Radiation-resistant organism reveals its defense strategies

Rehovot, Israel January 9, 2003 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.

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. It is not surprising, then, that it has been the source of much curiosity worldwide, recently leading to a debate between NASA and Russian scientists the latter saying that it originated on Mars, where radiation levels are higher.

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. Thus scientists believed that the microbe must possess uniquely effective enzymes that repair DNA. However, a series of experiments showed that the microbe's repair enzymes were very similar to those existing in ordinary bacteria.

Using an assortment of optical and electron microscopy methods, Prof. Avi Minsky of the Weizmann Institute of Sciences 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 liqu

Contact: Jeffrey J. Sussman
American Committee for the Weizmann Institute of Science

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