Secrets of suspended metabolism in indestructible invertebrates

The molecular components of a group of invertebrates known as tardigrades have been studied by SERS, showing changes that occur when the creatures go into a state of suspended metabolism to survive extreme conditions. Tardigrades, also known as water bears, are minute invertebrates up to 1.2 mm long that can exist in extreme environments, from deep seas to high mountains.

Although they are very small, they have evolved a way to survive harsh conditions. They can tolerate temperatures of up to 151°C or –272°C for a few minutes, as well as lethal doses of gamma rays. Some have even survived the vacuum in outer space. They do this by entering a temporary, stress-tolerant state known as cryptobiosis but the mechanism behind this change is unclear.

Now, European scientists have found a way to explore the state of suspended metabolism using surface-enhanced Raman spectroscopy (SERS) which allows living tardigrades to be examined, as described in the Journal of Biophotonics. Two species of tardigrades were collected from moss samples and they were coated with gold and silver nanoparticles for laser irradiation.

The resulting spectra displayed many features which were attributed to proteins, lipids and nucleotides, as well as individual amino acids like tyrosine and phenylalanine. The two species gave different spectra which allows their differentiation. Moreover, the spectra of tardigrades under cryptobiosis, induced by dessication, were also different to those in the wet state. The phenylalanine band disappeared, proteins bands were altered and signals due to nucleotides and adenine became stronger.

The method should allow the molecular mechanisms associated with cryptobiosis to be studied in live tardigrades and the results will broaden our knowledge of ways to preserve and stabilise these and other life forms.

Image: William Miller, Tardigrade Reference Center