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Thursday, 18 November, 1999, 19:17 GMT
Radiation beating bug offers cancer clues
Radiation-damaged DNA can be repaired within hours
Radiation-damaged DNA can be repaired within hours
By BBC News Online Science Editor Dr David Whitehouse

It is a pink bacterium that can survive 1.5 million rads of gamma irradiation, a dose 3,000 times more than would kill a human.

Scientists have now read the entire genetic code of the hardy bacterium and, if they can decipher the remarkable way the microbe protects itself, this may lead to a better understanding of cancer and new ways of clearing up nuclear waste.

The bacterium, called Deinococcus radiodurans, was originally isolated from samples of canned meat that were thought to be sterilised. Colonies of harmless bacteria growing on the spoiled meat turned out to be the radiation-resistant organism.

Tough bug: <I>Deinococcus radiodurans</I> was first found on tainted meat
Tough bug: Deinococcus radiodurans was first found on tainted meat
Since it was found in 1956, it has been detected around the world typically in locations where most other bacteria have died from the extreme conditions. It can live in such extreme environments as the shielding pond of a radioactive caesium source and on the surfaces of Arctic rocks.

Its name, due to its berry shape, means "strange or terrible berry that withstands radiation."

The radiation shreds the bacterium's genes into hundreds of pieces but the organism has a remarkable ability to repair this DNA damage completely in a single day and scientists want to find out how it does it.

The process may provide insights into the mechanism of cellular repair which in turn could lead to a deeper understanding of cancer which is frequently caused by unrepaired DNA damage.

<I>D. radiodurans's</I> DNA fragments hold the key to its self-healing
D. radiodurans's DNA fragments hold the key to its self-healing
If scientists can isolate the genes that give the bacterium its remarkable ability then it may be possible to extract them and engineer them into other organisms.

The first stage towards understanding how it does it is to read its genetic blueprint and this is what scientists from the Institute for Genomic Research (TIGR) have done, reporting in the journal Science.

The bacterium's genome is composed of two circular chromosomes that are about 2.6 million and 400,000 DNA base pairs in length.

The genome is also composed of two smaller circular molecules, a so-called megaplasmid of 177,000 base pairs and a plasmid of 45,000 base pairs.

Other bacteria with multiple chromosomes or megaplasmids are known, but D. radiodurans represents the first completely sequenced bacterium with these features.

Many repair kits

Researchers have discovered that while D. radiodurans contained the usual complement of repair genes found in other radiation-sensitive bacteria, it has an unusually large redundancy of repair functions.

"This is a significant accomplishment," said United States Secretary of Energy Bill Richardson who believes the bacterium could be used to clear up nuclear waste.

"Besides the insights into the way cells work, this new research may help provide a new, safe and inexpensive tool for some of the nation's most difficult clean-up challenges."

"We anticipate a terrific boost for industrial and environmental microbiology," said TIGR President Claire Fraser.

"Publication of the Deinococcus sequence will foster more research into cellular repair and damage resistance. D. radiodurans is readily manipulated in the lab, so new functions can be introduced into its genome. We foresee its use for novel industrial processes that most bacteria cannot survive."

Other researchers have modified D. radiodurans to be able to degrade the organic chemical contaminant toluene and "fix" or immobilise mercury while converting it to a more benign form.

See also:

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A whale of a bug
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