An international group of researchers discovered three fungal proteins that can catalyze ice formation at high subzero temperatures. They published their findings in Science Advances. This discovery could enable scientists to engineer weather. The proteins were found in three fungal species: Mortierella alpina, Entomortierella parvispora and Podila clonocystis.
These are both liquid and frozen water droplets. They are at the same temperature, but the frozen droplets contain an ice nucleator. Photo courtesy of Boris Vinatzer.
Particles called ice nucleators, which can trigger water in the clouds to turn into ice crystals, are released into clouds, a process called cloud seeding. The ice crystals then grow as more and more water molecules stick to them. When the crystals become heavier, they fall toward the ground, melting as they pass through the atmosphere and becoming rain.
This is traditionally done with silver iodide, which is highly toxic. The researchers believe that fungal proteins could provide a better alternative. The proteins trigger freezing at temperatures as high as -2 °C, while silver iodide only works around -5 °C.
Proteins with bacterial roots
“If we learn how to cheaply produce enough of this fungal protein, then we could put that into clouds and make cloud seeding much safer,” said Boris Vinatzer, co-author of the paper and professor in the School of Plant and Environmental Sciences.
The proteins function at picomolar concentrations and remain stable across pH levels ranging from 2 to 12 and repeated freeze-thaw cycles.
The scientists also found evidence that the fungal gene encoding the ice nucleation proteins was likely acquired by a fungal ancestor from a bacterial species through horizontal gene transfer, at least hundreds of thousands of years ago, if not millions.
“It is known that fungi can acquire genes from bacteria, but it’s not something that is common,” said Vinatzer. “So I never expected that this fungal gene had a bacterial origin.”
Data from Science Advances
How genome sequencing unlocked the discovery
Researchers have known that fungi are capable of ice nucleation since the early 1990s, Vinatzer said. Recently, advances in DNA sequencing and computer science, including Illumina sequencing, allowed scientists to sequence the genomes of a specific family of fungi, the Mortierellaceae. This allowed them to discover the gene that encodes the ice nucleation proteins. AlphaFold3 was used to predict the protein structures.
While they still don’t know how fungi benefit from the acquired gene, scientists do know that the gene has been modified in fungi over the years to make it more effective. The ice nucleating proteins produced by the fungi differ from those of bacterial origin in that they are cell-free and water-soluble. These differences make the fungal molecules more appealing in bioinspired freezing technologies and engineered weather modifications.
Applications in food processing, cryopreservation and climate modeling
For example, in the preparation of frozen foods, the fungal molecule would be safer than the bacterial one because the fungus secretes the ice nucleation molecule, whereas the whole bacterial cell would be needed in the bacterial ice nucleation.
“That’s a big advantage in food production because you have just this one well-defined protein and you can get rid of everything else,” said Vinatzer, who is also affiliated with the Fralin Life Sciences Center. “There is the possibility to develop a safe, effective additive that helps in the preparation of frozen food.”
Another potential use for the proteins is in cryopreservation of cells such as tissues, sperm, eggs and embryos. The fungal ice nucleator is a relatively small molecule, said Vinatzer, so it could be added to water to make it freeze at a higher temperature to protect cells. This couldn’t be done with the bacteria because the entire bacterial cell would have to be added.
Ice nucleation is also important for climate models that predict how much radiation is reflected by clouds into space and how much reaches Earth. When clouds have ice in them, more radiation reaches the surface. The new research could contribute to developing better climate models, Vinatzer said, by making it easier to find similar molecules in the clouds.
Boise State University has submitted a patent application for the production of these proteins.
