How some organisms exploit cryptobiosis to live for thousands of years

Organisms capable of cryptobiosis are called cryptobionts

by Lorenzo Ciotti
How some organisms exploit cryptobiosis to live for thousands of years

In the cryptobiotic state, all metabolic processes stop, preventing reproduction, development and repair. An organism in a cryptobiotic state can essentially live indefinitely until environmental conditions become hospitable again.

When this occurs, the organism will return to its pre-cryptobiosis metabolic state of life. In fact, cryptobiosis is an ametabolic state of life which some simple organisms enter in response to adverse environmental conditions, such as drying, freezing, and lack of oxygen.

Organisms capable of cryptobiosis are called cryptobionts. A typical example of cryptobiosis occurs in the crustacean Artemia salina. The desiccation of the saline pools in which it lives is overcome thanks to the deposition of long-lasting eggs, capable of remaining in a state of quiescence for long periods until favorable conditions for their development reappear.

Tardigrades placed in adverse conditions develop a series of defensive mechanisms ranging from incistidation to the suspension of any visible metabolic activity. In conditions of dehydration they retract their paws and encapsulate themselves inside the cuticle, which undergoes chemical transformations, becoming waterproof.

In the case of low temperatures, ice crystals with controlled growth form in the liquid that fills the hemocoel. In both cases, an important function is performed by the synthesis of trehalose, a disaccharide sugar which forms a gel with water and other cellular substances which allows the organelles to be preserved until the next eventual rehydration.

Anhydrobiosis is the most studied form of cryptobiosis and occurs in situations of extreme desiccation. The term anhydrobiosis derives from the Greek for life without water and is most commonly used for the desiccation tolerance observed in certain invertebrate animals such as bdelloid rotifers, tardigrades, brine shrimp, nematodes, and at least one insect, a species of chironomid.

However, other life forms exhibit desiccation tolerance. These include the resurrection plant Craterostigma plantagineum, the majority of plant seeds, and many microorganisms such as bakers' yeast. Studies have shown that some anhydrobiotic organisms can survive for decades, even centuries, in the dry state.

Some ectothermic vertebrates and some invertebrates, such as brine shrimps, copepods, nematodes, and sponge gemmules, are capable of surviving in a seemingly inactive state during anoxic conditions for months to decades.

Studies of the metabolic activity of these idling organisms during anoxia have been mostly inconclusive. This is because it is difficult to measure very small degrees of metabolic activity reliably enough to prove a cryptobiotic state rather than ordinary metabolic rate depression.