14 DAY TRIAL // X rays are known to destroy virtually all bacteria (and life forms).
But there is a bacterium that stands immense doses of ionizing radiation without any problem. However, scientists were surprised to find that the bacterium's resistance doesn't come from protecting its DNA - as most researchers had thought - but from its proteins.
This discovery challenges the conventional concept of radiation damage, and points at new ways of cleaning up radioactive waste, offering at the same time hope for safer X-ray therapy.
The bacterium Deinococcus radiodurans ("terrific berry that withstands radiation") can resist radiation doses of up to 10,000 Grays (Gy), which generally kill all the other bacteria and cells. (Humans "check out" at 10 Gy). "Radiation damages the DNA of different bacterial species to the same degree, so the superbug must be protecting some other system critical to its survival", explained Michael Daly, a radiation biologist at the Uniformed Services University of the Health Sciences in Bethesda, Maryland.
He had already found out that the proteins of D. radiodurans' DNA repair systems function much more efficiently than in other bacteria.
The metal manganese, which is at levels 300 times higher in D. radiodurans could be the responsible.
Now, Daly's team examined manganese's ability to stop the damaging free radicals resulted from radiation. A manganese-based chemical complex in D. radiodurans was found to inactivate the free radicals that damage proteins but not those that attack DNA. "Proteins in sensitive bacteria are much more sensitive to radiation than DNA. If you can protect proteins from radiation, you're in a good position to recover", Daly said.
The manganese complex could be added to microbes to better clean up radioactive waste, for example. The complex could also increase the radiation-resistance of human cells, speeding recovery after radiation therapy. "The ideas presented differ radically from mainstream thinking concerning bacterial radioresistance," said John Battista, a microbiologist at Louisiana State University in Baton Rouge. "Although more experiments are needed, the study indicates that the rest of us have been searching for the answers to radioresistance by studying the wrong target", Battista said.
David Thaler, a microbiologist at Rockefeller University in New York City, believes that manganese could have a second role of improving the capacity of certain proteins to fix damaged DNA. "Studies have shown that the metal can increase the ability of the enzymes to fix broken chromosomes and its high levels in D. radiodurans may give the bacterium a critical boost."