A bacterium can have its genome shattered and stitch it back

Deinococcus radiodurans survives acute radiation of thousands of grays, which shatters its chromosomes into hundreds of pieces. It then reassembles them. A few grays kills a person.

The bacterium was found in a can of meat that had been irradiated to sterilise it and had spoiled anyway. Its trick is not a pigment that blocks radiation and not a lifestyle in reactor cores. Ionising radiation breaks DNA, in Deinococcus as in everything else. What it has, unusually, is many copies of the genome and a repair system that uses those copies as templates for each other, knitting a chromosome back out of fragments over a few hours. Thousands of grays — a gray is a joule of absorbed energy per kilogram — are survived, with growth resuming afterward. Five to ten grays, whole-body, is around the lethal range for a human who has no medical care.

The leading evolutionary story is that the repair was built for desiccation, which breaks DNA in a similar way, and that radiation resistance came along free. Dry places, not nuclear ones, are where it lives. ‘Eats radiation’ and ‘found in reactors’ are decorations. The measured thing is enough: a cell whose genome can be reduced to confetti by a dose we would call unsurvivable, and which, given water and a few hours, is a cell again, with the book put back in order.