| Paracoccus denitrificans | |
|---|---|
Scientific classification  | |
| Domain: | Bacteria |
| Phylum: | Pseudomonadota |
| Class: | Alphaproteobacteria |
| Order: | Rhodobacterales |
| Family: | Rhodobacteraceae |
| Genus: | Paracoccus |
| Species: | P. denitrificans |
| Binomial name | |
| Paracoccus denitrificans Davis, 1969 | |
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 (endosymbiotic theory).
Paracoccus denitrificans, is a gram-negative, coccus, non-motile, denitrifying (nitrate-reducing) bacterium. It is typically a rod-shaped bacterium but assumes spherical shapes during the stationary phase. [1] 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. [2] The bacterium was reclassified in 1969 to Paracoccus denitrificans by D.H. Davis. [3] The genome of P. denitrificans was sequenced in 2004. [4]
Metabolically Paracoccus denitrificans is very flexible and has been recorded in soil in both aerobic 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. The 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. [1]
The denitrification properties of Paracoccus denitrificans are an important cause for the loss of nitrogen fertilisers in agricultural soil. This is possibly 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. [1] Although the enzymatic mechanisms of this denitrification process are well characterised, the exact molecular controles are yet to be fully described. [5] As such, Paracoccus denitrificans has emerged as an important model organism for the characterisation of the complete denitrification process in order to potentially reduce excessive nitrous oxide release from nitrogen fertilised soils. [6] [7]
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. [1]
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. [1]
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 oxidizes ammonia to nitrite, thus fueling the former metabolism. This system simplifies the process of removing nitrogen from wastewater. [8]
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 sulfonates under anaerobic growth conditions. [1]
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. [1]
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. [1]
Early research indicated that Paracoccus denitrificans especially resembled mitochondria. 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.[ citation needed ] 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. [9] More recent phylogenetic analysis however puts other bacteria more closely related to mitochondria: [10] see Proto-mitochondrion.
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 ultracentrifuge 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 hyper-acceleration which are usually found only in cosmic environments, such as on very massive stars or in the shock waves of supernovas. 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. [11] [12]
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 biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems.
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.
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) 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 (NO3−), nitrite (NO2−), nitric oxide (NO), nitrous oxide (N2O) finally resulting in the production of dinitrogen (N2) 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 NO3−, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N2O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.
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.
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 in absence of oxygen as a terminal electron acceptor. They metabolise nitrogenous compounds using various enzymes, turning nitrogen oxides back to nitrogen gas or nitrous oxide.
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.
Pseudomonas stutzeri is a Gram-negative soil bacterium that is motile, has a single polar flagellum, and is classified as bacillus, or rod-shaped. While this bacterium was first isolated from human spinal fluid, it has since been found in many different environments due to its various characteristics and metabolic capabilities. P. stutzeri is an opportunistic pathogen in clinical settings, although infections are rare. Based on 16S rRNA analysis, this bacterium has been placed in the P. stutzeri group, to which it lends its name.
Nitric oxide reductase, an enzyme, catalyzes the reduction of nitric oxide (NO) to nitrous oxide (N2O). The enzyme participates in nitrogen metabolism and in the microbial defense against nitric oxide toxicity. The catalyzed reaction may be dependent on different participating small molecules: Cytochrome c (EC: 1.7.2.5, Nitric oxide reductase (cytochrome c)), NADPH (EC:1.7.1.14), or Menaquinone (EC:1.7.5.2).
In enzymology, a nitrous oxide reductase also known as nitrogen:acceptor oxidoreductase (N2O-forming) is an enzyme that catalyzes the final step in bacterial denitrification, the reduction of nitrous oxide to dinitrogen.
Aerobic denitrification or co-respiration the simultaneous use of both oxygen (O2) and nitrate (NO3−) as oxidizing agents, performed by various genera of microorganisms. This process differs from anaerobic denitrification not only in its insensitivity to the presence of oxygen, but also in that it has a higher potential to create the harmful byproduct nitrous oxide.
CandidatusScalindua wagneri is a Gram-negative coccoid-shaped bacterium that was first isolated from a wastewater treatment plant. This bacterium is an obligate anaerobic chemolithotroph that undergoes anaerobic ammonium oxidation (anammox). It can be used in the wastewater treatment industry in nitrogen reactors to remove nitrogenous wastes from wastewater without contributing to fixed nitrogen loss and greenhouse gas emission.
Sulfurimonas is a bacterial genus within the class of Campylobacterota, known for reducing nitrate, oxidizing both sulfur and hydrogen, and containing Group IV hydrogenases. This genus consists of four species: Sulfurimonas autorophica, Sulfurimonas denitrificans, Sulfurimonas gotlandica, and Sulfurimonas paralvinellae. The genus' name is derived from "sulfur" in Latin and "monas" from Greek, together meaning a “sulfur-oxidizing rod”. The size of the bacteria varies between about 1.5-2.5 μm in length and 0.5-1.0 μm in width. Members of the genus Sulfurimonas are found in a variety of different environments which include deep sea-vents, marine sediments, and terrestrial habitats. Their ability to survive in extreme conditions is attributed to multiple copies of one enzyme. Phylogenetic analysis suggests that members of the genus Sulfurimonas have limited dispersal ability and its speciation was affected by geographical isolation rather than hydrothermal composition. Deep ocean currents affect the dispersal of Sulfurimonas spp., influencing its speciation. As shown in the MLSA report of deep-sea hydrothermal vents Campylobacterota, Sulfurimonas has a higher dispersal capability compared with deep sea hydrothermal vent thermophiles, indicating allopatric speciation.
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.
Dissimilatory nitrate reduction to ammonium (DNRA), also known as nitrate/nitrite ammonification, is the result of anaerobic respiration by chemoorganoheterotrophic microbes using nitrate (NO3−) as an electron acceptor for respiration. In anaerobic conditions microbes which undertake DNRA oxidise organic matter and use nitrate (rather than oxygen) as an electron acceptor, reducing it to nitrite, then ammonium (NO3−→NO2−→NH4+).
Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).
An oxygen minimum zone (OMZ) is characterized as an oxygen-deficient layer in the world's oceans. Typically found between 200m to 1500m deep below regions of high productivity, such as the western coasts of continents. OMZs can be seasonal following the spring-summer upwelling season. Upwelling of nutrient-rich water leads to high productivity and labile organic matter, that is respired by heterotrophs as it sinks down the water column. High respiration rates deplete the oxygen in the water column to concentrations of 2 mg/L or less forming the OMZ. OMZs are expanding, with increasing ocean deoxygenation. Under these oxygen-starved conditions, energy is diverted from higher trophic levels to microbial communities that have evolved to use other biogeochemical species instead of oxygen, these species include Nitrate, Nitrite, Sulphate etc. Several Bacteria and Archea have adapted to live in these environments by using these alternate chemical species and thrive. The most abundant phyla in OMZs are Pseudomonadota, Bacteroidota, Actinomycetota, and Planctomycetota.
Candidatus "Methylomirabilis oxyfera" is a candidate species of Gram-negative bacteria belonging to the NC10 phylum, characterized for its capacity to couple anaerobic methane oxidation with nitrite reduction in anoxic environments. To acquire oxygen for methane oxidation, M. oxyfera utilizes an intra-aerobic pathway through the reduction of nitrite (NO2) to dinitrogen (N2) and oxygen.