Paracoccus denitrificans
Encyclopedia
Paracoccus denitrificans, is a coccoid bacterium known for its nitrate reducing properties, its ability to replicate under conditions of hypergravity
and for being the possible ancestor of the eukaryotic mitochondrion
(endosymbiotic theory
).
, coccoid, non-motile, denitrifying (nitrate-reducing) bacterium. It is typically a rod-shaped bacterium but assumes spherical shapes during the stationary phase. Like all gram-negative bacteria, it has a double membrane
with a cell wall. Formerly known as Micrococcus denitrificans, it was first isolated in 1910 by Martinus Beijerinck
, a Dutch
microbiologist
. The bacterium was reclassified in 1969 to Paracoccus denitrificans by D.H. Davis. The genome of P. denitrificans was sequenced in 2004.
or anaerobic
environments. The microbe also has the ability to live in many different kinds of media and environments and is known to be an extremophile
. Th bacteria are able to obtain energy both from organic compounds, such as methanol
and methylamine
, and from inorganic compounds, such as hydrogen
and sulfur
. The ability to metabolise compounds of hydrogen and sulfur, such as thiosulfate
has led to the microbe being exploited as a model organism for the study of poorly characterized sulfur compound transformations.
The denitrification
properties of Paracoccus denitrificans are an important cause for the loss of nitrogen fertilisers in agricultural soil. This is possible due to the chemical process called "denitrification" in which nitrogen is converted to dinitrogen to produce nitric oxide
and nitrous oxide
which cause damage to the atmosphere.
Metabolically, Paracoccus denitrificans is a known chemolithoautotroph - several strains of the microbe have been isolated that grow chemolithoautotrophically using carbon disulfide
or carbonyl sulfide
as energy sources. It is not a known human pathogen
.
Paracoccus is a biochemically versatile genus, possessing a variety of metabolisms through which a wide range of diverse compounds can be degraded. Accordingly, it has the potential for a wide variety of capabilities and applications in bioremediation
.
The denitrifying property of Paracoccus denitrificans has been used in creating a bioreactor, in this case, a tubular gel containing two bacteria, for the removal of nitrogen from wastewater. Paracoccus denitrificans reduces nitrite to nitrogen gas while Nitrosomonas europaea reduces ammonia to nitrite. This system simplifies the process of removing nitrogen from wastewater.
Certain strains of the microbe can utilize thiocyanate
as an energy source, a capability which could help clean thiocyanate-contaminated wastewater from coke-oven factories. Other strains have been discovered that can degrade halobenzoates under anaerobic denitrifying conditions, and that can degrade sulfonate
s under anaerobic growth conditions.
Strains of Paracoccus denitrificans have been isolated from activated sludge
that degrade a variety of methylated amines under both aerobic and anaerobic conditions; another strain is chemolithoautotrophically capable of degrading quaternary carbon compounds such as dimethylmalonate under denitrifying conditions.
Some strains are capable of 'aerobic denitrification', the complete dissimilation of nitrate to dinitrogen (or nitrous oxide) under aerobic growth conditions. The microbe also can oxidize ammonia
to nitrite while growth on organic energy sources, a process known as 'heterotrophic nitrification'. Coupled to denitrification, heterotrophic nitrification allows for the complete transformation of ammonia to dinitrogen by a single organism.
more closely than do other bacteria. The bacteria encloses within itself the biochemistry of the mitochondrial respiratory chain and oxidative phosphorylation. While these features are found randomly distributed in other species of aerobic bacteria, to date all of these are only found in Paracoccus denitrificans. In addition, a feasible mechanism for the evolution of a eukaryotic mitochondrion, from the plasma membrane of an ancestral aerobic bacterium resembling P. denitrificans to the inner mitochondrial membrane, has been suggested.
at high speeds corresponding to 403,627 times g
(the normal acceleration resulting from gravity at the Earth's surface). Paracoccus denitrificans displayed not only survival but also robust cellular growth under these conditions of hyperaccelaration which are usually found only in cosmic environments, such as on very massive stars or in the shock waves of supernova
s. Analysis showed that the small size of prokaryotic cells is essential for successful growth under hypergravity
. The research has implications on the feasibility of the existence of exobacteria and panspermia.
Hypergravity
Hypergravity is defined as the condition where the force of gravity exceeds that on the surface of the earth. This is expressed as being greater than 1 g...
and for being the possible ancestor of the eukaryotic mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
(endosymbiotic theory
Endosymbiotic theory
The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...
).
Description
Paracoccus denitrificans, is a gram-negativeGram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
, coccoid, non-motile, denitrifying (nitrate-reducing) bacterium. It is typically a rod-shaped bacterium but assumes spherical shapes during the stationary phase. Like all gram-negative bacteria, it has a double membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
with a cell wall. Formerly known as Micrococcus denitrificans, it was first isolated in 1910 by Martinus Beijerinck
Martinus Beijerinck
Martinus Willem Beijerinck was a Dutch microbiologist and botanist. Born in Amsterdam, Beijerinck studied at the Technical School of Delft, where he was awarded the degree of Chemical Engineer in 1872. He obtained his Doctor of Science degree from the University of Leiden in 1877...
, a Dutch
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
microbiologist
Microbiologist
A microbiologist is a scientist who works in the field of microbiology. Microbiologists study organisms called microbes. Microbes can take the form of bacteria, viruses, fungi, and protists...
. The bacterium was reclassified in 1969 to Paracoccus denitrificans by D.H. Davis. The genome of P. denitrificans was sequenced in 2004.
Ecology and ecological applications
Metabolically Paracoccus denitrificans is very flexible and has been recorded in soil in both aerobicAerobic
Aerobic is a word that means "requiring air", where "air" usually means oxygen.Aerobic may also refer to:* Aerobic exercise, prolonged exercise of moderate intensity* Aerobics, a form of aerobic exercise...
or anaerobic
Anaerobic
Anaerobic is a word which literally means without oxygen, as opposed to aerobic.In wastewater treatment the absence of oxygen is indicated as anoxic; and anaerobic is used to indicate the absence of a common electron acceptor such as nitrate, sulfate or oxygen.Anaerobic may refer to:*Anaerobic...
environments. The microbe also has the ability to live in many different kinds of media and environments and is known to be an extremophile
Extremophile
An extremophile is an organism that thrives in physically or geochemically extreme conditions that are detrimental to most life on Earth. In contrast, organisms that live in more moderate environments may be termed mesophiles or neutrophiles...
. Th bacteria are able to obtain energy both from organic compounds, such as methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
and methylamine
Methylamine
Methylamine is the organic compound with a formula of CH3NH2. This colourless gas is a derivative of ammonia, but with one H atom replaced by a methyl group. It is the simplest primary amine. It is sold as a solution in methanol, ethanol, THF, and water, or as the anhydrous gas in pressurized...
, and from inorganic compounds, such as hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
. The ability to metabolise compounds of hydrogen and sulfur, such as thiosulfate
Thiosulfate
Thiosulfate is an oxyanion of sulfur. The prefix thio indicates that thiosulfate ion is a sulfate ion with one oxygen replaced by a sulfur. Thiosulfate occurs naturally and is produced by certain biochemical processes...
has led to the microbe being exploited as a model organism for the study of poorly characterized sulfur compound transformations.
The denitrification
Denitrification
Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....
properties of Paracoccus denitrificans are an important cause for the loss of nitrogen fertilisers in agricultural soil. This is possible due to the chemical process called "denitrification" in which nitrogen is converted to dinitrogen to produce nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
and nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
which cause damage to the atmosphere.
Metabolically, Paracoccus denitrificans is a known chemolithoautotroph - several strains of the microbe have been isolated that grow chemolithoautotrophically using carbon disulfide
Carbon disulfide
Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
or carbonyl sulfide
Carbonyl sulfide
Carbonyl sulfide is the chemical compound with the formula OCS. Commonly written as COS, it is a colourless flammable gas with an unpleasant odor. It is a linear molecule consisting of a carbonyl group double bonded to a sulfur atom...
as energy sources. It is not a known human pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
.
Paracoccus is a biochemically versatile genus, possessing a variety of metabolisms through which a wide range of diverse compounds can be degraded. Accordingly, it has the potential for a wide variety of capabilities and applications in bioremediation
Bioremediation
Bioremediation is the use of microorganism metabolism to remove pollutants. Technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated...
.
The denitrifying property of Paracoccus denitrificans has been used in creating a bioreactor, in this case, a tubular gel containing two bacteria, for the removal of nitrogen from wastewater. Paracoccus denitrificans reduces nitrite to nitrogen gas while Nitrosomonas europaea reduces ammonia to nitrite. This system simplifies the process of removing nitrogen from wastewater.
Certain strains of the microbe can utilize thiocyanate
Thiocyanate
Thiocyanate is the anion [SCN]−. It is the conjugate base of thiocyanic acid. Common derivatives include the colourless salts potassium thiocyanate and sodium thiocyanate. Organic compounds containing the functional group SCN are also called thiocyanates...
as an energy source, a capability which could help clean thiocyanate-contaminated wastewater from coke-oven factories. Other strains have been discovered that can degrade halobenzoates under anaerobic denitrifying conditions, and that can degrade sulfonate
Sulfonate
A sulfonate is a salt or ester of a sulfonic acid. It contains the functional group R-SO2O-.- Sulfonate salts:Anions with the general formula RSO2O− are called sulfonates. They are the conjugate bases of sulfonic acids with formula RSO2OH. As sulfonic acids tend to be strong acids, the...
s under anaerobic growth conditions.
Strains of Paracoccus denitrificans have been isolated from activated sludge
Activated sludge
Activated sludge is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoans.-Purpose:...
that degrade a variety of methylated amines under both aerobic and anaerobic conditions; another strain is chemolithoautotrophically capable of degrading quaternary carbon compounds such as dimethylmalonate under denitrifying conditions.
Some strains are capable of 'aerobic denitrification', the complete dissimilation of nitrate to dinitrogen (or nitrous oxide) under aerobic growth conditions. The microbe also can oxidize ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
to nitrite while growth on organic energy sources, a process known as 'heterotrophic nitrification'. Coupled to denitrification, heterotrophic nitrification allows for the complete transformation of ammonia to dinitrogen by a single organism.
Resemblance to mitochondria
Research has indicated that Paracoccus denitrificans resembles a mitochondrionMitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
more closely than do other bacteria. The bacteria encloses within itself the biochemistry of the mitochondrial respiratory chain and oxidative phosphorylation. While these features are found randomly distributed in other species of aerobic bacteria, to date all of these are only found in Paracoccus denitrificans. In addition, a feasible mechanism for the evolution of a eukaryotic mitochondrion, from the plasma membrane of an ancestral aerobic bacterium resembling P. denitrificans to the inner mitochondrial membrane, has been suggested.
Growth under hypergravity
Recent research carried out on extremophiles in Japan involved a variety of bacteria including Paracoccus denitrificans being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifugeUltracentrifuge
The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 2,000,000 g . There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge...
at high speeds corresponding to 403,627 times g
Standard gravity
Standard gravity, or standard acceleration due to free fall, usually denoted by g0 or gn, is the nominal acceleration of an object in a vacuum near the surface of the Earth. It is defined as precisely , or about...
(the normal acceleration resulting from gravity at the Earth's surface). Paracoccus denitrificans displayed not only survival but also robust cellular growth under these conditions of hyperaccelaration which are usually found only in cosmic environments, such as on very massive stars or in the shock waves of supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
s. Analysis showed that the small size of prokaryotic cells is essential for successful growth under hypergravity
Hypergravity
Hypergravity is defined as the condition where the force of gravity exceeds that on the surface of the earth. This is expressed as being greater than 1 g...
. The research has implications on the feasibility of the existence of exobacteria and panspermia.
Further reading
- van Verseveld, H.W. and Stouthamer, A.H. (1999). The Genus Paracoccus. The Prokaryotes. 3rd edition, release 3.0. Springer-Verlag, New York. HTML