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Comammox (COMplete AMMonia OXidation) is the name attributed to an organism that can convert
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
into
nitrite The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also ...
and then into
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
through the process of
nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of ...
. 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 Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
into
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...
by a single
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
was first predicted in 2006. In 2015 the presence of microorganisms that could carry out both conversion processes was discovered within the genus ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
,'' and the
nitrogen cycle The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biolo ...
was updated. Within the genus ''Nitrospira,'' the major ecosystems comammox are primarily found in natural aquifers and engineered ecosystems. Complete nitrification step yield more energy (∆G°′ = −349 kJ mol−1 NH3) than either single oxidation alone (∆G°′ = −275 kJ mol−1 NH3 for ammonia oxidation to nitrite and ∆G°′ = −74 kJ mol−1 NO2 for nitrite oxidation to nitrate).


Comammox ''Nitrospira'' Bacteria

Complete nitrification of oxidizing ammonia to nitrate is energetically advantageous for ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
''. Due to the previous research done on ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
,'' it was thought that all ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
'' use nitrite as their energy source. Therefore, comammox ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
'' were not discovered until 2015. All discovered nitrifiers belong to sublineage II of the genus ''Nitrospira.'' The
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
of the nitrifying chemilithoautotrophic bacterium from the genus ''Nitrospira'' encodes for both ammonia and nitrite oxidation. The genes associated with the growth by ammonia oxidation to nitrate are
ammonia monooxygenase Ammonia monooxygenase (, ''AMO'') is an enzyme, which catalyses the following chemical reaction : ammonia + AH2 + O2 \rightleftharpoons NH2OH + A + H2O Ammonia monooxygenase contains copper and possibly nonheme iron. AMO is the first enzyme in ...
and hydroxylamine dehydrogenases genes (e.g.
amoA Ammonia monooxygenase (, ''AMO'') is an enzyme, which catalyses the following chemical reaction : ammonia + AH2 + O2 \rightleftharpoons NH2OH + A + H2O Ammonia monooxygenase contains copper and possibly nonheme iron. AMO is the first enzyme in ...
gene and hao cluster). This shows that complete nitrifying ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
'' serve as cornerstones of the nitrogen-cycling microbial communities found in the environment. Nearly two years after the discovery of comammox organisms, '' Nitrospira inopinata'' was the first complete nitrifier to be isolated in pure culture. Kinetic and physiological analysis of ''Nitrospira inopinata'' demonstrated that this complete nitrifier has a high affinity for ammonia, slow growth rate, low maximum rate of ammonia oxidation, and high yield. The discovery of comammox ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
'' provides a view into the modular evolution of the
nitrogen cycle The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biolo ...
and expands upon the complexity of the evolutionary history of
nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate occurring through separate organisms or direct ammonia oxidation to nitrate in comammox bacteria. The transformation of ...
.


Ecosystem of Comammox

Comammox have been identified in many ecosystems including natural
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...
and terrestrial ecosystems. Notably commamox genes were not found to be abundant in oceans. Additionally, the use of engineered ecosystems for comammox could be used for
ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...
removal during water and
wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environm ...
. Comammox have been found in many engineered systems including
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
biofiltration Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, a ...
units, drinking water treatment and distribution systems, and
wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environm ...
plants. The growth of comammox in these engineered ecosystems co-occur with ammonia-oxidizing bacteria and/or archaea, and usually outnumber other ammonia-oxidizing prokaryotes. The ecosystem of comammox is currently unknown in terms of
biogeography Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...
including their distribution and abundance due to the influences of process configuration and chemical composition of the treated wastewater. Following these findings, it was determined that comammox out-select ''
Nitrospira ''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 of the Nitrospirota phylum. The first member of this genus was d ...
'' in engineered environments, making comammox the ideal microorganism in use in
wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environm ...
processes.


See also

*
Anammox 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 gre ...


References

{{reflist Nitrogen cycle