Fungal proteins secreted into soil can trigger rain formation at warmer temperatures than previously known ice-nucleating particles, according to a study published in Science Advances.
Fungal ice-making proteins work at higher temperatures than bacterial or mineral seeds
The study found that ice-nucleating proteins from fungi like Fusarium and Mortierella can cause water to freeze at temperatures as high as -2 °C, matching the efficiency of bacterial proteins from Pseudomonas syringae. These fungal proteins are water-soluble and smaller than bacterial versions, allowing them to be more easily lifted into clouds by wind. In laboratory tests, they initiated ice formation in supercooled water at temperatures where mineral dust and soot typically fail to act, requiring conditions below -10 °C or lower to be effective.
Soil-borne fungal proteins enter the atmosphere through natural wind processes
Researchers observed that when wind moves across forest floors rich in these fungi, microscopic ice-making proteins become airborne and reach cloud levels. Once in the atmosphere, they serve as nuclei for ice crystal formation in supercooled water droplets, even in relatively warm clouds above -5 °C. As ice crystals grow, they fall and melt into rain, which then returns to the soil, moistening the environment and promoting further fungal growth. This creates a potential feedback loop where fungal activity contributes to local precipitation, which in turn supports more fungal proliferation.
For more on this story, see How Forest Soil Boosts Children’s Immunity and Reduces Asthma Risk.
Fungal ice-nucleation differs from bacterial strategies in ecological impact
Unlike Pseudomonas syringae, which uses ice-nucleating proteins to damage plant tissues and access nutrients, the fungi studied appear to form symbiotic relationships with plants. Mortierella and similar genera are known to colonize root systems and enhance nutrient uptake without harming the host. This distinction suggests their role in precipitation may be a cooperative ecosystem function rather than a pathogenic mechanism. The study notes that while bacterial ice nucleation has been studied for decades, the atmospheric contribution of fungal proteins represents a newly recognized pathway in the bio-precipitation cycle.
How do fungal ice-nucleating proteins reach the clouds?
They are secreted into the soil around fungi and become airborne when wind lifts microscopic particles from the forest floor.
Why are fungal proteins more effective than dust or soot at triggering rain?
They can initiate ice formation at higher temperatures—as warm as -2 °C—where mineral particles typically require much colder conditions to work.
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