Deinococcus radiodurans

Deinococcus radiodurans is a bacterium Polyextrémophile and known organization more radiorésistant in the world. This bacterium has an impressive resistance, in particular with UV, the ionizing radiations, the Hydrogen peroxide, the Vide, the acid , the extreme temperatures, the drying, the cold and the Famine. This capacity of resistance is due to its particular cellular structure and its very sophisticated system of repair of the DNA, which even enables him to be able “ressusciter” a few hours after its death.

Because of its extraordinary resistance, it was affublée of nicknames such as “Conan the bacterium” or “the bacterium most resistant to the world”. Some put forth the assumption that it can be a question of a bacterium Extra-terrestre which would have been brought on Ground by a Météorite.

Discovered and Historical

Deinococcus radiodurans was discovered for the premère time in 1956 by A.W. Anderson, of the Agricultural Oregon Experiment Station , with Corvallis in the Oregon, during experiments carried out to so determine cans could be sterilized by great amounts of Gamma rays. A preserve meat box was exposed to an amount of radiation supposed to kill any known form of life, but with the general surprise the process of decomposition does not stop.

A bacterium is quickly isolated and is quickly studied under all the seams. It proves to be resistant to a great number of extreme situations, like the exposure to the chemicals genotoxic, the damage of oxidation, the ionizing rays and ultra-violets, and dehydration.

Initially called Deinobacter radiodurans , the bacterium was then famous Deinococcus radiodurans .

Medium of life

Since the episode of limps of preserve, it was found a little everywhere in the world, its qualities returning it ubiquist. He as well saw in zones rich in food like the grounds or the animal feces as in zones very low in nutritive substances, as the surface of certain disaggregated granites of the valleys of the Antarctic or the surgical instruments irradiated.

Resistances

Strength to the radioactivity

No living organism in the world with the strength of Deinococcus radiodurans to the radioactivity. It resists radiation levels going up to five million rads, that is to say 5000 times the amount mortal of 1000 rads (10 Gy) likely to kill a man. Exposed to 1,5 million rads, Deinococcus radiodurans repairs its DNA in only a few hours and without loss of viability. It supports to 150 breaks of the double bit by chromosome without mutagen effect whereas Escherichia coli supports of them only 2 or 3 maximum and sudden of the noxious changes.

Resistance to UV

Deinococcus radiodurans is also the only known organization which resists the ultraviolet radiations. It can tolerate 10 000 times the amount mortal of radiation UV tolerated by the organizations eucaryotes and 100 times the amount mortal for the majority of the procaryotic organizations.

Genotoxic chemistry

Deinococcus radiodurans resists the acid attacks of baths.

Dehydration

Deinococcus radiodurans resists well complete dehydration or desiccation. Once completely dehydrated, it resists still better the radiations and the extreme temperatures.

Extreme temperatures

A temperature of - 45°C inactive Deinococcus radiodurans but does not damage it.

Mechanisms of defense

Many teams quickly tried to include/understand from which this formidable resistance comes.

The irradiation gamma at strong amounts or a long period of desiccation involve very many breaks double-bits of the genome. However D. radiodurans is able to repair these breaks in a few hours in rich medium.

The genome of D. radiodurans was sequence and analyzed entirely (Makarova and Al , 2001, Microbiol Mol Biol Rev 65: 44). The hereditary luggage of the bacterium is contained in four circular molecules including two chromosomes (of 2.648.615 and 412.340 pairs of bases), a mégaplasmide (177 466 pairs of bases) and a plasmide (45 702 pairs of bases).

The researchers discovered that its extreme resistance was due to the conjugation of varied strategies:

Prevention - cellular damage caused by the free radicals.
Repair - chromosomal breaks thanks to a very complete arsenal.
Expulsion - many waste produced during repair and dangerous for its survival.

Prevention

No protective shell not being able to stop the gamma rays - photons of very high energy - and to prevent them from damaging the chromosomes, Deinococcus radiodurans must undergo the consequences of them.

Cellular extensive damage is caused by the appearance of free oxygen radicals following the dessication or to the exposure to rays UV and gamma. Deinococcus radiodurans is equipped with a whole series of enzymes - catalases and superoxyde dismutases (SOD) - specialized in the destruction of these free radicals and much more sensitive to ionizing radiations than those of other organizations.

Work on mutant bacteria showed that the resistance of these bacteria decreased if these various genes are not expressed any more.

Repair

The first phase consists in gathering in the correct order all the fragments in a linear chain; all the pieces will be used as model to initiate the synthesis of DNA and to lengthen the chain by simple bit. The second genetic phase of recombination consists in reconstituting the circular chromosomes of the cell by “crossing over”. Once the genome restored with identical, the synthesis of proteins is again operational: the cell is alive whereas one could regard it as “clinically dead”.

Expulsion

The repair of the chromosomes generates many waste - even transferred cut out fragments of DNA - dangerous for the bacterium because these damaged pieces can be reincorporated with the genome. Deinococcus radiodurans has a single system of cleaning allowing the transport and the expulsion of nucleotides damaged outside the cell.

Once the household carried out, Deinococcus radiodurans can begin a new cycle of cellular division.

Additional defenses

Deinococcus radiodurans also improves its survival while being able to increase its synthesis in precursors to create new molecules and by providing alternative energy sources.

Genes of chromosome II and mégaplasmide seem to be able to manufacture nitrogenized precursors, implied in the production of proteins, starting from the cells not having succeeded in remaining.

Other genes of chromosome II code molecules suitable for degrade the fatty-acids in acétyl-coenzyme has, a cellular energy source used when the other sources of carbon become exhausted.

Outlines

The capacity of exceptional survival of the bacterium Deinococcus radiodurans in radioactive medium quickly drew the attention of the specialists in charge of management in waste.

An American government agency is studying its aptitudes to on the spot cleanse sites contaminated at the same time by radioactive materials and other pollutants, organics and minerals. Only in the United States, the experts listed 3000 of them, on places of production of weapons or nuclear research centres. The analyzes of these grounds show a rather worrying cocktail, where trichloroethylene and toluene are neighborly with uranium, plutonium and various heavy metals. The technique of the biodépollution functions on a very simple idea. One cultivates bacteria which nourish pollutant concerned, oil to take a known example. One sows then the zone to be decontaminated, and one waits until the microbes transform carbonic gas and water the organic pollutant. One knows a whole series of micro-organisms able to break up various organic pollutants or to fix heavy metals. These microbes cannot however not operate in radioactive medium: the fact of carburizing with trichloroethylene does not protect from radiations. From where interest to study the bacterium insensitive with radiations. Is it able to nourish complex organic compounds? Can it fix the radioactive heavy metals, even elements? According to the first studies, it seems that it is able to break up toluene and certain close products. The followers of the genetic engineering also put themselves at work. Their projects consist in equipping Deinococcus radiodurans with genes known to make the bacteria able to digest pollution. The recombined bacterium would be thus at the same time insensitive with the gamma rays and specialist in depollution. The reverse is also considered: to graft genes of protection against radiation on the licensed street sweepers.

External bonds

expert of the patching up, by Fabrice Demarthon, Source: Are science, vol. 286, pp. 1571-1577
what the terrestrial bacterium Deinococcus radiodurans comes from Mars? , ufologie.net

the genome of D.radiodurans
How " Conan the Bacterium" Survive Lethal Radiation Blasts
Humble microbe could become " The Accidental (Space) Tourist"
Microbe off the Week page from the University off Missouri-Rolla
List off species in genus '' Deinococcus ''
Taxonomy off Deinococcus
Microbial Biorealm entry from Kenyon College
DNA Repair
DNA Ramming and DNA Repair

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