Certain fungi possess the capability to generate proteins that freeze water, a feature that might enable them to ascend into the atmosphere and trigger rainfall. Scientists have now unearthed the secret behind this mechanism: a gene originating from ancient bacteria. The findings of a new investigation were published in the journal Science Advances.
It has long been established among researchers that some bacteria incorporate proteins into their cell membranes that facilitate the freezing of water at relatively warm temperatures, around minus 5 degrees Celsius—a phenomenon termed ice nucleation. A number of fungal species share this capacity, yet considerably less was understood regarding its workings within this biological kingdom.
“Our sole aim was to comprehend the underlying process,” stated co-author Boris Vinatzer from Virginia Tech.
Vinatzer and his team analyzed the genomes of two fungal strains belonging to the Mortierellaceae family to pinpoint their ice-nucleating protein. They had a few initial leads: they knew the protein was released into the surroundings rather than adhering to the fungal cells, and they had a rough idea of its size. Consequently, they searched for genes exhibiting these traits and bearing resemblance to known bacterial ice-nucleating proteins.
To their surprise, they identified a candidate gene nearly identical to a bacterial gene known as InaZ. Furthermore, upon transferring this fungal gene into a yeast cell, the yeast also gained the ability to generate ice.
“We confirmed that this specific segment of DNA is responsible for producing the proteins that promote ice formation,” he remarked.
This observation strongly suggests that at some juncture in the distant past, perhaps millions of years ago, an ancestral fungus acquired this gene from its bacterial neighbors—a process termed horizontal gene transfer—and subsequently adapted it for its own use.
However, the precise manner in which fungi exploit this ice-forming ability and what evolutionary advantage it confers remains less clear. “As of now, we truly are uncertain,” noted Vinatzer.
Bacteria equipped with ice-nucleating proteins frequently afflict plants, such as Pseudomonas syringae, which attacks corn. Scientists theorize that these bacteria utilize the ice-forming proteins to inflict damage upon the plant, thereby allowing nutrients to leach out or granting the bacteria entry.
One of the fungi examined in the recent study was isolated from a lichen—a composite colony of fungi and algae growing on rocks and trees. Vinatzer conjectured that the ice-promoting proteins might allow the fungus to harvest moisture directly from the air, thereby supplying the lichen with a much-needed yet scarce resource.
“During the mornings, when humidity is high and temperatures are low, the fungal proteins could induce frost formation on the lichen, which subsequently melts and provides water later in the day,” he explained.
But perhaps the most compelling aspect of these ice-forming bacteria and fungi is their potential to influence weather patterns by seeding clouds to induce precipitation.
Ice-nucleating bacteria like P. syringae are known components of the water cycle and play a significant role in precipitation formation. They are carried aloft into clouds by wind or evaporation, where their ice-nucleating capability leads to the formation of tiny crystals that eventually grow large enough to fall as rain or snow. According to Vinatzer, it is probable that the ice-nucleating proteins secreted by fungi undergo a comparable process.
Since a single fungus can release numerous proteins, each acting as an individual ice nucleus, their presence in clouds could far surpass that of rain-inducing bacteria. “This suggests that fungi might actually be more significant than bacteria in impacting weather,” he concluded, adding that this could benefit not only the fungi on the ground but the entire ecosystem.
Vinatzer proposed that these newly discovered fungal proteins could also offer advantages to humanity. Currently, the artificial induction of ice crystal formation relies on a toxic chemical known as silver iodide, but it might be feasible to substitute this with a harmless organic protein.
“These proteins could serve as an alternative to toxic silver iodide,” Vinatzer stated. “If we can figure out how to manufacture them, why wouldn’t we use them instead of silver iodide?”
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