Researchers Discover How Microbes Survive in Freezing Conditions

By studying DNA repair in ice-entrapped microbes, researchers from Louisiana State University have discovered how microbes are able to survive under frozen conditions.

"Microbes are made up of macromolecules that, even if frozen, are subject to decay," Brent Christner, an associate professor of biological sciences, said in a press release. "We know of a range of spontaneous reactions that result in damage to DNA."

The most intense damage is a double-stranded break, or when the microbe's DNA cleaves into two.

"This kind of damage is inevitable if cells exist frozen in permafrost for thousands of years and cannot make repairs," Christner said. "Imagine that a microbe is in ice for extended periods of time and its DNA is progressively getting cut into pieces. There will eventually be a point when the microbe's DNA becomes so damaged that it's no longer a viable informational storage molecule. What is left is a corpse."

Still, for reasons that were not always clear, scientists have successfully revived microbes that lay buried in ice for up to millions of years.

To better understand why, Christner and colleagues took frozen suspensions of bacteria native to Siberian permafrost and exposed them to radiation equal in terms of damage to what microbes would have experienced during roughly 225,000 years of permafrost. They then incubated the microbes at 5 degrees Fahrenheit for two years.

The researchers were surprised to find that during this time, the pieces of DNA came back together in their original place, suggesting that the mechanisms tasked with repairing DNA are able to operate even under freezing conditions.

"This isn't a random process," Christner said. "This tells us that the cells are repairing their DNA. This is important because we don't typically think of these as being conditions under which complex biological processes are going on."

Based on this, Christner argues that it's reasonable to believe that in the case that life ever evolved on Mars, and microbes are still frozen somewhere on the planet, they might still be viable under the right circumstances.

"It just keeps looking better for conditions of habitability on Mars," Christner said. "This is relevant in an astrobiological sense because if these DNA repair mechanisms operate in Earth's cryosphere, extraterrestrial microbes might be using this survival mechanism to persist on other icy worlds in the solar system. We are very excited about these results."