Scientists Find Antarctic Bacteria That May Exist Nowhere Else On Earth

Isolated for Millions of Years, These Bacteria May Belong Only to Antarctica

Antarctica’s soil looks like nothing could survive there: barren, frozen, and bone dry most of the year. Yet a new study finds that a common group of soil bacteria appears to have its own private club there, with most of its Antarctic strains found nowhere else in the study.

Researchers examined a bacterial genus called Arthrobacter, a hardy microbe found in soils across the globe, from farmland to forests to deserts. After comparing hundreds of soil samples from Antarctica and elsewhere, the team discovered that 90% of the Arthrobacter strains living in Antarctic soil turn up nowhere else in the study. Antarctica appears to harbor its own collection of Arthrobacter strains, most of which were not detected anywhere else in the researchers’ sampling.

Published in the Proceedings of the National Academy of Sciences, the findings offer evidence that microorganisms, not just plants and animals, can become restricted to particular places. Scientists have long known about endemic species like Darwin’s finches in the Galápagos or koalas in Australia. Finding the same pattern in soil bacteria, organisms capable of drifting long distances on wind currents, shows that even microbes capable of traveling that far can still end up geographically restricted.

Antarctic Bacteria Turn Out to Be a World Apart

To test whether Antarctic bacteria were truly unique, the research team, led by Nicholas Dragone and Noah Fierer of the University of Colorado Boulder, analyzed 598 soil samples: 126 collected from ice-free patches across Antarctica and 472 gathered from non-Antarctic locations worldwide, including farmland, forests, deserts, and other cold climates like the Arctic and the Tibetan Plateau.

Rather than simply asking whether Arthrobacter existed in a sample, the researchers drilled down to the strain level, identifying individual genetic “family lines” within the genus. Two bacteria can belong to the same broad genus while being genetically distinct enough to count as different strains, much like golden retrievers and chihuahuas are both dogs but clearly not the same animal.

Using a reference database of 568 known Arthrobacter strains, the team found 36 strains in Antarctic soils and 111 in soils from the rest of the world. Only four strains overlapped, far fewer than chance would predict.

Researchers also wanted to know whether Antarctic Arthrobacter had evolved special traits for their harsh surroundings, so they grew 53 strains, split roughly evenly by origin, under a range of lab temperatures and moisture levels.

Antarctic strains grew best at noticeably cooler temperatures than non-Antarctic strains, averaging about 62 degrees Fahrenheit versus roughly 82 degrees, and grew more than three times slower overall, even at each strain’s own ideal temperature. Genetic analysis backed this up: Antarctic strains carried smaller genomes with fewer genes tied to energy-intensive activities like movement and cell wall construction, a signature common in organisms adapted to nutrient-scarce environments. They also carried far more genes associated with movable pieces of DNA, which can help bacteria exchange genetic material with one another. The researchers suggest this kind of gene swapping may have played an unusually important role in their evolution, especially in an environment where the bacteria are expected to reproduce slowly.

These Antarctic Bacteria Like It Surprisingly Warm

One puzzle stood out. The bacteria’s ideal growth temperatures, while cooler than average, were still far warmer than actual Antarctic soil temperatures, which can plunge below negative 30 degrees Fahrenheit. Study authors suspect the bacteria stay dormant most of the year, then activate during the brief polar summer, when direct sunlight can warm exposed soil well above freezing for nearly 24 hours a day.

One expectation did not hold up, however: researchers predicted Antarctic bacteria would be unusually good at surviving extreme dryness, given how parched the continent’s soils are. Instead, Antarctic strains proved somewhat less drought-tolerant than their counterparts, at least under lab conditions.

Millions of Years of Isolation Left a Mark on These Bacteria

Antarctica’s deep history of isolation likely helps explain why so many of these strains are geographically distinct, the study’s authors say. The continent has been thermally and climatically isolated for tens of millions of years, following the onset of major glaciation roughly 34 million years ago and the development of circumpolar circulation around Antarctica. A ring of atmospheric circulation around the continent, the circumpolar vortex, further limits how easily anything, including microscopic organisms, drifts in or out on the wind. Antarctic strains still carry lower overall genetic diversity than the global Arthrobacter pool, hinting at a shared evolutionary history shaped by repeated cycles of glaciation and thaw.

Researchers have found pockets of microbial endemism in Antarctica before, mostly in isolated spots like geothermal vents on Mount Erebus. This study is notable because it finds the same pattern in ordinary soil, an environment usually considered too diverse and interconnected for endemism to take hold. The finding also raises a broader question about how these isolated microbial communities could change if Antarctic conditions shift.

Arthrobacter is found in soils around the world, yet Antarctica appears to harbor a version that belongs almost entirely to itself. Whether that distinction persists as Antarctic conditions change remains an open question worth watching closely.

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Disclaimer: This article is based on findings from a peer-reviewed scientific study and reflects the results and interpretations reported by its authors at the time of publication. Scientific understanding can evolve as new research emerges.

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