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An international research team led by Konrad Meister from the Max Planck Institute for Polymer Research, part of Mischa Bonn's department, has identified a new class of ice crystal-forming proteins in lower fungi. The study shows that fungi of the family Mortierellaceae use a genetic blueprint that originates from bacteria. Unlike bacteria, however, the fungi use the gene to form water-soluble proteins. This structural adaptation explains the high stability and efficiency of ice formation by the fungi. According to the researchers, the fungal proteins are promising for applications in the field of freezing technology.
· Genetic origin: The study shows that the fungi produce proteins that originally come from bacteria to freeze ice.
· Ice nucleation: The ability to nucleate ice could be evolutionarily important for microorganisms, offering them survival advantages in the atmosphere.
· Practical applications: The newly identified proteins could be important in the cryopreservation of cells and organs, in food processing, and in snow production.
Water freezes at 0 °C—at least according to school textbooks. But under ideal conditions, pure water remains liquid down to a temperature of −40 °C. A small shock or a dust particle is then enough to cause the liquid to abruptly and suddenly turn into ice. Some types of bacteria are also good ice formers because they produce special proteins that promote freezing at temperatures around 0 °C. For example, proteins from the bacterium Pseudomonas syringae cause water to freeze better than any other known material. Such ice nucleation proteins are found not only in bacteria, but also in some fungi. While the structure of bacterial proteins has been well studied, that of fungi has remained unclear until now.
The international team led by Konrad Meister from the Max Planck Institute for Polymer Research describes for the first time a new class of ice nucleation proteins from the Mortierellaceae family of fungi. This family belongs to the lower fungi, which also include yeasts. The work was carried out in collaboration with researchers from the Max Planck Institute for Chemistry and US colleagues, including Boris Vinatzer from Virginia Tech.
To uncover the structure of the fungal proteins, the researchers sequenced the genomes of ice-active fungi isolated from water samples and lichens collected during previous polar expeditions. In doing so, they discovered genes closely related to a gene already known from ice-active bacteria such as Pseudomonas syringae: The gene InaZ is the template for making ice nucleation proteins.
Gene transfer across species
However, during structural analysis, the researchers discovered significant differences. Unlike the bacterial proteins, which must be embedded in a membrane to function, fungal proteins are water-soluble and unusually stable.
Based on phylogenetic analyses – i.e., analyses of the origin of a gene – the team concluded that the InaZ gene was most likely transferred from bacteria to a fungal ancestor across species in the distant past. Instead of developing ice nucleation independently, the fungi adopted a highly effective trait of the bacteria and adapted it to their own physiological requirements.
“It's a bit the same and yet different,” says Rosemary Eufemio, a researcher at Boise State University in the US. “Fungi use the same repetitive sequence architecture as bacteria for their ice-forming sites, but have made them more soluble and stable, which probably benefits their ecological function.”
To prove that the identified fungal genes are indeed the template for ice-nucleating proteins, the research team transferred two of the identified genes into non-ice-active yeast and bacteria. The modified microorganisms then became ice-active, which confirmed the functional connection.
Applications in cryopreservation conceivable
In addition to the biological significance of the discovery, Konrad Meister from the MPI for Polymer Research also sees concrete practical applications in technologies based on controlled freezing. "Soluble ice-nucleating proteins are easier to isolate, handle, and integrate into formulations and technological processes than membrane-bound ones. This opens up new possibilities for controlled freezing in the cryopreservation of cells and organs, food processing, and snow production."
Ice nucleation: Properties and significance
The ability to nucleate ice—i.e., to form ice nuclei in a targeted manner—is of great evolutionary importance for certain microorganisms. It gives them survival advantages, especially in the atmosphere. When ice forms in clouds, the frozen droplets fall to earth as precipitation. “This allows bacteria and fungal spores to be transported over long distances and reach new habitats such as plant surfaces, soils, or other geographical regions,” explains biologist and Earth system researcher Janine Fröhlich from the Max Planck Institute for Chemistry.
A well-known example is Pseudomonas syringae, which is commonly found on plant leaves. By triggering ice formation on the leaf cells, it causes frost damage. This causes plant sap to leak out, which serves as a nutrient source for the bacteria – in other words, they deliberately damage the plant in order to feed.
In addition, ice-nucleating bacteria have a climatic significance: they are among the most effective natural triggers of ice formation in clouds and can thus influence precipitation, weather events, and the global water cycle.
The researchers report their findings in the study “A Previously Unrecognized Class of Fungal Ice-Nucleating Proteins with Bacterial Ancestry” in Science Advances.
Prof. Dr. Konrad Meister
Max Planck Institute for Polymer Research
Phone: +49 6131 379-157
Email: meisterk@mpip-mainz.mpg.de
and
Boise State University
1910 University Dr.
Boise, ID 83725
USA
Email: konradmeister@boisestate.edu
Phone: +1 (208) 426-5716
A previously unrecognized class of fungal ice-nucleating proteins with bacterial ancestry
Rosemary Eufemio, Mariah Royas, Kaden Shaw, Ingrid de Almeida Ribeiro, Hao-Bo Guo, Galit Renzer, Kassaye Belay, Haijie Liu, Parkesh Suseendran, Xiaofeng Wang, Janine Fröhlich-Nowoisky, Ulrich Pöschl, Mischa Bonn, Rajiv Berry, Valeria Molinero, Boris Vinatzer, Konrad Meister
Sci. Adv.12, eaed9652(2026).
https://doi.org/10.1126/sciadv.aed9652
Fungi have adapted genes from bacteria through evolution and can thus freeze water more easily.
Copyright: © Katharina Maisenbacher / MPI-P
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