Denitrification is a microbially facilitated process where nitrate (NO 3 ) is reduced and ultimately produces molecular nitrogen (N 2 ) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter . The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO 3 ), nitrite (NO 2 ), nitric oxide (NO), nitrous oxide (N 2 O) finally resulting in the production of dinitrogen (N 2 ) completing the nitrogen cycle . Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO 3 , reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N 2 O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.
26-840: The Burkholderiales are an order of Betaproteobacteria in the phylum Pseudomonadota . Like all Pseudomonadota , they are Gram-negative . They include several pathogenic bacteria, including species of Burkholderia , Bordetella , and Ralstonia . They also include Oxalobacter and related genera, which are unusual in using oxalic acid as their source of carbon. Other well-studied genera include Alcaligenes , Cupriavidus , Achromobacter , Comamonas , Delftia , Massilia , Duganella , Janthinobacterium , Polynucleobacter (important freshwater bacterioplankton ), non-pathogenic Paraburkholderia , Caballeronia , Polaromonas , Thiomonas , Collimonas , Hydrogenophaga , Sphaerotilus , Variovorax , Acidovorax , Rubrivivax and Rhodoferax (both members of
52-422: A class of Gram-negative bacteria , and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria). The Betaproteobacteria comprise over 75 genera and 400 species. Together, they represent a broad variety of metabolic strategies and occupy diverse environments, ranging from obligate pathogens living within host organisms to oligotrophic groundwater ecosystems. Whilst most members of
78-436: A co-factor for nitrite reductase and nitrous-oxide reductase , also promoted complete denitrification when added as a supplement. Besides nutrients and terrain, microbial community composition can also affect the ratio of complete denitrification, with prokaryotic phyla Actinomycetota and Thermoproteota being responsible for greater release of N 2 than N 2 O compared to other prokaryotes. Denitrification can lead to
104-517: A condition called isotopic fractionation in the soil environment. The two stable isotopes of nitrogen, N and N are both found in the sediment profiles. The lighter isotope of nitrogen, N, is preferred during denitrification, leaving the heavier nitrogen isotope, N, in the residual matter. This selectivity leads to the enrichment of N in the biomass compared to N. Moreover, the relative abundance of N can be analyzed to distinguish denitrification apart from other processes in nature. Denitrification
130-480: A process known as dissimilatory nitrate reduction to ammonium or DNRA , is also possible for organisms that have the nrf- gene . This is less common than denitrification in most ecosystems as a means of nitrate reduction. Other genes known in microorganisms which denitrify include nir (nitrite reductase) and nos (nitrous oxide reductase) among others; organisms identified as having these genes include Alcaligenes faecalis , Alcaligenes xylosoxidans , many in
156-694: Is commonly used to remove nitrogen from sewage and municipal wastewater . It is also an instrumental process in constructed wetlands and riparian zones for the prevention of groundwater pollution with nitrate resulting from excessive agricultural or residential fertilizer usage. Wood chip bioreactors have been studied since the 2000s and are effective in removing nitrate from agricultural run off and even manure. Reduction under anoxic conditions can also occur through process called anaerobic ammonium oxidation ( anammox ): In some wastewater treatment plants , compounds such as methanol , ethanol , acetate , glycerin , or proprietary products are added to
182-700: Is potentially dangerous because high ammonium content can lead to eutrophication . Biological wastewater treatment systems, as well as other biological ammonium-removing methods, depend on the metabolism of various Bacteria including members of the Nitrosomonadales of the Betaproteobacteria that perform nitrification to remove excessive ammonia from wastewater. The ammonia is first oxidized into nitrite , further oxidized to nitrate . A variety of other organisms then reduces nitrate into molecular nitrogen gas ( denitrification ), which leaves
208-649: The Burkholderiales , the Neisseriales , the Nitrosomonadales and the Rhodocyclales . The name " Procabacteriales " was also proposed for an order of endosymbionts of Acanthamoeba , but since they cannot be grown in culture and studies have been limited, the name has never been validly or effectively published, and thus is no more than a nickname without any standing in nomenclature. An extensive reclassification of families and orders of
234-951: The Nitrosomonadales . The four orders of the Betaproteobacteria are: Some members of the Betaproteobacteria can cause disease in various eukaryotic organisms, including humans. For example, Neisseria gonorrhoeae and N. meningitidis cause gonorrhea and meningitis respectively, while Bordetella pertussis causes whooping cough . Other members of the class infect plants, such as Ralstonia solanacearum which causes bacterial wilt disease of over 250 plant species, Burkholderia cepacia which causes bulb rot in onions, and Xylophilus ampelinus which causes necrosis of grapevines. Betaproteobacteria play an important role in denitrification, removal of phosphorus, and xenobiotic degradation from waste. Various human activities, such as fertilizer production and chemical plant usage, release significant amounts of ammonium ions into rivers and oceans. Ammonium buildup in aquatic environments
260-607: The Betaproteobacteria are heterotrophic , deriving both their carbon and electrons from organocarbon sources, some are photoheterotrophic , deriving energy from light and carbon from organocarbon sources. Other genera are autotrophic , deriving their carbon from bicarbonate or carbon dioxide and their electrons from reduced inorganic ions such as nitrite , ammonium , thiosulfate or sulfide — many of these chemolithoautotrophic . Betaproteobacteria are economically important, with roles in maintaining soil pH and in elementary cycling. Some economically important members of
286-427: The Betaproteobacteria use nitrate as their terminal electron acceptor and can be used industrially to remove nitrate from wastewater by denitrification . A number of Betaproteobacteria are diazotrophs , meaning that they can fix molecular nitrogen from the air as their nitrogen source for growth – this is important to the farming industry as it is a primary means of ammonium levels in soils rising without
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#1732772722005312-404: The photosynthetic purple nonsulfur bacteria ), and Herbaspirillum (capable of nitrogen-fixation ). This Betaproteobacteria -related article is a stub . You can help Misplaced Pages by expanding it . Betaproteobacteria Burkholderiales Ferritrophicales Ferrovales Neisseriales Nitrosomonadales Procabacteriales Rhodocyclales Betaproteobacteria are
338-498: The alkalinity consumption in nitrification. A variety of non-biological methods can remove nitrate. These include methods that can destroy nitrogen compounds, such as chemical and electrochemical methods, and those that selectively transfer nitrate to a concentrated waste stream, such as ion exchange or reverse osmosis. Chemical removal of nitrate can occur through advanced oxidation processes, although it may produce hazardous byproducts. Electrochemical methods can remove nitrate by via
364-474: The bacteria is able to utilize nitrous oxide reductase , an enzyme that catalyzes the last step of denitrification. Aerobic denitrifiers are mainly Gram-negative bacteria in the phylum Proteobacteria. Enzymes NapAB, NirS, NirK and NosZ are located in the periplasm, a wide space bordered by the cytoplasmic and the outer membrane in Gram-negative bacteria. A variety of environmental factors can influence
390-478: The class based on a polyphasic analysis (including 16S rRNA gene analyses and 53-protein ribosomal protein concatamer analyses using the rMLST Multilocus sequence typing system) was published in 2017, that removed the order Hydrogenophilales from the class and into a novel class of the " Pseudomonadota ", the Hydrogenophilalia . The same study also merged the former order Methylophilales into
416-479: The complete reduction of NO 3 to N 2 rather than releasing N 2 O as an end product. Soil pH and texture are both factors that can moderate denitrification, with higher pH levels driving the reaction more to completion. Nutrient composition, particularly the ratio of carbon to nitrogen, is a strong contributor to complete denitrification, with a 2:1 ratio of C:N being able to facilitate full nitrate reduction regardless of temperature or carbon source. Copper, as
442-445: The complete reduction of nitrate to N 2 , and more than one enzymatic pathway has been identified in the reduction process. The denitrification process does not only provide energy to the organism performing nitrate reduction to dinitrogen gas, but also some anaerobic ciliates can use denitrifying endosymbionts to gain energy similar to the use of mitochondria in oxygen respiring organisms. Direct reduction from nitrate to ammonium ,
468-497: The concentration of dissolved and freely available oxygen is depleted. In these areas, nitrate (NO 3 ) or nitrite ( NO 2 ) can be used as a substitute terminal electron acceptor instead of oxygen (O 2 ), a more energetically favourable electron acceptor. Terminal electron acceptor is a compound that gets reduced in the reaction by receiving electrons. Examples of anoxic environments can include soils , groundwater , wetlands , oil reservoirs, poorly ventilated corners of
494-428: The ecosystem and is carried into the atmosphere. Denitrification The process is performed primarily by heterotrophic bacteria (such as Paracoccus denitrificans and various pseudomonads ), although autotrophic denitrifiers have also been identified (e.g., Thiobacillus denitrificans ). Denitrifiers are represented in all main phylogenetic groups. Generally several species of bacteria are involved in
520-542: The genus Pseudomonas , Bradyrhizobium japonicum , and Blastobacter denitrificans . Denitrification generally proceeds through some combination of the following half reactions, with the enzyme catalyzing the reaction in parentheses: The complete process can be expressed as a net balanced redox reaction, where nitrate (NO 3 ) gets fully reduced to dinitrogen (N 2 ): In nature, denitrification can take place in both terrestrial and marine ecosystems . Typically, denitrification occurs in anoxic environments, where
546-421: The industrial applications, including Electro-Biochemical Reactors (EBRs) , membrane bioreactors (MBRs), and moving bed bioreactors (MBBRs). Aerobic denitrification, conducted by aerobic denitrifiers, may offer the potential to eliminate the need for separate tanks and reduce sludge yield. There are less stringent alkalinity requirements because alkalinity generated during denitrification can partly compensate for
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#1732772722005572-513: The latter only has an observed limiting effect in wet soils. Oxygen likely affects denitrification in multiple ways—because most denitrifiers are facultative, oxygen can inhibit rates, but it can also stimulate denitrification by facilitating nitrification and the production of nitrate. In wetlands as well as deserts, moisture is an environmental limitation to rates of denitrification. Additionally, environmental factors can also influence whether denitrification proceeds to completion, characterized by
598-437: The ocean and seafloor sediments . Furthermore, denitrification can occur in oxic environments as well. High activity of denitrifiers can be observed in the intertidal zones, where the tidal cycles cause fluctuations of oxygen concentration in sandy coastal sediments. For example, the bacterial species Paracoccus denitrificans engages in denitrification under both oxic and anoxic conditions simultaneously. Upon oxygen exposure,
624-565: The presence of leguminous plants . The Betaproteobacteria are one of the eight classes that make up the Pseudomonadota ("Proteobacteria"). The Betaproteobacteria are most closely related to the Gammaproteobacteria , Acidithiobacillia and Hydrogenophilalia , which together make up a taxon which has previously been called " Chromatibacteria ". Four orders of Betaproteobacteria are currently recognised —
650-571: The rate of denitrification on an ecosystem-wide scale. For example, temperature and pH have been observed to impact denitrification rates. In the bacterial species, Pseudomonas mandelii , expression of denitrifying genes was reduced at temperatures below 30 °C and a pH below 5, while activity was largely unaffected between a pH of 6-8. Organic carbon as an electron donor is a common limiting nutrient for denitrification as observed in benthic sediments and wetlands. Nitrate and oxygen can also be potential limiting factors for denitrification, although
676-404: The wastewater to provide a carbon and electron source for denitrifying bacteria. The microbial ecology of such engineered denitrification processes is determined by the nature of the electron donor and the process operating conditions. Denitrification processes are also used in the treatment of industrial wastewater . Many denitrifying bioreactor types and designs are available commercially for
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