When you go to the dentist to have your jaws X-rayed, you’ll notice that you have to wear a heavy lead apron—and the person who takes the X-ray leaves the room to do it. X-rays are safe, but these precautions give you some sense of how careful we have to be around even relatively harmless levels of radiation. The problem is that unsafe levels of radiation can mess with the cells and molecules in our body, warping them and even breaking them apart. It does the same thing to microbial cells.
But there’s one bacterium called Deinococcus radiodurans that can live through blasts of radiation thousands of times greater than the level that would kill a human being. Radiation is measured in units called rads. A dose of 500 to 1,000 rads is enough to kill a person. D. radiodurans thrives even after being hit by up to 1,500,000 rads—yikes!