Researchers wake up microbes trapped in permafrost for thousands of years

In a new study, a team of geologists and biologists led by CU Boulder resurrected ancient microbes that had been trapped in ice—in some cases for around 40,000 years.

The study is a showcase for the planet’s permafrost. That’s the name for a frozen mix of soil, ice and rocks that underlies nearly a quarter of the land in the northern hemisphere. It’s an icy graveyard where animal and plant remains, alongside plentiful bacteria and other microorganisms, have become stuck in time.

That is, until curious scientists try to wake them up.

The group discovered that if you thaw out permafrost, the microbes within will take a while to become active. But after a few months, like waking up after a long nap, they begin to form flourishing colonies.

“These are not dead samples by any means,” said Tristan Caro, lead author of the study and a former graduate student in geological sciences at CU Boulder. “They’re still very much capable of hosting robust life that can break down organic matter and release it as carbon dioxide.”

Caro and his colleagues published their findings in September in the journal JGR Biogeosciences.

The research has wide implications for the health of the Arctic, and the entire planet, added study co-author Sebastian Kopf.

Today, the world’s permafrost is thawing at an alarming rate because of human-caused climate change. Scientists worry this trend could kick off a vicious cycle. As permafrost thaws, microbes living in the soil will begin to break down organic matter, spewing it into the air as carbon dioxide and methane—both potent greenhouse gases.

“It’s one of the biggest unknowns in climate responses,” said Kopf, professor of geological sciences at CU Boulder. “How will the thawing of all this frozen ground, where we know there’s tons of carbon stored, affect the ecology of these regions and the rate of climate change?”

Long slumber

To explore those unknowns, the researchers traveled to a one-of-a-kind location, the U.S. Army Corps of Engineers’ Permafrost Tunnel. This research facility extends more than 350 feet into the frozen ground beneath central Alaska.

When Caro entered the tunnel, which is about as wide as a mine shaft, he could see the bones of ancient bison and mammoth sticking out from the walls.

“The first thing you notice when you walk in there is that it smells really bad. It smells like a musty basement that’s been left to sit for way too long,” said Caro, now a postdoctoral researcher at the California Institute of Technology. “To a microbiologist, that’s very exciting because interesting smells are often microbial.”

In the current study, the researchers collected samples of permafrost that was a few thousand to tens of thousands of years old from the walls of the tunnel. They then added water to the samples and incubated them at temperatures of 39 and 54 degrees Fahrenheit—chilly for humans, but downright boiling for the Arctic.

“We wanted to simulate what happens in an Alaskan summer, under future climate conditions where these temperatures reach deeper areas of the permafrost.” Caro said.

With a twist: The researchers relied on water made up of unusually heavy hydrogen atoms, also known as deuterium. That allowed them to track how their microbes drank up the water, then used the hydrogen to build the membranes made of fatty material that surround all living cells.

Arctic summers

What they saw was surprising.

In the first few months, these colonies grew at a creep, in some cases replacing only about one in every 100,000 cells per day. In the lab, most bacterial colonies can completely turn over in the span of a few hours.

But by the six-month mark, that all changed. Some bacterial colonies even produced gooey structures called “biofilms” that you can see with the naked eye.

Caro said these microbes likely couldn’t infect people, but the team kept them in sealed chambers regardless.

He added that the colonies didn’t seem to wake up that much faster at hotter temperatures. The results could hold lessons for thawing permafrost in the real world: After a hot spell, it may take several months for microbes to become active enough that they begin to emit greenhouse gases into the air in large volumes.

In other words, the longer Arctic summers grow, the greater the risks for the planet.

“You might have a single hot day in the Alaskan summer, but what matters much more is the lengthening of the summer season to where these warm temperatures extend into the autumn and spring,” Caro said.

He added there are still a lot of open questions about these microbes, such as whether ancient organisms behave the same at sites around the world.

“There’s so much permafrost in the world—in Alaska, Siberia and in other northern cold regions,” Caro said. “We’ve only sampled one tiny slice of that.”

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