I Thought All Water Freezes at 32° F, I was Wrong

Biological organisms influence the temperature water freezes at

Hiya!

On one level, I know everything is connected. It’s one of those simple yet profound facts of the Universe, even if we can’t see or comprehend the vast thread(s) connecting it all. The evidence is there, and we’re discovering more all the time.

For instance, ice might seem pretty straightforward. It’s common knowledge that water freezes at 32° F (0° C), right? Actually, pure water freezes at much colder temperatures. The reason water freezes at 32° F (0° C) is biological, but it’s little understood. Thankfully, new research inches us slightly closer to some answers.

Ice Nucleators 

I was today years old when I learned that water doesn’t naturally freeze at 32° F (0° C). I mean, it does naturally freeze at that point, but pure water only freezes when temperatures fall to a frigid -50.8° F (-46° C). Ice typically freezes at warmer temperatures because organisms such as bacteria, insects, and fungi living in the water kickstart ice formation.

These microscopic life forms produce proteins called ice nucleators, which initiate the nucleation (transformation) process of ice forming at warmer temperatures than pure water would naturally freeze at. Nucleation is the process that occurs when substances change state. In this case, we’re talking about water turning into ice. Meanwhile, ice nucleators speed nucleation up.

See, for a crystal to form, H2O molecules must order themselves into specific arrangements of rigid lattice structures, which begin with a tiny grouping of latticed molecules, or “nuclei.” The larger the nucleus, the more water molecules can accumulate on it until an ice crystal eventually forms.

This process is challenging for pure water to complete on its own because its molecules are bustling around, and getting them to slow down to form a nucleus is challenging, but the ice nucleator proteins help water molecules collect into a nucleus.

Some bacterial nucleators are so good at this that they’re used to create snow at ski resorts. However, many different organisms have evolved various ways to control the nucleation process for forming ice. The various species belong to multiple biological kingdoms, but the ability is thought to have evolved independently — a phenomenon known as convergent evolution.

Now, researchers want to better understand the “why” of this process. Is it an evolutionary solution to surviving colder environments? Is ice production the goal of this process or a byproduct of something else?

While bacteria have been studied the most, a theoretical chemist and researcher, Valeria Molinero of the University of Utah and a professor of chemistry and researcher, Konrad Meister of Boise State University of Idaho, led a team of international scientists to investigate more about how this process works for fungi and why fungi make these proteins at all.

New Study

Molinero worked with a team of experts from Germany’s’ Max Plank Institute for Polymer Research, Idaho’s’ Boise State University, and The University of Utah to study the ice nucleators made by the fungus Fusarium acuminatum.

The team discovered the fungus produces ultra-tiny protein subunits that aggregate into larger particles that can both encourage and hold back ice formation more efficiently than many other organisms. In November 2023, they published their study in the Proceedings of the National Academy of Sciences (PNAS), in which they wrote:

“We find ice-binding and ice-shaping activity of Fusarium [ice nucleators], suggesting a potential connection between ice growth and inhibition.”

In addition to encouraging or discouraging ice production, Fusarium nucleators are also highly effective and efficient. Meister, Molinero, and their team discovered these fungal proteins are notably smaller than the proteins produced by bacteria and other organisms.

They also found that many of these proteins bond into complex structures to help ice nucleate. Even when the researchers decreased the levels of Fusarium proteins, they still triggered the nucleation process.

Meister told Brian Maffly at The University of Utah that other organisms besides fungi can form larger aggregates from smaller building blocks. But that,

"Nevertheless, we were surprised by the small size of the fungal protein building blocks compared to their efficiency. Other known and similarly efficient ice-making proteins from other organisms, for example, are 25 times larger."

Why?

Now, the question is why this happens. Why produce many small proteins that need to be organized so efficiently? The researchers have an idea. They write in the study:

“We expect that the energetic benefit for the organism in producing smaller proteins, rather than a single large one, contributes to the success and adoption of [this] strategy across species that are not evolutionary-related.”

All living things strive to be efficient with their energy. Bacteria and fungi are no different. Producing many small proteins over one large one makes evolutionary sense and is a strategy many species use. Consider all the species that lay numerous eggs, which increases the odds that at least a few offspring will survive to adulthood.

Still, another question remains: Are these proteins meant to promote ice formation, or is ice formation a side effect of some other benefit the proteins provide the fungus? The scientists don’t have an answer yet, but other creatures, like frogs, could help future researchers find out.

Many frog species naturally produce antifreeze to remain alive when they fall into a state of inactivity during winter. They may become covered in ice, but their cells create ice nucleators, which help the fogs control where the ice forms, thus keeping them alive. Well, that and an antifreeze made of glucose and urea. Some frog species will even ingest bacteria to help the process.

So, might it be possible that fungi nucleators are part of a similar antifreeze system? No idea, but it’s worth exploring.

In the Future

While the researchers are researching, it’s worth discussing why any of this matters — besides sheer curiosity and the fact that it’s super cool.

Once ice nucleators are better understood, they could be used in various industries, from biology and mineralogy to food engineering. Ice nucleators could create more efficient methods of freezing food, tissues, organs, and stem cells. They could help prevent icing on aircraft wings, wind turbines, bridge cables, and more, and even help us create clouds.

Perspective Shift

The potential ecological advantages of ice nucleators regarding precipitation and cloud formation are tremendous but poorly understood, as Meister and Molinero discuss in the study. They say there is a “significant gap in our understanding of the relationship between climate and life.” Hopefully, learning more about ice nucleators will help us close that gap.

That line struck me, though — particularly the “understanding of the relationship between climate and life” bit. I realized when I read that I had never considered life’s impact on nature before. I mean, clearly, the climate impacts life, and we humans are creating this round of global warming. But I never woulda thought microscopic organisms help make ice sooner than water would without them.

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Photo by Osman Rana on Unsplash