Weizmann Institute scientists have found what makes the bacterium Deinococcus radiodurans the most radiation-resistant organism in the world: The microbe's DNA is packed tightly into a ring. The findings, published in the January 10 issue of Science, solve a mystery that has long engaged the scientific community, according to a press release by the Rehovot-based scientific institute.
The red bacterium can withstand 1.5 million rads - a thousand times more than any other life form on Earth and three thousand that of humans. Its healthy appetite has made it a reliable worker at nuclear waste sites, where it eats up nuclear waste and transforms it into more disposable derivatives. The ability to withstand other extreme stresses, such as dehydration and low temperatures, makes the microbe one of the few life forms found on the North Pole. Since DNA is the first part of a cell to be damaged by radiation and the most lethal damage is the breakage of both DNA strands, scientists have focused on DNA repair mechanisms to find the answer to the microbe's resilience. Cells, including human cells, can mend only very few such breaks in their DNA. Microbes, for example, can repair only three to five. Yet D. radiodurans can fix more than 200.
Using an assortment of optical and electron microscopy methods, Professor Avi Minsky of the Weizmann Institute of Science?s Organic Chemistry Department found that the microbe's DNA is organized in a unique ring that prevents pieces of DNA broken by radiation from floating off into the cell's liquids. Unlike other organisms, in which DNA fragments are lost due to radiation, this microbe does not lose genetic information, because it keeps the severed DNA fragments tightly locked in the ring - by the hundreds, if necessary. The fragments, held close, eventually come back together in the correct, original order, reconstructing the DNA strands.
The finding of a tightly packed ring made the team wonder how the bacterium could live and function under normal conditions. DNA strands must unfurl to perform their job of protein production. How can they do that if they can barely budge? This question led to the uncovering of another of the microbe's survival strategies: out of the four copies of DNA, there are always two or three tightly packed in a ring while the other copies are free to move about. Thus, at any given moment there are copies of DNA that drive the production of proteins and others that are inactive, but continuously protected.
Minsky, along with other scientists, believes that the bacterium?s answer to acute stresses evolved on Earth as a response to the harsh environments from which it might have emerged. It is one of the few life forms found in extremely dry areas. The unique defense mechanism that evolved to help it combat dehydration proves useful in protecting it from radiation.
Deinococcus radiodurans was discovered decades ago in canned food that was sterilized using radiation. Red patches appeared in the cans - colonies of the bacterium - setting off questions as to how it could have survived. Though these questions have now been answered, the tide of speculation as to how these defense mechanisms evolved - and where - is likely to continue.
The red bacterium can withstand 1.5 million rads - a thousand times more than any other life form on Earth and three thousand that of humans. Its healthy appetite has made it a reliable worker at nuclear waste sites, where it eats up nuclear waste and transforms it into more disposable derivatives. The ability to withstand other extreme stresses, such as dehydration and low temperatures, makes the microbe one of the few life forms found on the North Pole. Since DNA is the first part of a cell to be damaged by radiation and the most lethal damage is the breakage of both DNA strands, scientists have focused on DNA repair mechanisms to find the answer to the microbe's resilience. Cells, including human cells, can mend only very few such breaks in their DNA. Microbes, for example, can repair only three to five. Yet D. radiodurans can fix more than 200.
Using an assortment of optical and electron microscopy methods, Professor Avi Minsky of the Weizmann Institute of Science?s Organic Chemistry Department found that the microbe's DNA is organized in a unique ring that prevents pieces of DNA broken by radiation from floating off into the cell's liquids. Unlike other organisms, in which DNA fragments are lost due to radiation, this microbe does not lose genetic information, because it keeps the severed DNA fragments tightly locked in the ring - by the hundreds, if necessary. The fragments, held close, eventually come back together in the correct, original order, reconstructing the DNA strands.
The finding of a tightly packed ring made the team wonder how the bacterium could live and function under normal conditions. DNA strands must unfurl to perform their job of protein production. How can they do that if they can barely budge? This question led to the uncovering of another of the microbe's survival strategies: out of the four copies of DNA, there are always two or three tightly packed in a ring while the other copies are free to move about. Thus, at any given moment there are copies of DNA that drive the production of proteins and others that are inactive, but continuously protected.
Minsky, along with other scientists, believes that the bacterium?s answer to acute stresses evolved on Earth as a response to the harsh environments from which it might have emerged. It is one of the few life forms found in extremely dry areas. The unique defense mechanism that evolved to help it combat dehydration proves useful in protecting it from radiation.
Deinococcus radiodurans was discovered decades ago in canned food that was sterilized using radiation. Red patches appeared in the cans - colonies of the bacterium - setting off questions as to how it could have survived. Though these questions have now been answered, the tide of speculation as to how these defense mechanisms evolved - and where - is likely to continue.