Phylum Tardigrada: The Indestructible “water bears”?

Mayukh Sinha, Amity University Kolkata

The planet Earth could be home to amazing species. No doubt, Human Beings are the best kind of life on earth. However, on thorough observation, incredible things come up.

We are talking about the Phylum Tardigrada. Tardigrades are microscopic creatures that are maximum of 1 mm in size but usually are found to be about half that size. These are creatures that appear as “water bears” with eight puffy legs and claws like those of Brown Bears and are mostly found in moist lichen, moss, or leaf litter.

They can live for 100 years, withstand extreme temperatures as low as -200°C (-328°F) and as high as 151°C (304°F). They can survive under extreme pressure as high as 87,000 pounds (i.e. 6 times what you would experience at the underside of the sea). An experiment conducted by a group of Tardigrade researchers inferred some groundbreaking results. When a precise genome analysis was conducted on a species of Tardigrade Ramazzottius varieornatus, it seemed that it can tolerate direct exposure to low humidity and is also capable of withstanding extremes in the dehydrated condition.

In addition to that, it can also tolerate a heavy dosage of radiation. Another example is Hypsibius dujardini, which is capable of surviving in the toughest of the conditions. Now, a catch with H.dujardini is that it cannot tolerate low humidity until and unless it gets a longer time of pre-exposure to a highly humid environment. They are proof against space traveling (i.e. direct solar radiation, Gamma-rays, and X-rays) and, they’re the “Toughest Organism” known till now.

Phylum Tardigrada: How do they do it?

The answer is Cryptobiosis. Let us talk in simple terms. We are talking about the facility or superpower that they possess in their body to sustain in extreme conditions. After they sense the acute conditions in their environment, they initiate the mentioned process i.e. Cryptobiosis by turning themselves into a little ball-like structure termed as Tun. Some superpowers as you’ll say;

• Surviving in the environment with a lack of water by Anhydrobiosis.
• Surviving extreme low temperatures and not forming into ice crystals by Cryobiosis.
• Extremely saline conditions by Osmobiosis.
•  No Oxygen? No problem- Anoxybiosis.

There are more superpowers that they will use for survival. The interesting fact comes now. Once they are in their cryptobiotic stage, the elixir is simply water. Take the Tardigrade and put it in a Petri plate of water. Yes, they’ll be crawling again!

 Now, the most probable answer behind their superpower to tolerate radiation is the Dsup (Damage suppressor) protein. It has been hypothesized that Dsup protein may have an affinity for DNA. And probably this might be the reason for the DNA Repair/Protection under irradiation.

After a successful experiment on human cultured cells, it has been inferred that the combination of NAC (N-acetyl-L-cysteine) and Dsup protein led to greater suppression of DNA Damage SSBs (Single-Stranded Breaks)caused by Oxidative Stress. When Dsup has incorporated alone in DSBs (Double-Stranded Breaks), it was shown a reduction of ~40% in DNA Fragmentation. It’s a long way to go now. The search has already begun.

Now, the question is;

PhylumTardigrada Indestructible?

Well, According to Sandra J. Mclnnes, Tardigrades are resistant to radiation and able to repair their DNA, which makes them resilient to it.  However, she also cautioned that the Tardigrades are invincible, but they are mortal.

Sources:

1. Tardigrades in Space Research-Past and Future, Erdmann Weronika and Kaczmarek Łukasz, 2016 Oct 20, Orig Life Evol Biosph. 2017; 47(4): 545-553, http://dx.doi.org/10.1007%2Fs11084-016-9522-1

2. Global diversity of tardigrades (Phylum Tardigrada) in freshwater, James R. Garey and Sandra J. Mclnnes and Phillip Brent Nichols, April 2008, Hydrobiologia 595(1):101-106, http://dx.doi.org/10.1007/978-1-4020 8259-7_12

3. Extremotolerant tardigrade genome and improved radiotolerance of human cultured cells by tardigrade- unique protein, Takuma Hashimoto, Daiki D. Horikawa, Yuki Saito, Hirokazu Kuwahara, Hiroko Kozuka-Hata, Tadasu Shin-I, Yohei Minakuchi, Kazuko Ohishi, Ayuko Motoyama, Tomoyuki Aizu, Atsushi Enomoto, Koyuki Kondo, Sae Tanaka, Yuichiro Hara, Shigeyuki Koshikawa, Hiroshi Sagara, Toru Miura, Shin-ichi Yokobori, Kiyoshi Miyagawa, Yutaka Suzuki, Takeo Kubo, Masaaki Oyama, Yuji Kohara, Asao Fujiyama, Kazuharu Arakawa, Toshiaki Katayama, Atsushi Toyoda & Takekazu Kunieda, 20 September 2016, Nat Commun 7, 12808(2016), http://doi.org/10.1038/ncomms12808

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