Revived 40,000-Year-Old Microbes in the Arctic Could Release Greenhouse Gases
For tens of thousands of years, ancient microbes have lain dormant in Alaska’s permafrost, stuck in a state of suspended animation, much like the characters in Sleeping Beauty.
Today, a team of geologists writing JCR Biogeosciences awakened 40,000-year-old microorganisms and saw them develop into thriving communities.
Resurrecting ancient microorganisms
Large areas of the Northern Hemisphere are covered in frozen ground made up of ice, rocks and soil, called permafrost. These habitats provide a snapshot of the past by preserving the remains of animals, plants and even microbes.
Not only are microbes frozen in time, but some have survived millennia in these harsh, uncompromising environments by entering a state of dormancy. Indeed, previous studies have shown that certain microorganisms can be resuscitated – and remain infectious – after spending more than 40,000 years in this cryogenic state.
In addition to demonstrating the extreme robustness and impressive longevity of these tiny creatures, scientists’ ability to resurrect ancient microbes has real-world implications. Human-caused climate change is increasing temperatures in regions of the world covered in permafrost, with the Environmental Protection Agency (EPA) reporting that parts of Alaska are warming at a rate of 1.5 degrees Fahrenheit per decade. As temperatures warm and permafrost melts, these ancient microbes could be released.
Learn more: Thawing permafrost and wildfires increase CO2 emissions in Arctic tundras
Growth of microbial communities
To find out what might happen if Alaska’s summers continue to warm, researchers at the University of Colorado Boulder (CU Boulder) collected samples of near-surface and subsurface permafrost from the Alaska Permafrost Research Tunnel. The ages of these samples varied, from a few thousand years to the late Pleistocene (37,900 years ago to 42,4000 years ago).
“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 sitting there too long,” lead author Tristan Caro, a former graduate student in geological sciences at CU Boulder, said in a statement. “For a microbiologist, this is very exciting because interesting odors are often microbial.”
These samples were given water and incubated at temperatures of 39 degrees Fahrenheit (4 degrees Celsius) or 54 degrees Fahrenheit (12 degrees Celsius). Using “heavy hydrogen” (deuterium), the team was able to monitor how quickly the lipid compounds were growing and, therefore, how quickly the microbial community as a whole was multiplying.
To quote Hemingway, microbial communities grew “gradually, then suddenly.” During the first month after thawing, the study authors report that microbial growth was “extremely slow”: on some days, only one in 100,000 cells was replaced. The researchers concluded that “temperature can determine which taxa are active, but not growth rates.”
However, around the semester, things changed. Microbial communities undergo dramatic restructuring after six months, often with microbial constituents previously becoming dominant members of the community,” the researchers wrote in the JCR Biogeosciences study.
The results suggest that temperature at the time of thawing may have less influence on microbial growth than other factors, such as nutrient availability and the composition of different taxonomic groups. In the real world, this means that microbes can take months to resurrect after a heatwave. Thus, the length of summer (thaw season) may be more important than the temperatures themselves.
“There may be just one warm day during the summer in Alaska, but what matters much more is the lengthening of the summer season until those warm temperatures extend into the fall and spring,” Caro said.
From carbon sink to carbon emitter
While some studies have looked at the health implications of resurrecting ancient microbes, Caro and his team emphasize the environmental repercussions. Once released, these microbial communities break down organic matter in the environment, producing greenhouse gases including carbon dioxide and methane.
Global permafrost is estimated to contain twice as much carbon as the current atmosphere. Thus, the permanent thaw transforms what was once a carbon sink into an emitter. This will only exacerbate warming trends, although the magnitude of this phenomenon is uncertain: “This is one of the biggest unknowns in climate responses,” co-author Sebastian Kopf, a professor of geological sciences at CU Boulder, said in a statement.
The team hopes future research will focus on different types of permafrost found in Alaska and elsewhere.
Learn more: How a worm came back to life after 46,000 years frozen in Siberian permafrost
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