DNA Secrets of a Salty Survivor

The Dead Sea is not so dead

But why is Halobacterium such a tenacious survivor? What caused it to evolve such dexterous DNA repair mechanisms? And how do those mechanisms work?

Jocelyne DiRuggiero, leader of the Maryland research group, has been exploring these questions for the last five years. She believes the answer stems from the fact that Halobacterium naturally lives in some rather inhospitable places: ultra-salty bodies of water such as the Dead Sea.

Most sea life would quickly shrivel up and die in the Dead Sea's briny water, which is 5 to 10 times saltier than normal seawater. The extreme saltiness damages an organism's cells, and especially the DNA inside those cells. This happens because DNA molecules are accustomed to being surrounded by a dense swarm of water molecules, and the DNA actually depends on the influence of these water molecules to keep its double-helix structure intact and to avoid damage. But in ultra-salty waters, the dissolved salt crowds out the water molecules. Partially deprived of the contact with water they need, the long strands of DNA suffer damage and even break, causing the cell to malfunction or die.

Evolving to cope with a salty lifestyle could explain why Halobacterium is so good at surviving radiation and other ravages, DiRuggiero reasons:

Credit: Purdue University The Dead Sea is 5+ times saltier than Earth's oceans. As water evaporates, salt is left behind. When the saturation point is reached, the salt forms these pillars.

"High salt concentrations lead to the same type of lesion in the DNA that does radiation," she explains. "So if the organisms are adapted to extreme saltiness, they have the machinery to repair those lesions when they encounter radiation."