Desulforudis audaxviator
Encyclopedia
Desulforudis audaxviator is a monotypic
bacterium, which lives in depths from 1.5 km to 3 km below the Earth's surface in the groundwater.
It is the only bacterium found in water samples obtained 2.8 km underground in the Mponeng
gold mine in South Africa. Approximately four micrometre
s in length, it has survived for millions of years on chemical food sources that derive from the radioactive decay
of minerals in the surrounding rock, making it one of the few organisms known that does not depend on sunlight for nourishment and the only species known to be alone in its ecosystem
. D. audaxviator has genes for extracting carbon from dissolved carbon dioxide
and for nitrogen fixation
. It may also have acquired genes from a species of archaea
by horizontal gene transfer
.
They have been isolated from Earth's surface for several million years, because analyses of the water that they live in showed that it is very old and has not been diluted by surface water. Because the environment at that depth is so much like the early Earth, it gives a handle on what kind of creatures might have existed before there was an oxygen atmosphere. Billions of years ago, some of the first bacteria on the planet may have thrived in similar conditions. The newly discovered microbes could shed light into the origins of life on Earth.
D. audaxviator is a Gram positive sulfate-reducing bacterium (making it the first complete such genome
). The genome contains an unusual transposon
and possesses many sites of insertion. Its complete intolerance of oxygen suggests long-term isolation. The hydrocarbon
s in that environment do not come from living organisms. The source of the hydrogen needed for their respiration comes from the decomposition of water by radioactive decay
of uranium
, thorium
, and potassium
. The radiation allows for the production of sulphur compounds that these bacteria can use as a high-energy source of food.
D. audaxviator not only survives a complete absence of organic compounds, light, and oxygen, but also temperatures as high as 60°C and a pH
of 9.3. The physiology that enables it to live in these extreme conditions is a tribute to its unusually large genome, consisting of 2157 genes instead of the 1500 of its peers. If conditions become unfavorable for normal life, D. audaxviator is able to encyst
, safeguarding its DNA from heat, extreme pH, and the lack of water.
The name comes from a quotation from Jules Verne
's novel Journey to the Center of the Earth
. The hero, Professor Lidenbrock, finds a secret inscription in Latin that reads: Descende, audax viator, et terrestre centrum attinges (Descend, bold traveller, and you will attain the center of the Earth).
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
bacterium, which lives in depths from 1.5 km to 3 km below the Earth's surface in the groundwater.
It is the only bacterium found in water samples obtained 2.8 km underground in the Mponeng
Mponeng
Mponeng is a gold mine in South Africa's North West Province. It extends over two miles below the surface, and is considered to be one of the deepest and most substantial gold mines in the world. The trip from the surface to the bottom of the mine takes over an hour.6,000 tons of rock are...
gold mine in South Africa. Approximately four micrometre
Micrometre
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...
s in length, it has survived for millions of years on chemical food sources that derive from the radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
of minerals in the surrounding rock, making it one of the few organisms known that does not depend on sunlight for nourishment and the only species known to be alone in its ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
. D. audaxviator has genes for extracting carbon from dissolved carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and for nitrogen fixation
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
. It may also have acquired genes from a species of archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
by horizontal gene transfer
Horizontal gene transfer
Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...
.
They have been isolated from Earth's surface for several million years, because analyses of the water that they live in showed that it is very old and has not been diluted by surface water. Because the environment at that depth is so much like the early Earth, it gives a handle on what kind of creatures might have existed before there was an oxygen atmosphere. Billions of years ago, some of the first bacteria on the planet may have thrived in similar conditions. The newly discovered microbes could shed light into the origins of life on Earth.
D. audaxviator is a Gram positive sulfate-reducing bacterium (making it the first complete such genome
Genome
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....
). The genome contains an unusual transposon
Transposon
Transposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
and possesses many sites of insertion. Its complete intolerance of oxygen suggests long-term isolation. The hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s in that environment do not come from living organisms. The source of the hydrogen needed for their respiration comes from the decomposition of water by radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
, and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
. The radiation allows for the production of sulphur compounds that these bacteria can use as a high-energy source of food.
D. audaxviator not only survives a complete absence of organic compounds, light, and oxygen, but also temperatures as high as 60°C and a pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of 9.3. The physiology that enables it to live in these extreme conditions is a tribute to its unusually large genome, consisting of 2157 genes instead of the 1500 of its peers. If conditions become unfavorable for normal life, D. audaxviator is able to encyst
Microbial cyst
A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed down and...
, safeguarding its DNA from heat, extreme pH, and the lack of water.
The name comes from a quotation from Jules Verne
Jules Verne
Jules Gabriel Verne was a French author who pioneered the science fiction genre. He is best known for his novels Twenty Thousand Leagues Under the Sea , A Journey to the Center of the Earth , and Around the World in Eighty Days...
's novel Journey to the Center of the Earth
Journey to the Center of the Earth
A Journey to the Center of the Earth is a classic 1864 science fiction novel by Jules Verne. The story involves a German professor who believes there are volcanic tubes going toward the center of the Earth...
. The hero, Professor Lidenbrock, finds a secret inscription in Latin that reads: Descende, audax viator, et terrestre centrum attinges (Descend, bold traveller, and you will attain the center of the Earth).
See also
- List of sequenced archeal genomes
- AngloGold AshantiAngloGold AshantiAngloGold Ashanti Limited is a global gold mining company. It was formed in 2004 by the merger of AngloGold and the Ashanti Goldfields Corporation.AngloGold Ashanti Limited is now a global gold producer with 21 operations on four continents...
, operator of the Mponeng gold mine
External links
- Build It Bigger: South Africa's Mponeng Gold Mine, at the Discovery ChannelDiscovery ChannelDiscovery Channel is an American satellite and cable specialty channel , founded by John Hendricks and distributed by Discovery Communications. It is a publicly traded company run by CEO David Zaslav...