Antarctic Rotifers Revived After 24 Years: Clues from Borrowed Genes

Movement after decades in frozen storage

When water was added to a long-frozen Antarctic algal sample, tiny animals began moving again. James Raymond’s research links that revival story with a possible piece of the animals’ survival machinery: ice-binding proteins whose genes show signs of bacterial ancestry. [2]

The featured paper is peer-reviewed research published in PNAS on 4 March 2025, in the issue dated 11 March. It concerns natural organisms and laboratory assays, rather than an engineered animal or a demonstrated preservation treatment. [1]

Key findings

• Rotifers were recovered alive from material stored at −25 °C for over 24 years.
• A lab-made protein region showed ice-binding activity.
• Bacterial ancestry is supported; the precise contribution to animal survival remains unresolved. [1] [2]

An animal, not a bacterium

The animals were bdelloid rotifers, microscopic invertebrates found in wet environments. Members of the genus Adineta have elongated bodies, a flattened head, a narrow foot and three toes. A flat ciliated field on the underside of the head replaces the conspicuous paired “wheel” organs seen in many other bdelloids. [3]

The Antarctic sample was an algal community, rather than a pure culture of one identified animal species. This matters when interpreting the molecular work: DNA recovered from a community can belong to several organisms, so a promising sequence still needs a convincing biological assignment.

Why surviving ice is a complicated problem

Ice-binding proteins attach to ice surfaces and alter how ice grows. One relevant process is recrystallization: larger ice grains grow at the expense of smaller ones. Preventing that rearrangement is different from simply depressing the temperature at which ice begins growing. [4]

In a 2021 Cryobiology study, Audrey Gruneberg and colleagues compared proteins from fishes, insects, plants and microorganisms. Their ability to inhibit recrystallization did not simply track their reported antifreeze activity. The comparison is a useful reason to avoid treating every ice-binding measurement as an interchangeable test of cold protection. [4]

A protein can perform well in one assay without answering every question about an organism. For this story, the key distinction is between changing an ice surface and keeping a whole animal alive. Those are connected research questions, but they require different measurements.

What the 2025 study actually tested

Raymond analysed community DNA and compared candidate genes with published rotifer genomes. Sequence similarity, absence of introns and a shared predicted structural feature supported bacterial ancestry for rotifer genes encoding DUF3494 ice-binding proteins. AlphaFold supplied structural predictions, not direct images of molecules inside the animals. [1]

A recombinant version of one protein’s ice-binding region was tested with a maltose-binding protein tag added for solubility. At approximately 1 mg/mL, its presence produced hexagonal pits on a growing ice surface, supporting ice-binding activity. Separately, several rotifers moved within 45 minutes after water was added to material stored at −25 °C for over 24 years. [1]

These observations answer different questions. The biochemical test asks whether a selected protein region can interact with ice under laboratory conditions. The revival observation establishes that living animals could be recovered from the stored material. Connecting the two requires additional evidence about what the protein does in the animal.

How can an animal have a bacterial gene?

Horizontal gene transfer describes genetic material entering a lineage from another lineage, beyond ordinary inheritance from parent to offspring. Once acquired and retained, a gene can subsequently be inherited by descendants. “Borrowed” is a convenient shorthand for that evolutionary history; it does not mean an animal deliberately collected a useful gene.

The broader case for foreign genes in bdelloids predates the freezing study. In 2012, Chiara Boschetti and colleagues analysed the expressed genetic repertoire of Adineta ricciae. They identified many candidate genes with non-animal origins and strengthened the case using evolutionary comparisons and physical linkage to animal genes. Many candidate foreign genes encoded enzymes, suggesting a substantial contribution to metabolism. [5]

That linkage matters because environmental samples and laboratory cultures can contain microbes. Finding a bacterial-looking sequence near ordinary animal genes is more informative than finding it somewhere in a mixed sample. Several independent kinds of evidence make an evolutionary explanation more convincing.

The wider context: acquired genes can become useful

A different experiment, reported in Nature Communications in 2024, exposed Adineta ricciae and A. vaga to a fungal pathogen. Horizontally acquired genes were disproportionately represented among genes activated during infection. Some resembled microbial biosynthetic machinery associated with antimicrobial products. [6]

That study did not establish the ice-binding mechanism in Antarctic rotifers. Its relevance is broader: acquired genes can be expressed in biologically meaningful situations, rather than remaining inert additions to a genome. Even then, identifying a likely function and proving the complete pathway are separate tasks. Neither paper should be turned into a claim that every borrowed gene guarantees a survival advantage.

Why ice-binding activity is a plausible clue

There is experimental precedent for a link between microbial ice-binding activity and freezing survival. In a 2011 study, Amanda Achberger and colleagues examined a bacterium isolated from the Vostok ice core. They studied extracellular proteins, changes in ice structure and survival after repeated freezing and thawing. In their tests, extracellular protein preparations improved E. coli survival and were associated with smaller ice crystals. [7]

That was a bacterial experiment using protein preparations, not a rotifer experiment using the Antarctic animal’s gene. It therefore supports biological plausibility without supplying the missing causal test. Combining results across species can guide a hypothesis; it cannot substitute for testing that hypothesis in the system where the claim is being made.

The author’s own account of the 2025 work presents the acquired ice-binding proteins as an explanation for part of the animals’ remarkable tolerance. [2] The important word is “part”: survival over long storage need not have one molecular cause.

What remains unresolved

The study did not disable these genes in rotifers and measure the effect on freezing survival. It also left open where the proteins are expressed and whether they are secreted. The Antarctic species assignment remained unresolved. [1]

Those limits suggest useful follow-up experiments. In my assessment, independently grown cultures, measurements of protein production, and carefully matched freezing and thawing conditions would help connect sequence, biochemical activity and survival. A future perturbation experiment would need controls that distinguish loss of a freezing-specific function from general harm to the animal.

The report of several moving animals also supplies no population-wide survival percentage. A recovery observation should not be presented as a guarantee that every individual, developmental stage or species will survive the same storage conditions.

What biotechnology can learn from this

The practical opportunity is to investigate a candidate biological strategy for controlling ice, then evaluate it against a defined preservation problem. The 2021 comparison of ice-binding proteins shows why selecting the right assay matters: activity against recrystallization and activity against freezing-point depression can differ. [4]

For a future application, I would want measurements of recovery, retained function, reproducibility and performance against an appropriate existing method. A promising protein would also need to work at useful concentrations under the relevant preparation and storage conditions. These are proposed evaluation criteria, not achievements demonstrated by the rotifer study.

The memorable finding is already remarkable: living microscopic animals emerged from material kept frozen for decades. The molecular evidence makes that observation more interesting by pointing toward an evolutionary connection with bacteria. The next challenge is to establish exactly how that connection helps the animal survive.

Sources / References

1. Raymond, J. A. A horizontally transferred bacterial gene aids the freezing tolerance of Antarctic bdelloid rotifers. PNAS 122(10), e2421910122, 2025. Published online 4 March; issue 11 March.
2. Raymond, J. A. A horizontally transferred bacterial gene aids the freezing tolerance of Antarctic bdelloid rotifers. Kudos, author-contributed account of the 2025 PNAS paper, 2025 study.
3. National Institute for Environmental Studies, Japan. Adineta Morphology. The World of Protozoa, Rotifera, Nematoda and Oligochaeta, Undated taxonomic resource; accessed 30 October 2026.
4. Gruneberg, A. K., Graham, L. A., Eves, R., Agrawal, P., Oleschuk, R. D., and Davies, P. L. Ice recrystallization inhibition activity varies with ice-binding protein type and does not correlate with thermal hysteresis. Cryobiology 99, 28–39, 2021. Published online 30 January; April issue.
5. Boschetti, C., Carr, A., Crisp, A., Eyres, I., Wang-Koh, Y., Lubzens, E., Barraclough, T. G., Micklem, G., and Tunnacliffe, A. Biochemical Diversification through Foreign Gene Expression in Bdelloid Rotifers. PLOS Genetics 8(11), e1003035, 2012. Published 15 November.
6. Nowell, R. W., Rodriguez, F., Hecox-Lea, B. J., Mark Welch, D. B., Arkhipova, I. R., Barraclough, T. G., and Wilson, C. G. Bdelloid rotifers deploy horizontally acquired biosynthetic genes against a fungal pathogen. Nature Communications 15, 5787, 2024. Published 18 July.
7. Achberger, A. M., Brox, T. I., Skidmore, M. L., and Christner, B. C. Expression and Partial Characterization of an Ice-Binding Protein from a Bacterium Isolated at a Depth of 3,519 m in the Vostok Ice Core, Antarctica. Frontiers in Microbiology 2, 255, 2011. Published 26 December.