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As global temperatures rise, scientists are turning to an unexpected source—the same yeast that makes bread rise and beer fizz—to uncover what allows some lifeforms to survive extreme heat while others cannot.

In a published in Molecular Biology and Evolution, University of Rochester biologist Justin Fay and his colleagues compared two closely related species of yeast to understand how organisms cope with heat and why some species manage it better than others.

Proteins—the molecules responsible for most of a cell's essential tasks—are especially sensitive to heat, and if they lose their shape, cells can fail. The researchers found that survival depends not only on how sturdy proteins are but also on the cellular environment that supports them. These insights could reshape how we think about evolution, disease, and life in a warming world.

"We studied yeast, but the findings are likely broadly relevant because mechanisms of protein stability are shared across many organisms," says Fay, a professor in the Department of Biology.

"These insights are also important for understanding evolution and how human pathogens evolve, since growth at body temperature requires similar adaptations."

The proteins behind heat resistance

The researchers compared Saccharomyces cerevisiae (commonly known as baker's or brewer's yeast) and Saccharomyces uvarum. Although these two yeast species are closely related, Saccharomyces cerevisiae can tolerate heat about 8 degrees Celsius (14.4 degrees Fahrenheit) better than Saccharomyces uvarum—a considerable difference in microbial terms.

Fay and his colleagues used a technique called thermal proteomic profiling, which involves treating proteins with heat and measuring which proteins remain soluble (folded). They found that 85% of the proteins in Saccharomyces cerevisiae were more heat-stable than their counterparts in Saccharomyces uvarum.

How cells give proteins an assist

However, the researchers found that protein design wasn't the only factor contributing to an organism's heat tolerance. The team created a hybrid yeast with genetic material from both Saccharomyces cerevisiae and Saccharomyces uvarum and discovered that even the more heat-sensitive proteins held up better inside the hybrid cell's heat-friendly environment.

In other words, cells don't leave proteins to fend for themselves; they enlist other molecules, adjust chemical conditions, and use specialized "chaperon proteins" to help proteins keep their shape and function even under heat stress.

The findings suggest that both protein structure and the cellular environment matter for survival, and species may be able to adapt to higher temperatures in more than one way.

"Because the cellular environment is also important, there may be ways in which organisms can evolve some tolerance without changing all their proteins," Fay says.

Mapping adaptation

The work builds on Fay's ongoing research: combining protein-level analysis with genetic approaches to map the step-by-step genetic changes that make heat survival possible; uncover why certain species adapt more easily than others; and identify how these adaptive steps differ between species.

Ultimately, these insights could reveal not only how yeast strains evolve to survive heat but also the broader rules that govern how life adapts—or fails to adapt—to changing environments.