Water bears, also known as tardigrades, are microscopic invertebrates that are able to survive in extreme conditions through a process called cryptobiosis. They can withdraw their limbs and form a protective covering called a tun when drying out to enter a dormant state where their metabolism drops drastically. In this state they can survive being heated, frozen, subjected to radiation levels 1000 times lethal for humans, and complete desiccation where they lose nearly all their body water. They are able to revive after these conditions through a disaccharide sugar called trehalose that replaces lost water and prevents cellular damage upon rehydration. Tardigrades were able to survive exposure to the vacuum of space and solar radiation during a 2007 mission,

1. Water Bears Shelby Loder

2. About Water Bears Invertebrate Belong to Tardigrada Open circulatory system Grow up to 1.5mm Have four pairs of limbs, short plump bodies, and a pair of stylets Commonly found in marine, fresh water, and semi-aquatic terrestrial environments, but also found in the deep sea to the highest mountains Surrounded by a film of water (when active) Feed on fluids of plant cells animals cells, and bacteria Prey to amoebas, nematodes, and other tardigrades

3. Latent States Cryptobiosis- Reversible metabolic suspension Anhydrobiosis- Severe dehydration (Most studied state) Cryobiosis- Freezing temperatures Osmobiosis- Increased salinity Anoxybiosis- Lack of oxygen Encystment- Dormant state Can go through any of these during any stage of their life span In these states tardigrades have been known to survive: Temperatures as low as -328ºF and as high as 304 ºF Freezing and thawing processes Changes in salinity Levels of x-ray radiation that are 1000x the lethal human dose Some harmful chemicals Boiling alcohol Low pressure of a vacuum High pressure (Up to 6x the pressure of the deepest part of the ocean) Can extend life-span of a tardigrade from a few months up to several years possibly over a century. Active life-span is not effected (Estimated 3-30 months)

4. Anhydrobiosis During extreme dryness, Water Bears pull their head and legs inward, reducing surface area to reduce water loss, longitudinally contract their body, and form a cuticular wall around its body. This ball is called a Tun and is vital for successful anhydrobiosis If organism dries out too quickly the body collapses and does not revive upon rehydration. Hence, relative humidity must be around 70-95% for successful tun formation Metabolism drops to 0.01% of normal and their water content can drop to 1% of normal

5. Anhydrobiosis The state of dehydration includes the loss of: Free water found in aqueous solutions of the body Bound water maintains the structure of vital hydrated macromolecules (proteins, membrane phospholipids, and nucleic acids) Destruction of these macromolecules would cause irreversible damage as a result of anhydrobiotic failure How do they maintain structural integrity while removing all their water?

6. Trehalose Trehalose a disaccharide sugar is produced to provide protection and replace bound water Acts like sugar that is heated when making hard candy Is not susceptible oxidation, like most sugars, when in contact with air which prevents reactions with proteins When water is absorbed (when reviving), trehalose prevents the membrane from becoming liquid and loosing cell contents, instead trehalose makes it a gel-like state

7. In the anhydrobiotic state Can survive extreme conditions that are not able to survive in the active life such as: Sub-zero temperatures, high radiation, high temperatures, and vacuums at lethal levels if they were active The metabolism ceases and is resumed only when the environmental conditions allow rehydration Suspend life during desiccation and does not age during anhydrobiosis Have been revived after over 100 years of being in this state Revival takes a few hours, depending on how long they were in the cryptobiotic state

8. Space Exploration Foton-M3 mission by ESA on September 14, 2007 Twelve day mission Low Earth orbit (270 km) unprotected Space vacuum (0.00001 Pa vs. 100000 Pa on Earth) Residual water well below 1% mass (normally 85% of their weight) Radiation of more than 7,000 kJm -2 (more than 1,000 times greater than on Earth’s surface) Only a few of them survived exposure to full range of ultraviolet rays and vacuum A few of them became the first animals to return alive after exposure to both space vacuum and solar radiation

9. Loupe magnification (10x) Tun of Milnesium tardigradum on salt residue from water Magnification (100x)