Most Radiation-Resistant Organism Decoded

Researchers have decoded genetic information on a strain of pink bacteria that can survive 1.5 million rads of gamma irradiation, a dose 3,000 times the amount that would kill a human. Benefits could include improving environmental cleanup, new industrial processes and an improved understanding of cancer.

The high dose of radiation shreds the bacteria's genome into hundreds of pieces. The organism's remarkable ability to repair this DNA damage completely in a day and go on living offers researchers tantalizing clues to better understanding the mechanism of cellular repair.

Department of Energy-funded researchers at The Institute for Genomic Research (TIGR) describe the complete genetic sequence of the bacteria Deinococcus radiodurans in the Nov. 19 issue of Science.

"This is a significant accomplishment," Energy Secretary Bill Richardson said. "The Department of Energy (DOE) began microbial genome work to support bold science and to help meet our unique environment and energy mission needs. 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 cleanup challenges."

DOE has a number of sites in its former nuclear weapons production complex that are contaminated with mixtures of highly radioactive materials and toxic chemicals. Other DOE-funded researchers have modified D. radiodurans to degrade the organic chemical contaminant toluene and "fix" or immobilize mercury while converting it to a more benign form. The engineered bacteria continues to survive in radioactive environments.

Researchers examined the bacterium's cellular repair genes and 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.

D. radiodurans was originally isolated from samples of canned meat that were thought to be sterilized by gamma radiation. Colonies of nonpathogenic bacteria growing on the spoiled meat turned out to be the radiation-resistant organism. The microbe also withstands extreme desiccation and UV-irradiation.

Since its discovery in 1956, D. radiodurans has been found around the world. Typically, it is found in locations where most other bacteria have died from extreme conditions, ranging from the shielding pond of a radioactive cesium source to the surfaces of Arctic rocks. Its name, due to its berry shape, means "strange or terrible berry that withstands radiation."

A detailed description of TIGR's genome is available through its Microbial Database on the World Wide Web at www.tigr.org. Information on DOE's microbial genome program is available at www.er.doe.gov/production/ober/microbial.html.