Deinococcus radiodurans is a polyextremophile capable of enduring thousands of grays of ionizing radiation, a dose that shatters its double-stranded DNA into hundreds of genomic fragments. While radiation typically causes lethal genetic damage in most organisms, D. radiodurans employs a unique, highly efficient two-step mechanism to reassemble its genome.
First, the bacterium uses single-stranded annealing, mediated by specialized proteins like RecA and PprA, to rapidly stitch together overlapping DNA fragments. Next, it undergoes extended synthesis-dependent strand annealing (ESDSA), using undamaged genomic copies stored within its tightly packed, multigenomic ring structure as templates. Its cell architecture holds multiple redundant copies of its genome in a compact, toroidal shape that prevents fragmented DNA pieces from diffusing away.
Coupled with an extraordinarily potent antioxidant defense system powered by manganese ions that protect its repair proteins from oxidative damage, D. radiodurans can reconstitute a perfectly functional chromosome within hours of severe radiation exposure.