Researchers have found “a new upper temperature limit” for a eukaryote; an amoeba from Lassen Volcanic National Park in California that divides at temperatures up to 63°C (145°F). The prior record was 60°C.
(Note there is a bacteria that can grow at 100°C, but this is still impressive!)
Most of this paper is devoted to figuring out *how* these cells are able to live at high temperatures. Interestingly, the scientists mostly used computation + ML tools to do that; there’s relatively little in the way of wet-lab experiments, perhaps because these cells are so difficult to grow.
For example, they did RNA sequencing, pulled out the 500 most abundant transcripts, and then used AlphaFold2 to predict the protein structures. These proteins had fewer hydrophobic amino acids on the outsides of their proteins compared to other eukaryotes, which may make it harder for heat to cause protein clumping.
(A folded protein usually hides hydrophobic amino acids inside, away from water. But heat makes partial unfolding more likely, thus exposing those patches. These exposed patches of hydrophobic regions can then stick together, causing a big clump of protein. This is what happens when you cook egg whites too hot.)
In another experiment, they used a ML model, TemBERTure (which is a great name) to predict the protein melting temperatures for these predicted structures, and found that, indeed, the proteins were predicted to remain folded at much higher temperatures than other eukaryotes.
Aside from proteins, the amoebas also upregulated genes involved in protein maintenance (like proteasomes), and genes involved in DNA repair, etc. Lots of obvious things there.
It's interesting to think about what you can find with simple culturing of organisms from weird places + RNA-seq + tons of computational analysis. It also makes me think about what the theoretical upper limit for eukaryotes might actually be, and why (exactly) they cannot withstand the same extremes as bacteria. These questions might seem simplistic, but many great discoveries in biophysics have come from pondering such "theoretical limits."