Deinococcus radiodurans
Encyclopedia
Deinococcus radiodurans is an extremophilic
bacterium, one of the most radioresistant organisms known. It can survive cold, dehydration, vacuum, and acid
, and is therefore known as a polyextremophile
and has been listed as the world's toughest bacterium in The Guinness Book Of World Records
.
δεινός (deinos) and kokkos meaning "terrible grain" and the Latin
radius and durare, meaning "radiation surviving". The species was formerly called Micrococcus radiodurans. As a consequence of its hardiness, it has been nicknamed Conan the Bacterium
.
Initially, it was placed in the genus Micrococcus
. After evaluation of ribosomal
RNA
sequences and other evidence, it was placed in its own genus Deinococcus
, which is closely related to the genus Thermus of heat-resistant bacteria; the group consisting of the two is accordingly known as Deinococcus-Thermus
.
Deinococcus is the only genus in the order Deinococcales. D. radiodurans is the type species
of this genus, and the best studied member. All known members of the genus are radioresistant: D. proteolyticus, D. radiopugnans, D. radiophilus, D. grandis, D. indicus, D. frigens, D. saxicola, D. marmoris, D. deserti, D. geothermalis and D. murrayi; the latter two are also thermophilic
.
. Experiments were being performed to determine if canned food could be sterilized using high doses of gamma radiation. A tin of meat was exposed to a dose of radiation that was thought to kill all known forms of life, but the meat subsequently spoiled, and D. radiodurans was isolated.
The complete DNA sequence of D. radiodurans was published in 1999 by TIGR
. A detailed annotation and analysis of the genome appeared in 2001. The sequenced strain was ATCC BAA-816.
Deinococcus radiodurans has a unique quality in which it can repair both single- and double-stranded DNA. When a mutation is apparent to the cell, it brings it into a compartmental ring-like structure, where the DNA is repaired and then is able to fuse the nucleoids from the outside of the compartment with the damaged DNA.
. Four cells normally stick together, forming a tetrad. The bacteria are easily cultured and do not appear to cause disease. Colonies are smooth, convex, and pink to red in color. The cells stain Gram positive, although its cell envelope is unusual and is reminiscent of the cell walls of Gram negative bacteria.
D. radiodurans does not form endospore
s and is nonmotile. It is an obligate aerobic
chemoorganoheterotroph
, i.e., it uses oxygen
to derive energy from organic compounds in its environment. It is often found in habitats rich in organic materials, such as soil, feces, meat, or sewage, but has also been isolated from dried foods, room dust, medical instruments and textiles.
It is extremely resistant to ionizing radiation
, ultraviolet
light, desiccation
, and oxidizing and electrophilic
agents.
Its genome consists of two circular chromosome
s, one 2.65 million base pairs long and the other 412,000 base pairs long, as well as a megaplasmid
of 177,000 base pairs and a plasmid
of 46,000 base pairs. It has about 3,195 gene
s. In its stationary phase, each bacterial cell contains four copies of this genome; when rapidly multiplying, each bacterium contains 8-10 copies of the genome.
of ionizing radiation
with almost no loss of viability, and an acute dose of 15,000 Gy with 37% viability. A dose of 5,000 Gy is estimated to introduce several hundred double-strand breaks (DSBs) into the organism's DNA (~0.005 DSB/Gy/Mbp (haploid genome)). For comparison, a chest X-ray or Apollo mission involves about 1 mGy, 5 Gy can kill a human, 200-800 Gy will kill E. coli
, and over 4,000 Gy will kill the radiation-resistant tardigrade
.
Several bacteria of comparable radioresistance are now known, including some species of the genus Chroococcidiopsis
(phylum cyanobacteria) and some species of Rubrobacter
(phylum actinobacteria
); among the archaea
, the species Thermococcus
gammatolerans shows comparable radioresistance. Deinocuccus radiodurans also has a unique ability to repair damaged DNA. It isolates the damaged segments in a controlled area and repairs it. This bacteria can also repair many small fragments from an entire chromosome.
and rapid DNA repair
mechanisms. It usually repairs breaks in its chromosomes within 12–24 hours through a 2-step process. First, D. radiodurans reconnects some chromosome fragments through a process called single-stranded annealing. In the second step, a protein mends double-strand breaks through homologous recombination
. This process does not introduce any more mutations than a normal round of replication would.
A persistent question regarding D. radiodurans is how such a high degree of radioresistance could evolve. Natural background radiation
levels are very low—in most places, on the order of 0.4 mGy per year, and the highest known background radiation, near Ramsar, Iran
is only 260 mGy per year. With naturally-occurring background radiation levels so low, organisms evolving mechanisms specifically to ward off the effects of high radiation are unlikely.
Valerie Mattimore and John R. Battista of Louisiana State University
have suggested the radioresistance of D. radiodurans is simply a side effect of a mechanism for dealing with prolonged cellular desiccation
(dryness). To support this hypothesis, they performed an experiment in which they demonstrated that mutant strains of D. radiodurans which are highly susceptible to damage from ionizing radiation
are also highly susceptible to damage from prolonged desiccation, while the wild-type strain is resistant to both. In addition to DNA repair, D. radiodurans use LEA proteins (Late Embryogenesis Abundant proteins
) expression to protect against desiccation.
Scanning electron microscopy analysis has shown that DNA in D. radiodurans is organized into tightly packed toroid
s, which may facilitate DNA repair.
A team of Croatian and French researchers led by Miroslav Radman
have bombarded D. radiodurans to study the mechanism of DNA repair. At least two copies of the genome, with random DNA breaks, can form DNA fragments through annealing. Partially overlapping fragments are then used for synthesis of homologous regions through a moving D-loop
that can continue extension until they find complementary partner strands. In the final step, there is crossover
by means of RecA
-dependent homologous recombination
.
Michael Daly has suggested the bacterium uses manganese
complexes as antioxidant
s to protect itself against radiation damage. In 2007 his team showed that high intracellular levels of manganese(II) in D. radiodurans protect proteins from being oxidized by radiation, and proposed the idea that "protein, rather than DNA, is the principal target of the biological action of [ionizing radiation] in sensitive bacteria, and extreme resistance in Mn-accumulating bacteria is based on protein protection".
A team of Russian and American scientists proposed that the radioresistance of D. radiodurans had a Martian
origin. Evolution of the microorganism could have taken place on the Martian surface until it was delivered to Earth on a meteorite
. However, apart from its resistance to radiation, Deinococcus is genetically and biochemically very similar to other terrestrial life forms, arguing against an extraterrestrial origin.
In 2009, nitric oxide
was reported to play an important role in the bacteria's recovery from radiation exposure: the gas is required for division and proliferation after DNA damage has been repaired. A gene was described that increases nitric oxide production after UV radiation, and in the absence of this gene, the bacteria were still able to repair DNA damage, but would not grow.
for use in bioremediation
to consume and digest solvent
s and heavy metals
, even in a highly radioactive site. For example, the bacterial mercuric reductase
gene
has been cloned from Escherichia coli
into Deinococcus to detoxify the ion
ic mercury
residue frequently found in radioactive waste
generated from nuclear weapon
s manufacture. Those researchers developed a strain
of Deinococcus that could detoxify both mercury and toluene
in mixed radioactive wastes.
The Craig Venter Institute
has used a system derived from the rapid DNA repair mechanisms of D. radiodurans to assemble synthetic DNA fragments into chromosomes,(this is incorrect, we tried for a long time to reproduce an invitro version of the Deinococcus DNA repair system without success. We used the yeast recombination system for the final stage assembly of the synthetic genomes) with the ultimate goal of producing a synthetic organism they call Mycoplasma laboratorium
.
In 2003, U.S. scientists demonstrated D. radiodurans could be used as a means of information storage that might survive a nuclear catastrophe. They translated the song It's a Small World into a series of DNA segments 150 base pair
s long, inserted these into the bacteria, and were able to retrieve them without errors 100 bacterial generations later.
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...
bacterium, one of the most radioresistant organisms known. It can survive cold, dehydration, vacuum, and acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
, and is therefore known as a polyextremophile
Polyextremophile
A polyextremophile is an organism which combines several extremophilic features. For example, a polyextremophile living at the summit of a mountain in the Atacama Desert might be a radioresistant xerophile, a psychrophile, and an oligotroph...
and has been listed as the world's toughest bacterium in The Guinness Book Of World Records
Guinness World Records
Guinness World Records, known until 2000 as The Guinness Book of Records , is a reference book published annually, containing a collection of world records, both human achievements and the extremes of the natural world...
.
Name and classification
The name Deinococcus radiodurans derives from the Ancient GreekAncient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
δεινός (deinos) and kokkos meaning "terrible grain" and the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
radius and durare, meaning "radiation surviving". The species was formerly called Micrococcus radiodurans. As a consequence of its hardiness, it has been nicknamed Conan the Bacterium
Conan the Barbarian
Conan the Barbarian is a fictional sword and sorcery hero that originated in pulp fiction magazines and has since been adapted to books, comics, several films , television programs, video games, roleplaying games and other media...
.
Initially, it was placed in the genus Micrococcus
Micrococcus
Micrococcus is a genus of bacteria in the Micrococcaceae family. Micrococcus occurs in a wide range of environments, including water, dust, and soil. Micrococci have Gram-positive spherical cells ranging from about 0.5 to 3 micrometers in diameter and are typically appear in tetrads...
. After evaluation of ribosomal
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
sequences and other evidence, it was placed in its own genus Deinococcus
Deinococcus
The Deinococcus is the one genus of three of the Deinococcales group from the Deinococcus-Thermus phylum highly resistant to environmental hazards.There are 47 species of Deinococcus described according to NCBI on 25 august 2011 :...
, which is closely related to the genus Thermus of heat-resistant bacteria; the group consisting of the two is accordingly known as Deinococcus-Thermus
Deinococcus-Thermus
The Deinococcus-Thermus are a small group of bacteria composed of cocci highly resistant to environmental hazards.There are two main groups.* The Deinococcales include two families, with three genera, Deinococcus and Truepera, the former with several species that are resistant to radiation; they...
.
Deinococcus is the only genus in the order Deinococcales. D. radiodurans is the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
of this genus, and the best studied member. All known members of the genus are radioresistant: D. proteolyticus, D. radiopugnans, D. radiophilus, D. grandis, D. indicus, D. frigens, D. saxicola, D. marmoris, D. deserti, D. geothermalis and D. murrayi; the latter two are also thermophilic
Thermophile
A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C . Many thermophiles are archaea...
.
History
D. radiodurans was discovered in 1956 by Arthur W. Anderson at the Oregon Agricultural Experiment Station in Corvallis, OregonCorvallis, Oregon
Corvallis is a city located in central western Oregon, United States. It is the county seat of Benton County and the principal city of the Corvallis, Oregon Metropolitan Statistical Area, which encompasses all of Benton County. As of the 2010 United States Census, the population was 54,462....
. Experiments were being performed to determine if canned food could be sterilized using high doses of gamma radiation. A tin of meat was exposed to a dose of radiation that was thought to kill all known forms of life, but the meat subsequently spoiled, and D. radiodurans was isolated.
The complete DNA sequence of D. radiodurans was published in 1999 by TIGR
The Institute for Genomic Research
The Institute for Genomic Research was a non-profit genomics research institute founded in 1992 by Craig Venter in Rockville, Maryland, United States. It is now a part of the J. Craig Venter Institute.-History:...
. A detailed annotation and analysis of the genome appeared in 2001. The sequenced strain was ATCC BAA-816.
Deinococcus radiodurans has a unique quality in which it can repair both single- and double-stranded DNA. When a mutation is apparent to the cell, it brings it into a compartmental ring-like structure, where the DNA is repaired and then is able to fuse the nucleoids from the outside of the compartment with the damaged DNA.
Description
D. radiodurans is a rather large, spherical bacterium, with a diameter of 1.5 to 3.5 µmMicrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
. Four cells normally stick together, forming a tetrad. The bacteria are easily cultured and do not appear to cause disease. Colonies are smooth, convex, and pink to red in color. The cells stain Gram positive, although its cell envelope is unusual and is reminiscent of the cell walls of Gram negative bacteria.
D. radiodurans does not form endospore
Endospore
An endospore is a dormant, tough, and temporarily non-reproductive structure produced by certain bacteria from the Firmicute phylum. The name "endospore" is suggestive of a spore or seed-like form , but it is not a true spore . It is a stripped-down, dormant form to which the bacterium can reduce...
s and is nonmotile. It is an obligate aerobic
Aerobic organism
An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...
chemoorganoheterotroph
Chemoorganoheterotrophy
A chemoorganoheterotrophic organism is one that requires organic substrates to get its carbon for growth and development, and that produces its energy from oxido-reduction of an organic compound. This group of organisms may be further subdivided according to what kind of organic substrate and...
, i.e., it uses oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
to derive energy from organic compounds in its environment. It is often found in habitats rich in organic materials, such as soil, feces, meat, or sewage, but has also been isolated from dried foods, room dust, medical instruments and textiles.
It is extremely resistant to ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
, ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light, desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
, and oxidizing and electrophilic
Electrophile
In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...
agents.
Its genome consists of two circular chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s, one 2.65 million base pairs long and the other 412,000 base pairs long, as well as a megaplasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
of 177,000 base pairs and a plasmid
Plasmid
In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...
of 46,000 base pairs. It has about 3,195 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s. In its stationary phase, each bacterial cell contains four copies of this genome; when rapidly multiplying, each bacterium contains 8-10 copies of the genome.
Ionizing radiation resistance
D. radiodurans is capable of withstanding an acute dose of 5,000 GyGray (unit)
The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
with almost no loss of viability, and an acute dose of 15,000 Gy with 37% viability. A dose of 5,000 Gy is estimated to introduce several hundred double-strand breaks (DSBs) into the organism's DNA (~0.005 DSB/Gy/Mbp (haploid genome)). For comparison, a chest X-ray or Apollo mission involves about 1 mGy, 5 Gy can kill a human, 200-800 Gy will kill E. coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
, and over 4,000 Gy will kill the radiation-resistant tardigrade
Tardigrade
Tardigrades form the phylum Tardigrada, part of the superphylum Ecdysozoa. They are microscopic, water-dwelling, segmented animals with eight legs. Tardigrades were first described by Johann August Ephraim Goeze in 1773...
.
Several bacteria of comparable radioresistance are now known, including some species of the genus Chroococcidiopsis
Chroococcidiopsis
Chroococcidiopsis is one of the most primitive cyanobacteria, blue-green algae, known. It is a photosynthetic, coccoidal bacteria and is known for its ability to survive harsh environmental conditions, including both high and low temperatures, high salt content, ionizing radiation, and high salinity...
(phylum cyanobacteria) and some species of Rubrobacter
Rubrobacter
Rubrobacter is a genus of Actinobacteria, given its own subclass . It is radiotolerant and may rival Deinococcus radiodurans in this regard....
(phylum actinobacteria
Actinobacteria
Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria....
); among the archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
, the species Thermococcus
Thermococcus
In taxonomy, Thermococcus is a genus of extreme thermophiles in the family the Thermococcaceae.They consist of gram-negative spheres that move with flagella. They are organothrophic anaerobes, growing in temperatures above 70°C...
gammatolerans shows comparable radioresistance. Deinocuccus radiodurans also has a unique ability to repair damaged DNA. It isolates the damaged segments in a controlled area and repairs it. This bacteria can also repair many small fragments from an entire chromosome.
Ionizing radiation resistance mechanisms
Deinococcus accomplishes its resistance to radiation by having multiple copies of its genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
and rapid DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
mechanisms. It usually repairs breaks in its chromosomes within 12–24 hours through a 2-step process. First, D. radiodurans reconnects some chromosome fragments through a process called single-stranded annealing. In the second step, a protein mends double-strand breaks through homologous recombination
Homologous recombination
Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks...
. This process does not introduce any more mutations than a normal round of replication would.
A persistent question regarding D. radiodurans is how such a high degree of radioresistance could evolve. Natural background radiation
Background radiation
Background radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....
levels are very low—in most places, on the order of 0.4 mGy per year, and the highest known background radiation, near Ramsar, Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
is only 260 mGy per year. With naturally-occurring background radiation levels so low, organisms evolving mechanisms specifically to ward off the effects of high radiation are unlikely.
Valerie Mattimore and John R. Battista of Louisiana State University
Louisiana State University
Louisiana State University and Agricultural and Mechanical College, most often referred to as Louisiana State University, or LSU, is a public coeducational university located in Baton Rouge, Louisiana. The University was founded in 1853 in what is now known as Pineville, Louisiana, under the name...
have suggested the radioresistance of D. radiodurans is simply a side effect of a mechanism for dealing with prolonged cellular desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
(dryness). To support this hypothesis, they performed an experiment in which they demonstrated that mutant strains of D. radiodurans which are highly susceptible to damage from ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
are also highly susceptible to damage from prolonged desiccation, while the wild-type strain is resistant to both. In addition to DNA repair, D. radiodurans use LEA proteins (Late Embryogenesis Abundant proteins
Late Embryogenesis Abundant proteins
Late Embryogenesis Abundant proteins are proteins in animals and plants that protect other proteins from aggregation from desiccation or osmotic stresses associated with low temperature. LEA proteins were initially discovered accumulating late in embryogenesis of cotton seeds...
) expression to protect against desiccation.
Scanning electron microscopy analysis has shown that DNA in D. radiodurans is organized into tightly packed toroid
Toroid
Toroid may refer to*Toroid , a doughnut-like solid whose surface is a torus.*Toroidal inductors and transformers which have wire windings on circular ring shaped magnetic cores.*Vortex ring, a toroidal flow in fluid mechanics....
s, which may facilitate DNA repair.
A team of Croatian and French researchers led by Miroslav Radman
Miroslav Radman
Miroslav Radman is a prominent Croatian biologist and a member of the French Academy of Sciences. Radman's specialty is DNA repair; in 1974 he discovered the SOS response...
have bombarded D. radiodurans to study the mechanism of DNA repair. At least two copies of the genome, with random DNA breaks, can form DNA fragments through annealing. Partially overlapping fragments are then used for synthesis of homologous regions through a moving D-loop
D-loop
In molecular biology, a displacement loop or D-loop is a DNA structure where the two strands of a double-stranded DNA molecule are separated for a stretch and held apart by a third strand of DNA. The third strand has a base sequence which is complementary to one of the main strands and pairs with...
that can continue extension until they find complementary partner strands. In the final step, there is crossover
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...
by means of RecA
RecA
RecA is a 38 kilodalton Escherichia coli protein essential for the repair and maintenance of DNA. RecA has a structural and functional homolog in every species in which it has been seriously sought and serves as an archetype for this class of homologous DNA repair proteins...
-dependent homologous recombination
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...
.
Michael Daly has suggested the bacterium uses manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
complexes as antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
s to protect itself against radiation damage. In 2007 his team showed that high intracellular levels of manganese(II) in D. radiodurans protect proteins from being oxidized by radiation, and proposed the idea that "protein, rather than DNA, is the principal target of the biological action of [ionizing radiation] in sensitive bacteria, and extreme resistance in Mn-accumulating bacteria is based on protein protection".
A team of Russian and American scientists proposed that the radioresistance of D. radiodurans had a Martian
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
origin. Evolution of the microorganism could have taken place on the Martian surface until it was delivered to Earth on a meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
. However, apart from its resistance to radiation, Deinococcus is genetically and biochemically very similar to other terrestrial life forms, arguing against an extraterrestrial origin.
In 2009, 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...
was reported to play an important role in the bacteria's recovery from radiation exposure: the gas is required for division and proliferation after DNA damage has been repaired. A gene was described that increases nitric oxide production after UV radiation, and in the absence of this gene, the bacteria were still able to repair DNA damage, but would not grow.
Applications
Deinococcus has been genetically engineeredGenetic engineering
Genetic engineering, also called genetic modification, is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest...
for use 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...
to consume and digest solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s and heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...
, even in a highly radioactive site. For example, the bacterial mercuric reductase
Mercury(II) reductase
In enzymology, a mercury reductase is an enzyme that catalyzes the chemical reactionThe 3 substrates of this enzyme are Hg, NADP+, and H+, whereas its two products are Hg2+ and NADPH....
gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
has been cloned from Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
into Deinococcus to detoxify the ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
ic mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
residue frequently found in radioactive waste
Radioactive waste
Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...
generated from nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s manufacture. Those researchers developed a strain
Strain (biology)
In biology, a strain is a low-level taxonomic rank used in three related ways.-Microbiology and virology:A strain is a genetic variant or subtype of a micro-organism . For example, a "flu strain" is a certain biological form of the influenza or "flu" virus...
of Deinococcus that could detoxify both mercury and toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
in mixed radioactive wastes.
The Craig Venter Institute
J. Craig Venter Institute
The J. Craig Venter Institute is a non-profit genomics research institute founded by J. Craig Venter, Ph.D. in October 2006. The Institute was the result of consolidating four organizations: the Center for the Advancement of Genomics, The Institute for Genomic Research, the Institute for...
has used a system derived from the rapid DNA repair mechanisms of D. radiodurans to assemble synthetic DNA fragments into chromosomes,(this is incorrect, we tried for a long time to reproduce an invitro version of the Deinococcus DNA repair system without success. We used the yeast recombination system for the final stage assembly of the synthetic genomes) with the ultimate goal of producing a synthetic organism they call Mycoplasma laboratorium
Mycoplasma laboratorium
Mycoplasma laboratorium is a planned partially synthetic species of bacterium derived from the genome of Mycoplasma genitalium. This effort in synthetic biology is being undertaken at the J. Craig Venter Institute by a team of approximately 20 scientists headed by Nobel laureate Hamilton Smith, and...
.
In 2003, U.S. scientists demonstrated D. radiodurans could be used as a means of information storage that might survive a nuclear catastrophe. They translated the song It's a Small World into a series of DNA segments 150 base pair
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
s long, inserted these into the bacteria, and were able to retrieve them without errors 100 bacterial generations later.
See also
- Thermococcus gammatoleransThermococcus gammatoleransThermococcus gammatolerans is an archaea extremophile and the most radiation resistant known organism.Discovered in 2003 in a submarine hydrothermal vent in the Guaymas Basin about 2,000 meters deep off the coast of California...
- RubrobacterRubrobacterRubrobacter is a genus of Actinobacteria, given its own subclass . It is radiotolerant and may rival Deinococcus radiodurans in this regard....
- DNA repairDNA repairDNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
- Rejuvenation (aging)Rejuvenation (aging)Rejuvenation is the hypothetical reversal of the aging process.Rejuvenation is distinct from life extension. Life extension strategies often study the causes of aging and try to oppose those causes in order to slow aging...
- Radiotrophic fungusRadiotrophic fungusRadiotrophic fungi are fungi which appear to use the pigment melanin to convert gamma radiation into chemical energy for growth. This proposed mechanism may be similar to anabolic pathways for the synthesis of reduced organic carbon in phototrophic organisms, which capture photons from visible...
- Background radiationBackground radiationBackground radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....
- List of sequenced bacterial genomes
External links
- Microbe of the Week page from the University of Missouri-Rolla
- Taxonomy of Deinococcus
- Microbial Biorealm entry from Kenyon College
- Downloadable D. radiodurans publications
- Deinococcus radiodurans Genome Page
- Meet Conan the Bacterium -- Humble microbe could become -- The Accidental (Space) Tourist
- Deinococcus-Thermus: Adaptations to "nearly out of this world" environments -- Tree of Life project