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Witches' Brew of Weird Bugs

October 1996

"A bubbling cauldron" is how one might describe microbiologist John Battista's lab at Louisiana State University in Baton Rouge. Here he studies pink microbes with a smell reminiscent of rotten cabbage. These "weird bugs," as he calls them, have one very important quality worth studying: they can withstand radiation 3,000 times what it would take to kill a human.

Deinococcus radiodurans, or "strange berry that withstands radiation," is the subject of Battista's NSF-supported research on how a life form can survive massive doses of radiation. When exposed to 1.5 million rads of ionizing radiation, Deinococcus repaired the damage to its shattered DNA in a matter of hours.

"There's no apparent reason for such high radiation protection on earth," says Phil Harriman, Program Director in NSF's Genetics and Nucleic Acids Program, which funds Battista's research. The rare bacterium was discovered in 1956 during experiments in which packaged food was sterilized using radiation instead of heat.

Battista has identified several aspects of the microbe's radiation-repair mechanism. It has from four to ten DNA molecules compared to only one for most other bacteria. A protein, called RecA, matches the shattered pieces of DNA and splices them back together. During these repairs, cell-building activities are shut off and the broken DNA pieces are kept in place.

Deinococcus is believed to be some two billion years old, perhaps one of the earliest life forms on the planet. One theory suggests that it may originally have come from outer space, perhaps hitching a ride on an interplanetary traveler, a chunk of rock or ice. Battista¹s work suggests otherwise.

"That journey would subject the organism to tremendous temperature extremes, and Deinococcus does not tolerate heat at all," says Battista. "We can inactivate it at temperatures as low as 45 degrees Centigrade. It seems unlikely that this bug could survive a trip through interstellar space and our atmosphere."

Battista thinks the microbe's ability to withstand radiation is related to how it survives long periods of dehydration. His work on different strains has shown correlations between resistance to radiation and resistance to dehydration.

"Cellular damage caused by dehydration and radiation are very similar," he explains. "Both cause breaks in DNA strands." Deinococcus has survived as many as 200 of these breaks to reemerge intact from the "bubbling cauldron" in Baton Rouge.

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