An aquatic creature tardigrade can survive without water for decades - here's how

How do they survive dehydration?
Nergis Firtina
A tardigrade in space
A tardigrade in space

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Tardigrades, also known as the water bears, were known to survive in harsh conditions. In addition, recent research led by The University of Tokyo scientists suggests that tardigrades can also survive even when they are dehydrated.

It means, they can live without water.

The research was published in PLOS Biology on September 6.

As suggested, the scientists examined the gel proteins that tardigrades produce as a result of dehydration. Consequently, the study revealed how tardigrades use DNA clouds and fluorescent shields to protect themselves from different kinds of radiation.

“Although water is essential to all life we know of, some tardigrades can live without it potentially for decades. The trick is in how their cells deal with this stress during the process of dehydration,” said Associate Professor Takekazu Kunieda from the University of Tokyo’s Department of Biological Sciences.

An aquatic creature tardigrade can survive without water for decades - here's how
Tardigrade captured by electron microscope

“It’s thought that as water leaves a cell, some kind of protein must help the cell maintain physical strength to avoid collapsing in on itself. After testing several different kinds, we have found that cytoplasmic-abundant heat soluble (CAHS) proteins, unique to tardigrades, are responsible for protecting their cells against dehydration.”

How is that possible?

According to CAHS proteins, when the cell in which they are contained becomes dehydrated, that's when they start acting. Upon drying, CAHS proteins produce filaments that resemble gels.

Due to the reversibility of the process, the filaments gradually disappear when the tardigrade cells rehydrate at a rate that doesn't put the cell under undue strain. Interestingly, the proteins continued to work in the same manner even after being removed from tardigrade cells.

“Trying to see how CAHS proteins behaved in insect and human cells presented some interesting challenges,” said lead author Akihiro Tanaka, a graduate student in the lab.

“For one thing, in order to visualize the proteins, we needed to stain them, so they show up under our microscopes. However, the typical staining method requires solutions containing water, which obviously confounds any experiment where water concentration is a factor one seeks to control. So we turned to a methanol-based solution to get around this problem.”

"Everything about tardigrades is fascinating"

"The extreme range of environments some species can survive leads us to explore never-before-seen mechanisms and structures. For a biologist, this field is a gold mine,” said Kunieda.

“Everything about tardigrades is fascinating" also added.

More than 300 other protein subtypes will be sorted through by Kunieda and his team, some of which probably contribute to the remarkable capacity for life preservation of these little water bears.

Abstract

Tardigrades are able to tolerate almost complete dehydration by entering a reversible ametabolic state called anhydrobiosis and resume their animation upon rehydration. Dehydrated tardigrades are exceptionally stable and withstand various physical extremes. Although trehalose and late embryogenesis abundant (LEA) proteins have been extensively studied as potent protectants against dehydration in other anhydrobiotic organisms, tardigrades produce high amounts of tardigrade-unique protective proteins. Cytoplasmic-abundant heat-soluble (CAHS) proteins are uniquely invented in the lineage of eutardigrades, a major class of the phylum Tardigrada and are essential for their anhydrobiotic survival. However, the precise mechanisms of their action in this protective role are not fully understood. In the present study, we first postulated the presence of tolerance proteins that form protective condensates via phase separation in a stress-dependent manner and searched for tardigrade proteins that reversibly form condensates upon dehydration-like stress. Through a comprehensive search using a desolvating agent, trifluoroethanol (TFE), we identified 336 proteins, collectively dubbed “TFE-Dependent ReversiblY condensing Proteins (T-DRYPs).” Unexpectedly, we rediscovered CAHS proteins as highly enriched in T-DRYPs, 3 of which were major components of T-DRYPs. We revealed that these CAHS proteins reversibly polymerize into many cytoskeleton-like filaments depending on hyperosmotic stress in cultured cells and undergo reversible gel-transition in vitro. Furthermore, CAHS proteins increased cell stiffness in a hyperosmotic stress-dependent manner and counteract the cell shrinkage caused by osmotic pressure, and even improved the survival against hyperosmotic stress. The conserved putative helical C-terminal region is necessary and sufficient for filament formation by CAHS proteins, and mutations disrupting the secondary structure of this region impaired both the filament formation and the gel transition. On the basis of these results, we propose that CAHS proteins are novel cytoskeleton-like proteins that form filamentous networks and undergo gel-transition in a stress-dependent manner to provide on-demand physical stabilization of cell integrity against deformative forces during dehydration and could contribute to the exceptional physical stability in a dehydrated state.

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