show that high cytosolic manganese and low iron concentrations facilitate resistance by protecting proteins, but not DNA, from IR-induced oxidative damage. In a new study investigating the functional consequences of this disparity, Daly et al. The researchers showed that the most resistant cells contained about 300 times more manganese and three times less iron than the most sensitive cells. found that IR-resistant and IR-sensitive cells had significantly different mineral concentrations, lending support to a role of manganese and iron in recovery. Or maybe thereвЂ™s something special in the way the microbe packages its chromosomes.ДЄ 2004 study by Michael Daly et al. radiodurans genome encode proteins with novel repair functions? Or perhaps resistant bacteria can use standard DNA repair equipment in ways other organisms cannot. Might the hypothetical genes identified in the D. radiodurans, which can weather the 100 double-strand breaks per genome caused by much higher doses just fine. Shewanella oneidensis, for example, cannot survive doses causing less than one double-strand DNA break per genome although it encodes DNA repair systems that appear more complex than those in D. And it appears that bacteria at the opposite ends of resistance sustain about the same amount of DNA damage from a given IR dose, with many bacterial species succumbing to IR doses that cause very little DNA damage. radiodurans genome, sequenced in 1999, revealed nothing clearly unusual about its DNA repair components. Over the past few years, several observations have challenged the DNA-centered view of IR toxicity. And no matter how efficient DNA repair enzymes might be under normal conditions, itвЂ™s not clear how they manage to resurrect a radiation-shattered genome if they are also damaged. Surprisingly, this extremophile relies on a set of apparently universal DNA repair proteins, raising an even bigger paradox: DNA repair and synthesis depends on proteins, but these proteins suffer radiation damage, too. radioduransвЂ™s resistance have focused on the mechanisms of DNA repair, with each study revealing seemingly greater levels of efficiency. Within this framework, efforts to understand D. Researchers investigating the nature of radiation toxicity long ago settled on DNA as its principal target. This extremely resilient microbe can endure 100 times the IR levels that kill other bacteria and levels 2,000 times higher than the lethal human dose. Inside the bulging cans, they discovered a strain of bacteria now called Deinococcus radiodurans. Fifty years ago, scientists experimenting with gamma radiation to sterilize canned foods were surprised to find spoiled meat in cans zapped with what they thought were lethal levels of ionizing radiation (IR).

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