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Cryptobiosis or anabiosis is a metabolic state in extremophilic organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. When environmental conditions return to being hospitable, the organism will return to its metabolism state of life as it was prior to cryptobiosis.
Invertebrates undergoing anhydrobiosis often contract into a smaller shape and some proceed to form a sugar called trehalose, a disaccharide consisting of two molecules of glucose with high water retention capabilities. Desiccation tolerance in plants is associated with the production of another sugar, sucrose. These sugars are thought to protect the organism from desiccation damage. 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.
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. 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. These are mainly defense mechanisms against reactive oxygen species and xenobiotics, expression of heat shock proteins and intrinsically disordered proteins as well as biosynthesis of polyunsaturated fatty acids and polyamines. Some of them are conserved among anhydrobiotic plants and animals, suggesting that anhydrobiotic ability may depend on a set of common mechanisms. Understanding these mechanisms in detail might enable modification of non-anhydrobiotic cells, tissues, organs or even organisms so that they can be preserved in a dried state of suspended animation over long time periods.
As of 2004, such an application of anhydrobiosis is being applied to . In vaccines, the process can produce a dry vaccine that reactivates once it is injected into the body. In theory, dry-vaccine technology could be used on any vaccine, including live vaccines such as the one for measles. It could also potentially be adapted to allow a vaccine's slow release, eliminating the need for Booster dose. This proposes to eliminate the need for refrigerating vaccines, thus making dry vaccines more widely available throughout the developing world where refrigeration, electricity, and proper storage are less accessible.
Based on similar principles, lyopreservation has been developed as a technique for preservation of biological samples at ambient temperatures. Lyopreservation is a biomimetic strategy based on anhydrobiosis to preserve cells at ambient temperatures. It has been explored as an alternative technique for cryopreservation. The technique has the advantages of being able to preserve biological samples at ambient temperatures, without the need for refrigeration or use of cryogenic temperatures.Yang G, Gilstrap K, Zhang A, Xu LX, He X. "Collapse temperature of solutions important for lyopreservation of living cells at ambient temperatures." Biotechnol Bioeng. 2010 Jun 1;106(2):247–259.Chakraborty N, Chang A, Elmoazzen H, Menze MA, Hand SC, Toner M. "A spin-drying technique for lyopreservation of mammalian cells". Ann Biomed Eng. 2011 May;39(5):1582–1591.
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 (MRD). Many experts are skeptical of the biological feasibility of anoxybiosis, as the organism is managing to prevent damage to its cellular structures from the environmental negative free energy, despite being both surrounded by plenty of water and thermal energy and without using any free energy of its own. However, there is evidence that the stress-induced protein p26 may act as a protein chaperone that requires no energy in cystic Brine shrimp (Sea-Monkeys) 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. It seems that A. franciscana approaches but does not reach true anoxybiosis.
The tardigrade, or water bear, can undergo all five types of cryptobiosis. While in a cryptobiotic state, its metabolism reduces to less than 0.01% of what is normal, and its water content can drop to 1% of normal.Ross Piper (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press. It can withstand extreme temperature, radiation, and pressure while in a cryptobiotic state.Illinois Wesleyan University Tardigrade Facts
Some and can also undergo cryptobiosis.
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