Cryptobiosis or anabiosis is a metabolic state in extremophilic organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency.
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 (Polypedilum vanderplanki).
[4] In some creatures, such as bdelloid rotifers, no trehalose has been found, which has led scientists to propose other mechanisms of anhydrobiosis, possibly involving intrinsically disordered proteins.
[5] In 2011, Caenorhabditis elegans, a nematode that is also one of the best-studied model organisms, was shown to undergo anhydrobiosis in the dauer larva stage.
[6] Further research taking advantage of genetic and biochemical tools available for this organism revealed that in addition to trehalose biosynthesis, a set of other functional pathways is involved in anhydrobiosis at the molecular level.
[11][12] In situations lacking oxygen (a.k.a., anoxia), many cryptobionts (such as M. tardigradum) take in water and become turgid and immobile, but can survive for prolonged periods of time.
Some ectothermic vertebrates and some invertebrates, such as brine shrimps,[13] copepods,[14] nematodes,[15] and sponge gemmules,[16] are capable of surviving in a seemingly inactive state during anoxic conditions for months to decades.
However, there is evidence that the stress-induced protein p26 may act as a protein chaperone that requires no energy in cystic Artemia franciscana (sea monkey) embryos, and most likely an extremely specialized and slow guanine polynucleotide pathway continues to provide metabolic free energy to the A. franciscana embryos during anoxic conditions.
Organisms capable of enduring these conditions typically feature molecules that facilitate freezing of water in preferential locations while also prohibiting the growth of large ice crystals that could otherwise damage cells.