An Accidental Discovery in a Can of Meat
In 1956, Arthur W. Anderson was conducting experiments at the Oregon Agricultural Experiment Station in Corvallis. The goal was to see if high doses of gamma radiation could be used to sterilize canned food. A particular can of ground meat received a dose of radiation thought to be sufficient to kill all known life. Despite this, the meat spoiled, and from it, Anderson isolated an entirely new organism: Deinococcus radiodurans.
This extremophile is a spherical bacterium, typically 1.5 to 3.5 micrometers in diameter, that often groups together in fours to form a tetrad. It is found in a wide variety of environments, including soil, sewage, and medical instruments. The initial discovery at Oregon State University, however, is where the microbe was discovered. For his work in isolating the first radiation-resistant microorganism, Anderson received the Governor's Northwest Scientist Award in 1962.
The Machinery of Survival
Deinococcus radiodurans can withstand an acute dose of 5,000 grays (500,000 rads) with almost no loss of viability. It can even survive doses up to 12,000 grays with 10% survivability. For comparison, a dose of 5 to 10 grays is lethal to humans, and 200 to 800 grays will kill the common bacterium E. coli. This extreme resilience is not from a shield that prevents DNA damage, but from an extraordinarily efficient repair system.
The bacterium's genome is broken into four parts: two chromosomes and two plasmids. Critically, the cell maintains multiple copies of its entire genome—between four and ten, depending on its growth phase. When radiation shatters its DNA, creating dozens of double-strand breaks, the cell uses these redundant copies as a template. Specialized repair proteins, including RecA, go to work, stitching the fragmented genome back together within hours. One theory suggests its radiation resistance is a side effect of an evolutionary adaptation to survive extreme dryness, as dehydration also causes extensive DNA breakage. Further research shows a high concentration of manganese complexes that protect the cell's repair proteins, not the DNA itself, from oxidative damage during irradiation.
Scientists have genetically engineered the bacterium for bioremediation. Modified strains can clean radioactive waste sites by consuming and neutralizing toxic materials like mercury and toluene that are mixed with radioactive isotopes.