How Microbes Survive Harsh, Freezing Conditions: Life on Other Planets

Microbes may be tiny and seemingly simple, but they're crucial for understanding how life may have developed on Earth--or even other planets. Now, scientists have teamed up with NASA in order to learn a little bit more about microbes; they've examined microbial survival in ice to understand how microorganisms could survive in ancient permafrost or perhaps even buried in ice on Mars.

In order to understand how microbes might thrive in these frozen conditions, the scientists analyzed DNA. The researchers recently had results on DNA repair in ice-entrapped microbes, which could mean that the clues to their survival could also lie within this hereditary molecule.

"Microbes are made up of macromolecules that, even if frozen, are subject to decay," said Brent Christner, one of the researchers, in a news release. "We know of a range of spontaneous reactions that result in damage to DNA."

The worst kind of damage is known as double-stranded break. This is when the microbe's DNA is cleaved into two separate pieces that need to be put back together to make the chromosome functional. In fact, this kind of damage is inevitable if cells exist frozen in permafrost for thousands of years and can't make repairs. Yet surprisingly, scientists have been able to revive microbes that have been buried in ice and permafrost for thousands of years. For example, researchers managed to revive several types of bacteria from ice that is about 750,000 years old.

Needless to say, the scientists wanted to get a better look at these microorganisms in order to understand exactly how they could survive this long. In the lab, the researchers took frozen suspensions of bacteria native to Siberian permafrost and then exposed them to DNA-damaging ionizing radiation. This exposure was equivalent to what the bacteria would have experienced during hundreds of thousands of years buried in permafrost. They then froze the samples for a period of two years and checked the bacteria's DNA periodically.

It turns out that there are mechanisms that repair DNA that can operate even under freezing conditions. In fact, over the course of two years the pieces of DNA began to come back together in their proper order.

"It just keeps looking better for conditions of habitability on Mars," said Christner in a news release. "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."

The findings are published in the journal Applied and Environmental Microbiology.