Deinococcus Radiodurans
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''Deinococcus radiodurans'' is a
bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
, an
extremophile An extremophile () is an organism that is able to live (or in some cases thrive) in extreme environments, i.e., environments with conditions approaching or stretching the limits of what known life can adapt to, such as extreme temperature, press ...
and one of the most radiation-resistant organisms known. It can survive cold,
dehydration In physiology, dehydration is a lack of total body water that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of water. Mild deh ...
,
vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...
, and
acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
, and therefore is known as a polyextremophile. ''The Guinness Book Of World Records'' listed it in January 1998 as the world's most radiation-resistant bacterium or lifeform. Several bacteria of comparable radioresistance are known, including some species of the genus '' Chroococcidiopsis'' (phylum
cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
) and some species of '' Rubrobacter'' (phylum Actinomycetota); among the
archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
, the species '' Thermococcus gammatolerans'' shows comparable radioresistance.


Name and classification

The name ''Deinococcus radiodurans'' derives from the
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
δεινός () and κόκκος () meaning "terrible grain/berry" and the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
and , meaning "radiation-surviving". The species was formerly called ''Micrococcus radiodurans''. As a consequence of its hardiness, it has been nicknamed “Conan the Bacterium”, in reference to
Conan the Barbarian Conan the Barbarian (also known as Conan the Cimmerian) is a fictional sword and sorcery hero created by American author Robert E. Howard (1906–1936) and who debuted in 1932 and went on to appear in a series of fantasy stories published in ''We ...
. Initially, it was placed in the genus '' Micrococcus''. After evaluation of ribosomal
RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
sequences and other evidence, it was placed in its own genus '' Deinococcus'', which is closely related to the genus '' Thermus''. ''Deinococcus'' is one genus of three in the order ''Deinococcales''. ''D. radiodurans'' is the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
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 A thermophile is a type of extremophile that thrives at relatively high temperatures, between . Many thermophiles are archaea, though some of them are bacteria and fungi. Thermophilic eubacteria are suggested to have been among the earliest bact ...
.


History

''D. radiodurans'' was discovered in 1956 by Arthur Anderson at the Oregon Agricultural Experiment Station in Corvallis, Oregon. Experiments were being performed to determine whether 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 A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...
of ''D. radiodurans'' was published in 1999 by The Institute for Genomic Research. A detailed annotation and analysis of the genome appeared in 2001. The genome is found in four parts: two chromosomes sized 2.65 Mbp and 412 kbp, one megaplasmid of 177 kbp, and one regular-sized plasmid of 46 kbp. The sequenced strain was ATCC BAA-816. In August 2020, scientists reported that
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
from Earth, particularly ''Deinococcus radiodurans'' bacteria, were found to survive for three years in outer space, based on studies conducted on the
International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...
(ISS). These findings support the notion of panspermia, the hypothesis that
life Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...
exists throughout the
Universe The universe is all of space and time and their contents. It comprises all of existence, any fundamental interaction, physical process and physical constant, and therefore all forms of matter and energy, and the structures they form, from s ...
, distributed in various ways, including space dust,
meteoroid A meteoroid ( ) is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than ''asteroids'', ranging in size from grains to objects up to wide. Objects smaller than meteoroids are classifie ...
s,
asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...
s,
comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
s, planetoids, or contaminated
spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...
.


Description

''D. radiodurans'' is a rather large, spherical bacterium, with a diameter of 1.5 to 3.5 μm. Four cells normally stick together, forming a tetrad. The bacteria are easily cultured and do not appear to cause disease. Under controlled growth conditions, cells of dimer, tetramer, and even multimer morphologies can be obtained. 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. ''Deinococcus radiodurans'' does not form
endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., not ...
s and is nonmotile. It is an obligate aerobic chemoorganoheterotroph, i.e., it uses
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
to derive energy from organic compounds in its environment. It is often found in habitats rich in organic materials, such as sewage, meat, feces, or, soil, but has also been isolated from medical instruments, room dust, textiles, and dried foods. It is extremely resistant to
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
,
ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...
light,
desiccation Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...
, and oxidizing and electrophilic agents. PCR assays and Fluorescent in Situ Hybridization (FISH) techniques can be used to test for ''D. radiodurans'' in nature. Its genome consists of two circular
chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...
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 A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria and ...
of 46,000 base pairs. It has approximately 3,195
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
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

''Deinococcus radiodurans'' is capable of withstanding an acute dose of 5,000  grays (Gy), or 500,000 rad, of
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
with almost no loss of viability, and an acute dose of 12,000 grays with 10% survivability. A dose of 5,000 Gy is estimated to introduce several dozens double-strand breaks (DSBs) into the organism's DNA: given the estimated rate of 0.005 DSB/Gy/Mbp, the approximately 3.2 Mbp bacterial genome should have received 80 DSBs if it was haploid. 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 more than 4,000 Gy will kill the radiation-resistant
tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them . In 1776, th ...
.


Mechanisms of ionizing-radiation resistance


DNA structure

''Deinococcus'' accomplishes its resistance to radiation by having multiple copies of its
genome 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 genes, other functional regions of the genome such as ...
.
Scanning electron microscopy A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...
analysis has shown that DNA in ''D. radiodurans'' is organized into tightly packed toroids, which may facilitate DNA repair.


DNA repair

''Deinococcus radiodurans'' has a unique quality in which it can repair both single- and double-stranded DNA. When damage is apparent to the cell, it brings the damaged DNA 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. ''Deinococcus'' usually repairs breaks in its chromosomes within 12–24 hours by a 2-step process. * First, ''D. radiodurans'' reconnects some chromosome fragments by a process called single-stranded annealing. This is facilitated having multiple copies of the genome, and as few as two copies can perform annealing. Partially overlapping fragments are then used for synthesis of homologous regions through a moving D-loop that can continue extension until the fragments find complementary partner strands. * In the second step, multiple proteins mend double-strand breaks through
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...
. RecA performs
chromosomal crossover Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' sister chromatids, non-sister chromatids that results in recombinant chromosomes. It is one of the fina ...
across multiple copies of the (possibly partial) genome to generate complete copies. ''Deinococcus radiodurans'' is capable of genetic transformation, a process by which DNA derived from one cell can be taken up by another cell and integrated into the recipient genome by homologous recombination. This may help if the DNA in a single cell is insufficient for repair into a complete chromosome. Natural genetic transformation under stressful conditions in ''D. radiodurans'' is associated with repair of DNA damage. When DNA damages (e.g. pyrimidine dimers) are introduced into donor DNA by UV irradiation, the recipient cells efficiently repair the damages in the transforming DNA, as they do in cellular DNA, when the cells themselves are irradiated.


Additional protective mechanisms

Michael Daly has suggested the bacterium uses
manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...
complexes as
antioxidant Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
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 they proposed the idea that "protein, rather than DNA, is the principal target of the biological action of onizing radiationin sensitive bacteria, and extreme resistance in Mn-accumulating bacteria is based on protein protection". In 2016, Massimiliano Peana ''et al''. reported a spectroscopic study through NMR, EPR, and ESI-MS techniques on the Mn(II) interaction with two peptides, DP1 (DEHGTAVMLK) and DP2 (THMVLAKGED), whose amino acid composition was selected to include the majority of the most prevalent amino acids present in a Deinococcus radiodurans bacterium cell-free extract that contains components capable of conferring extreme resistance to ionizing radiation. In 2018, M. Peana and C. Chasapis reported by a combined approach of bioinformatic strategies based on structural data and annotation, the Mn(II)-binding proteins encoded by the genome of DR and proposed a model for Manganese interaction with DR proteome network involved in ROS response and defense. In 2009,
nitric oxide Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...
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. A few more mechanisms (LEA and SDBC) are described in the following section.


Evolution of ionizing-radiation resistance

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 Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
, 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. In the distant geological past, higher background radiation existed both due to more primordial radionuclides not yet having decayed and due to effects of things like the natural nuclear fission reactors at Oklo, Gabon, which were active some 1.7 billion years ago. However, even if adaptations to such conditions ''did'' evolve during that time,
genetic drift Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...
would almost certainly have eliminated them if they provided no (other) evolutionary benefit. A team of Russian and American scientists proposed that the radioresistance of ''D. radiodurans'' had a Martian origin. They suggested that evolution of the microorganism could have taken place on the Martian surface until it was delivered to Earth on a
meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...
. However, apart from its resistance to radiation, ''Deinococcus'' is genetically and biochemically very similar to other terrestrial life forms, arguing against a unique extraterrestrial origin. Valerie Mattimore of
Louisiana State University Louisiana State University and Agricultural and Mechanical College, commonly referred to as Louisiana State University (LSU), is an American Public university, public Land-grant university, land-grant research university in Baton Rouge, Louis ...
has suggested the radioresistance of ''D. radiodurans'' is simply a side effect of a mechanism for dealing with prolonged cellular
desiccation Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...
(dryness). To support this hypothesis, she performed an experiment in which she demonstrated that mutant strains of ''D. radiodurans'' that are highly susceptible to damage from
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
are also highly susceptible to damage from prolonged desiccation, while the wild-type strain is resistant to both. It was also shown that desiccation induces double-stranded DNA breaks with patterns similar to extreme ionizing radiation. In addition to DNA repair, ''D. radiodurans'' use LEA proteins ( Late Embryogenesis Abundant proteins) expression to protect against desiccation. In this context, also the robust cell envelope of ''D. radiodurans'' through its main protein complex, the S-layer Deinoxanthin Binding Complex (SDBC), strongly contributes to both physiological functions and its extreme radioresistance. In fact, this protein complex acts as a shield against electromagnetic stress, as in the case of ionizing radiation exposure, but also stabilizes the cell envelope against possible consequent high temperatures and desiccation.


Applications

''Deinococcus radiodurans'' has been shown to have a great potential to be used in different fields of investigation. Not only has ''D. radiodurans'' been genetically modified for
bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, wate ...
applications, but also it has been discovered that it could perform a major role in biomedical research and in
nanotechnology Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...
.
Bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, wate ...
refers to any process that uses microorganisms, fungi, plants, or the enzymes derived from them, to return an environment altered by contaminants to its natural condition. Large areas of soils, sediments, and groundwater are contaminated with radionuclides, heavy metals, and toxic solvents. There are microorganisms that are able to decontaminate soils with heavy metals by immobilizing them, but in the case of nuclear waste,
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
limits the amount of microorganisms that can be useful. In this sense, ''D. radiodurans'', due to its characteristics, can be used for the treatment of
nuclear energy Nuclear energy may refer to: *Nuclear power, the use of sustained nuclear fission or nuclear fusion to generate heat and electricity *Nuclear binding energy, the energy needed to fuse or split a nucleus of an atom *Nuclear potential energy, the pot ...
waste. ''Deinococcus radiodurans'' has been genetically engineered to consume and digest solvents and heavy metals in these radioactive environments. The mercuric reductase
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
has been cloned from ''
Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...
'' into ''Deinococcus'' to detoxify the ionic mercury residue frequently found in
radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...
generated from
nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
s manufacture. Those researchers developed a strain of ''Deinococcus'' that could detoxify both mercury and
toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...
in mixed radioactive wastes. Moreover, a gene encoding a non-specific acid
phosphatase In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid Ester, monoester into a phosphate ion and an Alcohol (chemistry), alcohol. Because a phosphatase enzyme catalysis, catalyzes the hydrolysis of its Substrate ...
from '' Salmonella enterica'', serovar Typhi, and the alkaline
phosphatase In biochemistry, a phosphatase is an enzyme that uses water to cleave a phosphoric acid Ester, monoester into a phosphate ion and an Alcohol (chemistry), alcohol. Because a phosphatase enzyme catalysis, catalyzes the hydrolysis of its Substrate ...
gene from '' Sphingomonas'' have been introduced in strains of ''D. radiodurans'' for the bioprecipitation of uranium in acid and alkaline solutions, respectively. In the biomedical field, ''Deinococcus radiodurans'' could be used as a model to study the processes that lead to
aging Ageing (or aging in American English) is the process of becoming Old age, older until death. The term refers mainly to humans, many other animals, and fungi; whereas for example, bacteria, perennial plants and some simple animals are potentiall ...
and
cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
. The main causes of these physiological changes are related to the damage in
DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
,
RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...
, and
proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...
resulting from
oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...
, the weakening of antioxidant defense, and the inability of repair mechanisms to deal with the damage originated by reactive oxygen species, also known as ROS. To this extent, ''D. radiodurans'' mechanisms of protection against oxidative damage and of DNA reparation could be the starting points in research aimed to develop medical procedures to prevent
aging Ageing (or aging in American English) is the process of becoming Old age, older until death. The term refers mainly to humans, many other animals, and fungi; whereas for example, bacteria, perennial plants and some simple animals are potentiall ...
and
cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
. Some lines of investigation are focused on the application of ''D. radiodurans'' antioxidant systems in human cells to prevent ROS damaging and the study of the development of resistance to radiation in tumoral cells. A nanotechnological application of ''D. radiodurans'' in the synthesis of
silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
and
gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
nanoparticles has also been described. Whereas chemical and physical methods to produce these nanoparticles are expensive and generate a huge amount of pollutants, biosynthetic processes represent an ecofriendly and cheaper alternative. The importance of these nanoparticles relies on their medical applications as they have been demonstrated to exhibit activity against pathogenic bacteria, antifouling effects, and
cytotoxicity Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are toxic metals, toxic chemicals, microbe neurotoxins, radiation particles and even specific neurotransmitters when the system is out of balance. Also some types of d ...
to tumoral cells. Moreover, there are other uncommon applications of ''Deinococcus radiodurans''. 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, 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 It's a Small World (stylized in all lowercase and in quotations or with exclamation mark) is an Old Mill boat ride located in the Fantasyland area at various Disney theme parks around the world. Versions of the ride are installed at Disney ...
" into a series of DNA segments 150
base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
s long, inserted these into the bacteria, and were able to retrieve them without errors 100 bacterial generations later.


Clues for future search of extremophile microbial life on Mars

When cultured and exposed to ionizing radiations in liquid media, ''Deinococcus radiodurans'' could survive up to 25 kGy. Horne et al. (2022) have studied the effects of desiccation and freezing on the microbial survivability to ionizing radiations considering the feasibility studies to return Martian subsurface soil samples for microbial characterization and for determining the most favorable landing sites of a future robotic exploration mission. They found that the desiccated and frozen cells could resist to a 5.6 higher radiation dose: up to 140 kGy. They calculated that this could correspond to a theoretical survival time of 280 million years at a depth of 33 feet (10 m) below the Mars surface. However, this time scale is too short to allow microbial survival at a depth accessible to a rover equipped with a drilling system below the Martian surface when compared to the moment when liquid water disappeared from the Martian surface (2 – 2.5 billion years ago). Nevertheless, Horne et al. (2022) consider the hypothesis that meteorite impacts could have dispersed Martian soil and heated locally the subsurface during the geological history of Mars, heating sporadically from time to time the local environment, melting the frozen ice and giving perhaps a chance to a hypothetical distant Martian
extremophile An extremophile () is an organism that is able to live (or in some cases thrive) in extreme environments, i.e., environments with conditions approaching or stretching the limits of what known life can adapt to, such as extreme temperature, press ...
resembling its terrestrial cousin ''Deinococcus radiodurans'' to grow again for short moment before to rapidly become again frozen and dormant for millions of years. So, for returning subsurface soil samples from Mars for microbial characterization with a potentially ''"successful"'' mission like the European Rosalind Franklin rover, it would be necessary to target a relatively young
impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...
to increase the chances of discovering dormant extremophile micro-organisms surviving in the dry and frozen Martian subsurface environment relatively protected from the lethal ionizing radiations.


See also

* Extremophiles * List of sequenced bacterial genomes * Pyrococcus * Radiosynthesis (metabolism) * Radiotrophic fungus * '' Thermococcus gammatolerans''


References


External links

* *
Microbe of the Week page from the University of Missouri-Rolla

Taxonomy of Deinococcus

''Deinococcus radiodurans'' Genome Page


* ttp://tolweb.org/treehouses/?treehouse_id=4726 Deinococcus-Thermus: Adaptations to "nearly out of this world" environments – Tree of Life project
Type strain of ''Deinococcus radiodurans'' at Bac''Dive'' – the Bacterial Diversity Metadatabase

KEGG Genome: ''Deinococcus radiodurans''
{{Authority control Polyextremophiles Radiodurants Deinococcales DNA repair Bacteria described in 1981