This microbe is photophobic, and usually generate a biofilm matrix, or form clumps with other microbes, to avoid light. [12] 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 . [13]
All species included in this genus have ellipsoidal or rod-shaped cells in which are present extensive intracytoplasmic membranes displaying as flattened vesicles. [8]
Most species are motile with a flagellum located in the polar region of the cell. Three basic morphological types of Nitrosomonas were studied, which are: short rods Nitrosomonas, rods Nitrosomonas and Nitrosomonas with pointed ends. Nitrosomonas species cells have different criteria of size and shape: [13]
Genome sequencing of Nitrosomonas species has been important to understand the ecological role of these bacteria. [11]
Among the various species of Nitrosomonas that are known today, the complete genomes of N. ureae strain Nm10, and N. europaea, N.sp. Is79 have been sequenced. [14]
The presence of the genes for ammonia oxidation characterizes all these species. The first enzyme involved in the ammonia oxidation is ammonia monooxygenase (AMO), which is encoded by the amoCAB operon. The AMO enzyme catalyzes the oxidation from (ammonia) to (hydroxylamine). The amoCAB operon contains three different genes: amoA, amoB and amoC. While N. europaea presents two copy of the genes, N. sp. Is79 and N. ureae strain Nm10 have three copy of these genes. [15] [16]
The second enzyme involved in the ammonia oxidation is hydroxylamine oxidoreductase (HAO), encoded by the hao operon. This enzyme catalyzes the oxidation from to , [17] a highly reactive radical intermediate that can be partitioned into both of the main AOB products: , a potent greenhouse gas, and , a form of nitrogen more bioavailable for crops, but that conversely washes away from fields faster. [18] The hao operon contains different genes such as the haoA, that encodes for the functional cytochrome c subunit, the cycA that encodes for cytochrome c554 and the gene cycB that encodes for quinone reductase. [15] These genes are present in different copies in various species; for instance, in Nitrosomonas sp. Is79 there are only three copies, while in N. ureae there are four. [19]
Important was the discovery of genes that encodes for enzymes involved in the denitrification. The first gene involved in this process is nirK that encodes for a nitrite reductase with copper. This enzyme catalyzes the reduction form (nitrite) to (nitric oxide). While in N. europaea, N. eutropha and N. cryotolerans nirK is included in a multigenetic cluster, [20] in Nitrosomonas sp. Is79 and N. sp. AL212, it is present as a single gene. [21] A high expression of the nirK gene was found in N.ureae and this has been explained with the hypothesis that the NirK enzyme is also involved in the oxidation of in this species. [22] The second genes involved in the denitrification are norCBQD that decode for a nitric-oxide reductase that catalyze the reduction from (nitric oxide) to (nitrous oxide). These genes are present in N. sp. AL212, N.cryotolerans and N. communis strain Nm2. In the Nitrosomonas europaea these genes are included in a cluster. [23] These genes are absent in N. sp. Is79 and N. ureae. [15] Recently is found the norSY gene that encodes for a nitric-oxide reductase with copper in N. communis strain Nm2 and Nitrosomonas AL212 [24] [25] .
Nitrosomonas uses the Calvin-Benson cycle as a pathway for the Carbon fixation. For this reason all the species present an operon that encodes for the RuBisCO enzyme. [21] A peculiarity is found in N. sp Is79 in which the two copies of the operon encode for two different forms of the RuBisCO: the IA form and the IC form, where the first one has major affinity with the Carbon dioxide. Other species present different copies of this operon that encode only for the IA form. [15] In N. europaea was found an operon characterized by five genes (ccbL, ccbS, ccbQ, ccbO and ccbN) that encodes for the RuBisCO enzyme. ccbL gene encodes for the major subunit while ccbS encodes for the minor subunit, these genes are also the most expressed. ccbQ and ccbO genes encoding for a number of proteins involved in the mechanisms of processing, folding, assembling, activation and regulation of the RuBisCO, instead ccbN, encodes for a protein of 101 amino acids, whose function is not known yet. Over these genes has been highlighted the presence of an assumed regulatory gene ccbR (transcribed in opposite direction to other genes) placed at 194 bp upstream of the ccbL gene start coding. [26]
Since Nitrosomonas are part of the AOB, ammonia carriers are important to them. Bacteria adapted to high concentrations of ammonia can absorb it passively by simple diffusion. Indeed, N. eutropha, that is adapted to high levels of ammonia doesn't present genes that encode for ammonia transporter. [27] Bacteria adapted to low concentrations of ammonia, present transporter (transmembrane protein) for this substrate. In Nitrosomonas two different carriers for ammonia have been identified, differing in structure and function. The first transporter is the Amt protein (amtB type) encoded by amt genes and this was found in Nitrosomonas sp. Is79. [15] The activity of this ammonia carrier depends on the membrane potential. [27] The second was found in N. europaea, where the rh1 gene is present which encodes an Rh-type ammonia carrier. Its activity is independent from the membrane potentia [27] l. Recent research has also linked Rh transmembrane proteins with transport, but it is not clear yet. [28]
Nitrosomonas is one of the genera included in the ammonia-oxidizing bacteria (AOB); AOB use ammonia as energy source and carbon dioxide as the main source of carbon. [29] The oxidation of ammonia is a rate-limiting step in nitrification and plays a fundamental role in the nitrogen cycle, because it transforms ammonia, which is usually extremely volatile, into less volatile forms of nitrogen. [29]
Nitrosomonas oxidizes ammonia into nitrite in a metabolic process, known as nitritation (a step of nitrification). This process occurs with the accompanying reduction of an oxygen molecule to water (which requires four electrons), and the release of energy. [30] The oxidation of ammonia to hydroxylamine is catalyzed by ammonia monooxygenase (AMO), which is a membrane-bound, multisubstrate enzyme. In this reaction two electrons are required to reduce an oxygen atom to water: [31]
Since an ammonia molecule only releases two electrons when oxidized, it has been assumed that the other two necessary electrons come from the oxidation of hydroxylamine to nitrite, [32] which occurs in the periplasm and it is catalyzed by hydroxylamine oxidoreductase (HAO), a periplasm associated enzymes. [32]
Two of the four electrons released by the reaction, return to the AMO to convert the ammonia in hydroxylamine. [32] 1,65 of the two remaining electrons are available for the assimilation of nutrients and the generation of the proton gradient. [30] They pass through the cytochrom c552 to the cytochrome caa3, then to O2, which is the terminal acceptor; here they are reduced to form water. [13] The remaining 0,35 electrons are used to reduce NAD+ to NADH, to generate the proton gradient. [13]
Nitrite is the major nitrogen oxide produced in the process, but it has been observed that, when oxygen concentrations are low, [13] nitrous oxide and nitric oxide can also form, as by-products from the oxidation of hydroxylamine to nitrite. [30]
The species N. europaea has been identified as being able to degrade a variety of halogenated compounds including trichloroethylene, benzene, and vinyl chloride. [33]
Nitrosomonas is generally found in highest numbers in all habitat in which there is abundance of ammonia (environment with plentiful protein decomposition or in wastewater treatment), thrive in a pH range of 6.0–9.0, and a temperature range of 20–30 °C (68–86 °F). Some species can live and proliferate on monuments’ surface or on stone buildings’ walls, contributing to erosion of those surfaces. [12]
It is usually found in all types of waters, globally distributed in both eutrophic and oligotrophic freshwater and saltwater, emerging especially above all in shallow coastal sediments and under the upwelling zones, such as the Peruvian coast and the Arabian Sea, [34] [35] but can also be found in fertilized soils. [21]
Some Nitrosomonas species, such as N.europaea, possess the enzyme urease (which catalyzes the conversion of the urea into ammonia and carbon dioxide) and 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. [36]
In agriculture, nitrification made by Nitrosomonas represents a problem because the oxidized nitrite by ammonia can persist in the soil, leaching, and making it less available for plants. [37]
Nitrification can be slowed down by some inhibitors that are able to slow down the oxidation process of ammonia to nitrites by inhibiting the activity of bacteria of the genus Nitrosomonas and other ammonia-oxidizing bacteria, minimize or prevent the loss of nitrate. [37] [38] (Read more about inhibitors in the section 'Inhibitors of nitrification' on this page Nitrification)
Nitrosomonas is used in activated sludge in aerobic wastewater treatment; the reduction of nitrogen compounds in the water is given by nitrification treatment in order to avoid environmental issues, such as ammonia toxicity and groundwater contamination. Nitrogen, if present in high quantities can cause algal development, leading to eutrophication with degradation of oceans and lakes. [39]
Employing as wastewater treatment biological removal of nitrogen is obtained a lower economic expense and less damage caused to the environment compared to physical-chemical treatments. [39]
Nitrosomonas has also a role in biofilter systems, typically in association and collaboration with other microbes, to consume compounds such as or and recycle nutrients. These systems are used for various purposes but mainly for the elimination of odors from waste treatment. [29]
N. europaea is a non-pathogenic bacteria studied in connection with probiotic therapies. In this context, it may give aesthetic benefits in terms of reducing the appearance of wrinkles. [40] The effectiveness of probiotic products has been studied to explore why N. eutropha, which is a highly mobile bacterium, has become extinct from the normal flora of our skin. It has been studied in connection with the idea of having benefits through the repopulation and reintroduction of N. eutropha to the normal flora of human skin. [41]
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.
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 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.
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.
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, agricultural lands 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.
Nitrosopumilus is a genus of archaea. The type species, 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.
Hydroxylamine oxidoreductase (HAO) is an enzyme found in the prokaryotic genus Nitrosomonas. It plays a critically important role in the biogeochemical nitrogen cycle as part of the metabolism of ammonia-oxidizing bacteria.
Hydroxylamine dehydrogenase (EC 1.7.2.6, HAO (ambiguous)) is an enzyme with systematic name hydroxylamine:ferricytochrome-c oxidoreductase. This enzyme catalyses the following chemical reaction
Ammonia monooxygenase (EC 1.14.99.39, AMO) is an enzyme, which catalyses the following chemical reaction
Nitrososphaera is a mesophilic genus of ammonia-oxidizing Crenarchaeota. The first Nitrososphaera organism was discovered in garden soils at the University of Vienna leading to the categorization of a new genus, family, order and class of Archaea. This genus is contains three distinct species: N. viennensis, Ca. N. gargensis, and Ca N. evergladensis. Nitrososphaera are chemolithoautotrophs and have important biogeochemical roles as nitrifying organisms.
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.
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 been 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.
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.
Nitrospinota is a bacterial phylum. Despite only few described species, members of this phylum are major nitrite-oxidizing bacteria in surface waters in oceans. By oxidation of nitrite to nitrate they are important in the process of nitrification in marine environments.
Lisa Y. Stein is an American biologist who is a professor at the University of Alberta. Her research considers the microbiology of climate change. She was awarded the 2022 University of Alberta Killam Award for Excellence in Mentoring.