Tardigrades: Water bears in space

“Tardigrades can be found all over the world from the Arctic to the Antarctic, from high mountains to deserts, in urban areas and backyard gardens,” he explained.

“In terrestrial environments, they always require at least a film of water surrounding their bodies to perform activities necessary for life.”

But if these conditions change, tardigrades are capable of entering an extreme form of resting called cryptobiosis.

In this state, they are capable of withstanding freezing, a process called cryobiosis, and desiccation, a process called anhydrobiosis.

Arid state

“This capability [to withstand desiccation] involves a complex array of factors working at molecular, physiological and structural levels,” Professor Guidetti told BBC News.

“The physiology and biochemistry of anhydrobiosis is bound to a complex system that involves many different molecular components working together as bioprotectants.”

Sugars and heat stress proteins, which are expressed when cells become stressed, act as “molecular chaperones” protecting important molecules within the cell.

The disaccharide sugar called trehalose plays a role in the protection of cells and biomolecules from dehydration by replacing water that is normally bonded to hydrogen.

During dehydration, loss of water increases the ionic concentration leading to the formation of reactive oxygen species (ROS) which damage important biomolecules including DNA.

To counter this attack, organisms produce antioxidants that can mop up ROS minimising cell damage.

The regulation of antioxidant metabolism represents a crucial strategy to avoid damage during dehydration.

“Tardigrades can persist for months, or even for years, in the anhydrobiotic state. When in the desiccated state, tardigrades show a high resistance to physical and chemical extremes,” explains Professor Guidetti.

“For example, very low and high temperatures, exposure to high pressure or vacuum, as well as contact with organic solvents and ionising radiation.”

Exposure to the conditions found in space induces rapid changes in living systems.

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