Summer 2009
After a dose of radiation that would kill most things, these pink-hued bacteria piece themselves back together and live on.

The microbe Deinococcus radiodurans is one resilient bug. Even when exposed to levels of radiation that would reduce a drinking glass to a pile of brown crumbles, the bacterium won’t die. Instead it goes about sorting and reassembling its fractured DNA, re-emerging whole in a mere three hours.

“Like a phoenix,” says Michael Cox, a professor of biochemistry who studies the bacterium, “it rises from the ashes.”

Scientists have worked for years to understand how D. radiodurans pieces itself back together, a process that Cox describes as the most amazing DNA-repair mechanism in all of biology. Now they’re entertaining an even more far-reaching possibility: that D. radiodurans could be used to reassemble human DNA.

As forensic scientists and CSI fans know, DNA is fragile, easily damaged by sunlight, heat, water and even just the passage of time. This means that the genetic trail in crimes quickly grows cold. If DNA recovered from a crime scene is damaged, it can reveal little about the identity of suspects.

But what if the DNA could be fixed? After a scientist in California’s Orange County Forensic Science Services lab posed that question, Cox pursued a grant from the U.S. Institutes of Justice to explore the idea. “Nobody has ever gotten DNA double-strand break repair to work from an extract,” he says. “But these bacteria should give us the best chance of making it happen.”

D. radiodurans cells keep multiple copies of their chromosomes on hand, which allows them to sort through DNA fragments, match overlapping pieces and stitch them back together. Cox is currently mixing samples of damaged DNA with cellular extracts from D. radiodurans to see if the bacterium can sort through human DNA, as well. If it can, the experiment could reveal a potent tool for solving cold-case crimes. But it also could help scientists figure out their own mystery: what genes the bacterium uses to accomplish its reassembling magic.

To learn this, Cox has exposed normal E. coli bacteria to successive doses of near-lethal radiation to identify mutant strains able to withstand radiation. But so far each experiment has led to a different group of candidate genes. “What this has told us at a minimum is that there are multiple paths to get to this phenotype,” he says. And that means the case of D. radiodurans remains a genetic whodunit—for now.

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