Cryptobiosis Protects From Extremes

Biological Strategy

Water bears

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Protect From Nuclear Radiation

Nuclear radiation is a threat that some living systems can survive. Most survival strategies help living systems survive other kinds of extreme threats, although in situations where there has been human-caused exposure to nuclear radiation, some quickly reproducing organisms (such as bacteria) might develop new strategies. The tardigrade (also called a water bear) survives extreme conditions by undergoing a suspended metabolic state called cryptobiosis. Going into this state helps it survive nuclear radiation, dehydration, and low temperatures.

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Protect From Chemicals

Chemicals are everywhere in the bodies of living organisms and their external environments. While most chemicals are valuable or benign, some are toxic, including those used for defense (such as the mucus that protects clownfish from an anemone’s stinging tentacles). Even naturally-occurring chemicals, such as arsenic, must be managed to reduce their impact. Some living systems have strategies to break down harmful chemicals, alter them into less toxic forms, physically prevent chemicals from harming sensitive tissues, and more. For example, some herbivorous mammals can digest toxic compounds in plants because they have a particular enzyme that helps them process poisonous plant compounds.

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Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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The waterbear survives extreme environmental conditions by entering a reversibly suspended metabolic state known as cryptobiosis.

Introduction

The tardigrade, also known as the waterbear, is a microscopic invertebrate with a remarkable capacity for survival in some of Earth’s harshest environments. Found in habitats ranging from freshwater to high mountains and polar regions, these tiny creatures can endure extreme conditions by entering a unique state of suspended animation called cryptobiosis. This extraordinary allows tardigrades to effectively halt metabolic processes and survive in conditions where water is scarce or temperatures are extreme—conditions that would be fatal for most organisms.

The Strategy

To survive challenging conditions like dehydration or extreme temperature shifts, tardigrades enter cryptobiosis, where they effectively suspend their metabolic activity. The most studied form of cryptobiosis in tardigrades is anhydrobiosis, which helps them withstand desiccation. In this process, the tardigrade retracts into a compact, desiccated form called a “tun,” shedding over 95% of its body water. This state is more than just a physical change; it is supported by specific biochemical adaptations that protect the tardigrade’s cells during desiccation.

Video

One of the critical elements of this protection is the production of tardigrade-specific proteins called CAHS (cytoplasmic abundant heat-soluble) proteins. CAHS proteins are intrinsically disordered, meaning they do not maintain a fixed structure. This flexibility allows them to form a protective network around essential cellular components during desiccation. CAHS proteins work in synergy with trehalose, a sugar that is widely used by desiccation-tolerant organisms but present in low levels in tardigrades. This combination—CAHS proteins and trehalose—stabilizes cellular structures in a unique way, creating a robust, protective environment that minimizes damage during dehydration. This partnership is essential for maintaining the structural integrity of tardigrade cells when water is nearly absent. When environmental conditions improve, the tardigrade rehydrates, and its metabolic functions resume, enabling the organism to reanimate and continue its life cycle.

Tardigrade is starting to dehydrate with a sugar solution, trehalose, thickening as water is
lost. This protects the tardigrade's cells from damage until moisture conditions improve.

The Potential

The tardigrade’s cryptobiosis strategy offers fascinating insights for resilience to extreme dehydration. In biomedical preservation, for example, this mechanism could inspire ways to stabilize cells, tissues, or biomolecules under dry storage conditions. Agricultural and food storage solutions might also benefit from applying this strategy, enabling enhanced desiccation tolerance in crops or longer shelf lives for perishable products. Further, understanding the specific interactions between CAHS proteins and trehalose could lead to synthetic materials or additives that mimic the tardigrade’s protective matrix, providing enhanced stability for biological materials and pharmaceuticals in dehydrated environments.

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References

A long-term goal of the desiccation tolerance field is to understand better how to confer anhydrobiotic abilities to organisms that do not naturally survive drying. This study and its findings provide a compelling argument that to do so may require the combination of different, synergistic, protectants. This point is highlighted by our yeast desiccation assays (Fig. 5) where CAHS proteins confer little protection when heterologously expressed alone but provide dramatically increased protection in the presence of trehalose. Further understanding the mechanistic basis of CAHS-trehalose synergy will help to build a foundation for pursuing the long-term goal of engineering desiccation tolerance into organisms for the purposes of crop development and food security.

Journal article

Trehalose and tardigrade CAHS proteins work synergistically to promote desiccation tolerance

Communications Biology | October 1, 2022 | Kenny Nguyen, Shraddha KC, Tyler Gonzalez, Hugo Tapia & Thomas C. Boothby

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Reference

“Most incredible of all, however, is the virtually indestructible nature of tardigrades while they remain in cryptobiosis. In laboratory experiments, cryptobiotic specimens have been chilled in liquid helium to -457°F (-272°C), which is only marginally above absolute zero. They have also been heated to temperatures exceeding 300°F (149°C), exposed to radiation doses far in excess of the lethal dose for humans, immersed in vats of liquid nitrogen, concentrated carbolic acid, hydrogen sulphide, brine, and pure alcohol, and even bombarded by deadly streams of electrons inside an electron microscope. Yet when removed from all of these incredibly hostile environments – which would have proven fatal for any other form of animal life – and moistened with water, these astounding creatures recovered.

They simply emerge from their cryptobiotic state, rehydrate themselves, and amble away on their four pairs of stubby claw-tipped legs, completely unharmed.” (Shuker 2001:113)

Book

The Hidden Powers of Animals: Uncovering the Secrets of Nature

01/01/1970 | Dr. Karl P. N. Shuker

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Reference

“…Tardigrades are known to enter cryptobiosis at any stage of their life cycle, from egg to adult. Cryptobiosis has to be considered a form of quiescence, being directly induced and maintained by the occurrence of adverse conditions for an active life, and promptly broken once the adverse conditions are removed…In tardigrades, there are several forms of cryptobiosis: anhydrobiosis, cryobiosis, anoxybiosis and osmobiosis. Anhydrobiosis is the most studied. Entering anhydrobiosis, tardigrades contract their body into a so-called tun, loosing most of their free and bound water (>95%), synthesizing cell protectants (e.g., trehalose, glycerol, heat shock proteins…and strongly reducing or suspending their metabolism…” (Bertolani et al. 2004:16)

Journal article

Experiences with dormancy in tardigrades

J Limnol | 20/01/2012 | Roberto BERTOLANI, Roberto GUIDETTI, Ingemar K. JÖNSSON, Tiziana ALTIERO, Deborah BOSCHINI, Lorena REBECCHI

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Reference

“…[T]ardigrade-specific intrinsically disordered proteins (TDPs) are essential for desiccation tolerance. TDP genes are constitutively expressed at high levels or induced during desiccation in multiple tardigrade species…TDPs form non-crystalline amorphous solids (vitrify) upon desiccation, and this vitrified state mirrors their protective capabilities.” (Boothby et al. 2017:975)

Journal article

Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation

Molecular Cell | 16/03/2017 | Boothby TC; Tapia H; Brozena AH; Piszkiewicz S; Smith AE; Giovannini I; Rebecchi R; Pielak GJ; Koshland D; Goldstein B

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Reference

Magazine article

How the Remarkable Tardigrade Springs Back to Life after Drying Out

Smithsonian Magazine | 20/03/2017 | Daley J

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