How Pompeii worms take the heat

This is the Pompeii worm (Alvinella pompejana), and it is a record-holding animal.

Its record is not for the most unlikely animal (though you have to admit, it is a bit odd looking). You are looking at the animal that is able to withstand higher temperatures than anything else in the animal kingdom. The Pompeii worm routinely withstands scalding 80°C water. Not only that, it can routinely go outside of that to water that is more like room temperature, at 20°C.

That this worm is able to take high temperatures makes sense when you consider where these animals live. These are one of the deep sea vent animals that live near water hot enough to melt lead. As I described recently, the animals themselves don’t venture into the superheated water, but stray close enough that temperature is a consideration for them. And when they move away from the water erupting from the bottom of the ocean floor, they can face temperatures that are only a few degrees above freezing.

Most organisms cannot go into temperatures that high, because their proteins, including all the vital enzymes that catalyze almost every reaction in every cell, should be coming apart at the seams. Proteins are long, strand-like molecules, and they work because that strand is folded into complicated shapes. Those shapes are held together by a whole bunch of complex chemical bonds. But high temperatures can break chemical bonds. You see this process in action every time you cook an egg: the high temperatures break the chemical bonds holding the proteins in their particular shapes, and you get new shapes with different properties. This is why eggs go from runny and clear to more solid and white.

A new paper, authored by Jollivet and team, tries to work out just how the proteins in the Pompeii worm are able to hold together in conditions that would turn ours all sproggly (that's the technical term). They do this by a lot of molecular biology to look at the structure of the proteins in the worms en masse. They note two things.

First, the proteins in the Pompeii worm do not like to dissolve in water (hydrophobic). I don’t pretend to exactly understand how that stabilizes the protein, but it seems to be a trend that is also seen in bacteria that thrive in hot springs and the like.

Second, the proteins in the Pompeii worm have a lot of ionized bits. This made a little more intuitive sense to me, as I could imagine how having lots of positive and negative charges in the proteins would allow for the formation of more ionic bonds (salt bridges) along the length of the protein. More bonds within the protein should mean more stability. Ionic bonds are reasonably strong (weaker than covalent bonds, stronger than hydrogen bonds and Van der Waals forces).

The authors take this analysis one step further, and look not only at the Pompeii worm, but a relative (Paralvinella grasslei; alas, it seems to have no common English name), which is nowhere near as tolerant of those high temperatures. Jollivert and company found that many of the changes they saw were not unique to the Pompeii worm; P. grasslei showed some of the same trends. Both worms seemed to have a trend to hydrophobic proteins compared to other species. The authors suggest that the common ancestor of the two may have been more like the Pompeii worm in liking hot water, and that Paralvinella grasslei migrated back into cooler waters during its evolution.

Hot worm. Cool science.

Reference

Jollivet D, Mary J, Gagnière N, Tanguy A, Fontanillas E, Boutet I, Hourdez S, Segurens B, Weissenbach J, Poch O, Lecompte O. 2012. Proteome adaptation to high temperatures in the ectothermic hydrothermal vent Pompeii worm. PLoS ONE 7(2): e31150. DOI: 10.1371/journal.pone.0031150