What makes a tardigrade so tough?

This week, I’ve taken the decision to shrink myself down and jump into a pond. Because I want to get up close and personal with perhaps the toughest group of critters in the animal kingdom: tardigrades.

The tardigrade can grow to around half a millimetre and usually lives on a diet of algae, small invertebrates, and smaller tardigrades. A single litre of water can contain as many as 25000 of them, and they are found pretty much everywhere. These organisms, sometimes referred to as ‘Water Bears’ or ‘Moss Piglets’ were first discovered in 1773 by German scientist Johann Goeze. In 1777, Italian scientist Lazzaro Spallanzani gave them the name ‘Tardigrada,’ which translates to ‘slow-stepper.’ Me neither.

Anyway, most people haven’t heard of tardigrades because of their ‘slow steps’. They know them for being one of the toughest little guys out there.

Let’s quickly run through the accolade list, for those that aren’t aware.

Tardigrades can survive 150 degrees celsius, which is about the same temperature as the surface of Mercury.

They can survive 0.05 Kelvin, a whisker away from absolute Zero. And longer term, they can survive -20 degrees Celsius for about 30 years.

The average Tardigrade can survive pressures of 1200 atmospheres. Some can survive 6000 atmos, which is roughly 6 times the pressure of the lowest point of the Mariana Trench.

Gamma rays are produced in the most energetic parts of the universe, such as stars and supernovae. Humans have harnessed the energy of gamma rays in the medical field in order to sterilise equipment. Gamma rays are very good at killing things. A dose of 5-10 gray, the unit of absorbed ionizing radiation, could be fatal to a human. A tardigrade can withstand over 5200 of them.

Quick side note, tardigrades cannot be considered extremophiles, as an extremophile is an organism that actively chooses to live in a harsh environment. Given the choice, a tardigrade would happily curl up on a wet bog and venture nowhere near a volcanic spring. In the same way that, if needs be, I could do upwards of 5 press ups. But if you asked me to, I would jump in a volcanic spring.

Either way, this is evolutionary overkill. So, how do they do it? Well, I’m really sorry to do this to you, but we’re going to have to talk about some… chemistry.

The answer mostly comes down to retain their cell structure. The main problem with extremes of temperature or pressure or radiation is that it affects the amount of water you can keep in a cell. Water is vital to nearly all the reactions that go on inside cells, as well as retaining its structure. The cell dries out, cell functions stop, it’s bad news all round.

Intrinsically disordered proteins, named after my sleep schedule, are proteins that do not exist in one fixed three-dimensional shape. When the water concentration drops, tardigrades start to produce IDPs, or already have some ready depending on the species. As each cell desiccates, the IDPs inside them form amorphous solids. The IDPs then become a glass like structure which maintains the shape of the cell without the need for water, like those planks of wood that stop a cave from collapsing.

The tardigrade actually protects itself against drying out on two fronts. Not only does it utilise IDPs, but also employs the services of damage suppressors proteins, or DSUPs. DSUPs are exclusive to tardigrades, and prevent the breakdown of the DNA helices in cells. If a cell's DNA can remain intact, it can continue to code for IDPs and the cells can stay relatively functional, not unlike my sleep schedule.

So that’s the tardigrade: tiny, tough, and terrific. I’d wish them luck, but they don’t need it.