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In a brief paper published in an issue of the journal Science, Dr. Kenneth W. Minton and an assistant, Dr. Michael J. Daly, both of the Uniformed Services University of the Health Sciences in Bethesda, Md., report the startling results of exposing (Deinococcus radiodurans) bacterium to 15,000 grays (1.5 million rads) of ionizing radiation. A dose 3,000 times as great as the lethal dose for human beings, and it shatters the bacterium's chromosomes into hundreds of fragments. But, almost miraculously, the it repairs the damage to its DNA in a matter of hours, reassembling its own chromosomes just the way they were.
The mechanism is not fully understood, but it evidently depends on the fact that each bacterium contains several copies of its chromosomes and that some of the fragments of broken chromosomes can serve as bridges to reunite broken sections.
The organism, which is generally harmless to humans, has 4 to 10 chromosomes (depending on its stage of development), each containing some three million base pairs - the letters of the chemical alphabet that spell the words of genes. When the chromosomes are smashed to pieces by radiation, pairs of surviving fragments look for "bridging" fragments to which they can temporarily attach themselves while reuniting and repairing them selves.
Proved during the last four years that this bridging, in fact, takes place although it is not clear how all the pieces in the puzzle correctly identify each other and recombine. It is still a mystery why this bacterium's ability to repair radiation damage evolved in the first place.
To protect themselves from severe stresses, some bacteria form spores, armored capsules that are more or less immune to hostile environments. But Deinococcus radiodurans, which can survive much higher doses of radiation than even spores, does not form a protective armor; it survives extreme adversity by repairing itself.
Radiation-resistant bacteria were discovered in 1956 during experiments in which packaged food was sterilized using radiation instead of the usual heat treatment. Although gamma radiation from radioactive cobalt-60 killed most spoilage organisms, in rare cases some organisms survived, reproduced and spoiled the food. Among the scientists who began studying and classifying these strange bacteria were Dr. Bevan E.B. Moseley of the University of Edinburgh, Dr. Robert G.E. Murray of the University of Western Ontario, Dr. John Battista of Louisiana State University and Minton, Louis Kervran of Biological Transmutations,Vaclav Petrik a Czechoslovakia expatriate, Louis Kervran ,a French scientists,Dr Rhadda Roy a physics at the University ofArizona.
The military was interested in the bacterium, they thought it could be used for protection against the radiation hazard of nuclear battlefields. The military has lost interest or it is said they have.
About a half dozen distinct species of the genus are now known, found in out-of-the-way places: Antarctic rocks and in water tanks used as shielding against lethal radiation from pieces of cobalt-60, and even in the feces of some elephants and South American llamas.
Other bacteria, the thermophiles, are able to survive temperatures as high as a dozen or more degrees above the boiling point of water. This has led to a hypothesis that the heat-resistant bacteria and the radiation-resistant bacteria may share kinship within a common variety, even though the heat-resistant bacteria cannot stand high radiation doses, and the radiation-resistant bacteria cannot stand high temperatures. Dr. Carl R. Woese of the University of Illinois reported detecting similarities in the ribosomal RNA of the two types of organisms, suggesting that they may be related.
Melinda Hamilton, a biologist at the Idaho National
Engineering and Environmental Laboratory (INEEL), and a team of researchers
have found that by coating contaminated concrete surfaces with naturally
occurring microbes and a nutrient mixture under high-humidity conditions,
the microbes will produce sulfuric acid. This acid then etches the
concrete surface where contamination is present.
Test trials have removed as much as 10 millimeters in 12 months.
Lowering the humidity kills the microbes, then scientists vacuum
the dust off the walls, floors, and ceiling and dispose of it. British
Nuclear Fuels Limited (BNFL) has been working with the INEEL and hopes
to apply the technology at nuclear facilities worldwide. The INEEL and
BNFL are planning a full scale demonstration at Sellafield in the
UK.
* * *
1/4/99
NATURAL INGREDIENTS
CLEAN RADIOACTIVE SOIL
Polluted and radioactive soil and waste ash
can now be cleaned with a new process based on natural ingredients
from the Department of Energy's Brookhaven National Laboratory (BNL)
in Upton, New York. The patented process, which uses simple citric
acid, naturally occurring soil bacteria and sunlight, extracts metal
contaminants from soil and wastes and converts them to a concentrated,
stable form. The process removed nearly all toxic metals and uranium from
soil from polluted sites in Ohio and Tennessee and cleaned incinerator
ash from a municipal solid waste plant. A.J. Francis, one of the co-authors
and
co-inventors of the process, said, "Since the process
separates the metals from the radioactive elements, the problem of mixed
toxic-radioactive waste disposal is solved, the amount of waste is diminished
greatly, and it's possible to reclaim the metals for a beneficial
use." Among the metals that can be separated from soil and ash are cadmium,
lead, zinc and copper. The process can remove radioactive elements such
as uranium, thorium, plutonium, cobalt, cesium and strontium. Francis reports
that the process removed 99 percent of the uranium from soil and sludge
taken from real-world polluted sites. The process is described in the current
edition of "Environmental Science & Technology."
* * *
Bug Engineered To Eat Toxic Waste
By JOSEPH B. VERRENGIA
.c The Associated Press
The bacterium Deinococcus radiodurans already holds the title as the world's toughest organism: It can survive an atomic blast. Now scientists have bioengineered it into a ``superbug'' that can digest the toxic leftovers of the nuclear age.
Government geneticists said they inserted genes from another form of bacteria into Deinococcus, producing a superbug that transforms toxic mercury compounds commonly found at nuclear weapons production sites into less harmful forms.
The scientists said the development shows how bacteria can be customized to attack the heavy metals, radioactive wastes and other substances that pollute the soil and groundwater at nuclear sites.
The superbug works in laboratory experiments but has not been tested in the field. Details of the research were published in the January issue of the scientific journal Nature Biotechnology.
The research was led by Michael J. Daley of the Uniformed Services University of the Health Sciences in Bethesda, Md.
According to a federal study, weapons waste was buried at 3,000 sites nationwide between 1945 and 1986. One-third of the sites include radioactive materials. Many of the sites were tanks and concrete-lined pits, which now are disintegrating and leaking. Cleanup estimates by the Energy Department run as high as $300 billion.
Bioremediation - a cleanup method using specialized microorganisms - may be a cheaper alternative. But conventional bacteria that gobble up solvents, metals and other forms of contamination are killed by radiation from plutonium and uranium.
Daley's lab took Deinococcus and added genes from a strain of E. coli bacteria that were resistant to particularly toxic forms of mercury.
They reported that the superbug strains proliferated when exposed to radioactive waste mixtures commonly found at weapons sites. The superbug does not neutralize radioactivity in metals.
The pink-colored bacterium smells like rotten cabbage. It was discovered in canned meat in 1956.
It is believed to be 2 billion years old, making it one of Earth's earliest life forms. Scientists believe it evolved when Earth was bombarded with more radiation than today.
It can survive 1.5 million rads of gamma radiation, or about 3,000 times the lethal dose for humans. It also can survive high doses of ultraviolet radiation and long periods of dehydration.
Previous studies have demonstrated that its radiation resistance probably involves thousands of genes. Even when hundreds of portions of DNA are damaged by radiation, the microorganism can usually repair itself in a matter of hours, using redundant genetic codes to keep functioning in the meantime.
AP-NY-12-28-99 2128EST
Copyright 1999 The Associated Press. The information contained in the AP news report may not be published, broadcast, rewritten or otherwise distributed without the prior written authority of The Associated Press. All active hyperlinks have been inserted by AOL.
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