Fungal ice-triggering proteins reveal an ancient bacterial inheritance

Ice needs a starting point

Water cooled below zero does not always turn immediately into ice. The formation of a first stable crystal nucleus depends on conditions and on suitable surfaces or molecules. Some microorganisms produce proteins that make this step easier. A study published on 11 March 2026 in Science Advances investigates the genetic and structural basis of this activity in fungi belonging to the Mortierellaceae. The original paper by Eufemio and colleagues.

The team examined an ice-active strain of Mortierella alpina and a fungus isolated from a lichen, among other material. Genome sequencing identified genes related to bacterial ice-nucleating protein genes. Analyses of their relationships suggest an ancient transfer from bacteria into an ancestor of the studied fungi. This is an evolutionary inference from sequences, rather than a direct observation of gene transfer taking place in a present-day forest.

A protein that works without a membrane

The fungal proteins differ from well-studied bacterial counterparts. They are water-soluble and can function independently of a cell membrane. The authors related their structure and formation of larger molecular assemblies to their stability and ice-nucleating activity. A related genetic instruction has therefore been used within a different biological arrangement.

To test the proposed genes’ function, the researchers introduced selected sequences into yeast and bacteria that were previously not ice-active. The resulting ability to initiate freezing supported a link between the genes and the physical property. This is a stronger test than simply finding a similar sequence in a database, although it does not answer every question about the organism’s activity in nature.

Nucleation should also be distinguished from cooling. A protein helps initiate the transition in sufficiently supercooled water; it is not a biological refrigerator that can freely lower environmental temperature. Consequently, the statement “fungi make ice” needs details about which fungi, under what conditions and through which mechanism. Without that context, an accurate laboratory result can easily become an exaggerated general claim.

From droplets to possible applications

Ice-nucleating activity is relevant to research on aerosols and clouds because droplet freezing can affect subsequent atmospheric processes. However, the molecular study does not measure how much these particular fungi contribute to rainfall above a specific forest. Explaining a molecular mechanism and quantifying its atmospheric importance are different research tasks.

The Max Planck Society announcement also identifies possible applications in controlled freezing. Soluble molecules may be easier to incorporate into technological workflows than systems that require membranes. Preserving biological material, processing food and producing snow remain directions for development, rather than a list of finished products demonstrated by this experiment.

The compelling connection is between two histories: an ancient exchange of genes across distant groups of organisms, and a physical property that can be tested in a droplet of water. Identifying that connection makes further questions more precise. Researchers can investigate where the proteins occur, how long their activity persists, and what they change outside the laboratory, while keeping those wider ecological and practical possibilities separate from the findings already established.