Genetic Information Of World's Most Radiation-Resistant Organism Decoded

Rockville, MD - No, it's not the cockroach, but rather 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. This 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. Advances in this area could in turn improve our understanding of cancer which is frequently caused by unrepaired DNA damage. Genetically engineering the microbe could lead to improved ways to cleanup pollution and to new industrial processes.

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

"This is a significant accomplishment," Secretary of Energy Bill Richardson said. "The Department of Energy 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."

"We anticipate a terrific boost for industrial and environmental microbiology," said TIGR President Claire Fraser. "Publication of the Deinococcus sequence will foster more research into cellular repair and damage resistance. D. radiodurans is readily manipulated in the lab, so new functions can be introduced into its genome. We foresee its use for novel industrial processes that most bacteria cannot survive."

The Department of Energy 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 be able 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.

TIGR investigator Owen White led the team that determined the order of all of the nearly 3.3 million individual chemical base units making up D. radiodurans' DNA. They found the bacteria's genome is composed of two circular chromosomes that are about 2.6 million and 400,000 base pairs in length. The genome also is composed of two smaller circular molecules, a megaplasmid of 177,000 base pairs and a plasmid of 45,000 base pairs. Other bacteria with multiple chromosomes or megaplasmids are known, but D. radiodurans represents the first completely sequenced bacterium with these features.

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. Evolutionary analysis suggests the smaller chromosome, plasmid and megaplasmid may have been acquired some time after the origin of the Deinococcus lineage. Further analysis will be required to determine if the evolutionary formation of these smaller structures is directly responsible for D. radiodurans' ability to survive extreme environmental conditions.

D. radiodurans was originally isolated from samples of canned meat that were thought to be sterilized by gamma radiation. Colonies of non-pathogenic 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."

The Department of Energy funded TIGR's work as part of the department's microbial genome program. Researchers have sequenced 11 microbes since the program began in 1994 as a spin-off of the human genome program; 15 others currently are being sequenced. Through the study of microbes, the program seeks biological approaches to solving challenges in environmental cleanup, energy production and use, climate change, industrial processes, medicine, agriculture and biological nonproliferation (understanding and detecting biowarfare agents).

Kenneth W. Minton and Michael J. Daly with the Uniformed Services University of the Health Sciences performed the genetic engineering research on D. radiodurans for the Department of Energy and collaborated with TIGR on the sequencing project.

###TIGR is a not-for-profit research institute founded in 1992 by J. Craig Venter. TIGR conducts structural, functional and comparative analyses of genomes and gene products in viruses, bacteria (pathogenic and environmental), archaea and eukaryotes, both plant and animal, including human. In 1996, TIGR made news worldwide by determining the genome of the microbe Methanococcus jannaschii. This research confirmed the uniqueness of a third major branch of life on earth, the archaea.

A detailed description of its genome is available through TIGR's Microbial Database on the World Wide Web at http://www.tigr.org.

Information on the Department of Energy's microbial genome program is available at http://www.er.doe.gov/production/ober/microbial.html.