Tardigrades Don't Survive Drying Out the Way We Thought

For decades the textbook answer was trehalose. The little eight-legged "water bears" can lose 99% of their body water and come back to life years later, and the sugar trehalose was supposed to be the protective glass that held their cell machinery in place. It works that way in brine shrimp and yeast.

Then people actually measured tardigrade trehalose. Some species accumulate it in bulk during desiccation. Others — including Milnesium tardigradum, one of the most desiccation-tolerant species ever tested — produce only trace amounts and survive just as well. The sugar story didn't add up.

What does the work is a class of proteins that doesn't exist outside this phylum. They're called tardigrade-specific intrinsically disordered proteins (TDPs), and unlike normal proteins they have no fixed 3D shape in solution. As a tardigrade dries, the TDPs vitrify around its ribosomes, DNA, and membranes — forming a glass-like solid that pins everything in place without crystallizing. Rehydrate the animal and the glass dissolves.

The trehalose isn't useless. It seems to help maintain the glassy state in the species that bother making it. But the load-bearing trick is a protein family that evolved once, in tardigrades, and turns the cytoplasm into amber on demand.