This Fungus Can Make Water Freeze

Fungi are truly weird and impressive—they can live anywhere, be poisonous or medicinal, and, reportedly, transform plastic waste into edible ingredients. And in more fungal news, some groups of fungi can literally foster the formation of ice.

In a recent Science Advances paper, researchers describe a newly identified fungal protein that triggers ice formation at temperatures as high as 28.4 degrees Fahrenheit (-2 degrees Celsius). That’s obviously below the freezing point of water, but in nature, freezing isn’t that simple. Forming the first tiny seed of ice—an ice nucleator—takes energy, and ice forms very slowly at temperatures above -50 degrees F (-46 degrees C), according to the paper.

Yet, we still get things like clouds—microscopic water droplets and ice crystals—thanks to ice nucleators. For the new study, the team tracked the fungal gene associated with the ice-triggering protein to a distant bacterial ancestor from millions of years ago, according to a Virginia Tech statement. Importantly, the fungal protein molecule offers a non-toxic, more efficient alternative to current approaches to weather engineering, food production, or the preservation of cells and organs.

Natural ice-makers

Since as early as 1974, scientists knew that some bacterial species acted as ice nucleators—catalysts that accelerate the formation of ice crystals in nature. In 1990, researchers confirmed that some fungi were capable of this as well, as Boris A. Vinatzer, the study’s co-author and an environmental scientist at Virginia Tech, explained in the statement.

But it was only with advances in DNA sequencing that scientists could investigate microbial genomes and the relevant genetic mechanisms. And while researchers had managed to make good progress on studying these mechanisms for bacteria, not much work had been done on the origin of ice nucleation in fungal species, the team explained in a statement from Boise State University.

Finding the trigger

For the new study, the researchers studied a common soil fungus from the Mortierellaceae family, which they extracted from water and lichen samples collected during previous polar expeditions. DNA sequencing pointed the team to certain genes that closely resembled those inside known bacterial ice nucleators—not unheard of, but rare nonetheless. To check that they were on the right path, the researchers planted these proteins onto other yeast and bacteria, which indeed manifested previously non-existent ice-making abilities.

Even more remarkable was the fact that, upon further analysis, the fungus wasn’t simply copying a bacterial ancestor. Instead, it had “adopted a highly effective trait of the bacteria and adapted it to their own physiological requirements,” the team noted in the statement.

“It’s a bit the same and yet different,” explained Rosemary Eufemio, the study’s lead author and a biochemist at Boise State University. “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.”

Miracle Mortierellaceae

The study has clear implications for climate science. For one, the fungi sampled in this study are relatively common soil fungi, meaning we’re probably underestimating how much they contribute to ice formation in the atmosphere. The fungi’s natural origins also make them a non-toxic alternative to silver iodide, the go-to particle used for cloud seeding for the past 80 years, according to the U.S. Government Accountability Office.

But the team also sees fungal ice nucleators driving “evolutionary innovation at the interface of biology and physics,” it said in the paper. Experiments revealed that the fungi remained active at low concentrations and in harsh conditions. That could make them extremely useful for bioinspired freezing technologies and engineered water modifications, Vinatzer mused, unlike “bacteria, because you would have to add entire bacterial cells.”

“Now that we know this fungal molecule, it will become easier to find out how much of these kinds of molecules are in clouds,” Vinatzer said. “And in the long run, this research could contribute to developing better climate models.”