Tardigrades are even stranger than they appear

By Susan Linville

Posted December 15, 2023

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Y: Do you remember when we talked about tardigrades, Don?

D: You mean those little animals that can survive dehydration, radiation, and survive in outer space without a space suit?

Y: That's them. Now it appears they are even more unusual than we thought.

D: Yaël, how can they be more unusual?

Y: Researchers have sequenced their genome and found that about one sixth of their genes are from other organisms.

D: Let me guess. They're part bear.

Y: They are called water bears, but no, they are not part bear. Scientists have identified genes from bacteria, plants, fungi, and bacteria-like organisms called Archea.

D: How can that happen? Aren't genes inherited from parents?

Y: The process is called horizontal gene transfer. Along with inheriting genes, they can absorb genes released by other organisms into the environment. The process is very common among bacteria. As a matter of fact, bacteria spread anti-biotic resistance through horizontal transfer of resistance genes.

D: But tardigrades are animals, not bacteria. How can they do that?

Y: Scientists think that when tardigrades are under extreme conditions, such as dryness, their DNA breaks into pieces. When the cells rehydrate, the cell membranes become temporarily leaky, and DNA and other large molecules can pass right through. When the tardigrades repair their own damaged DNA, they stitch the foreign DNA into their own, creating a mixture of genes that come from different species.

D: Too bad humans can't absorb genes.

Y: Humans have foreign DNA too, Don, but not nearly as much as tardigrades. Most of it is from bacteria and viruses.

D: Bacteria and viruses? I'd prefer tiger DNA.

A transparent tardigrade under a microscope

Researchers have sequenced the tardigrade genome and found that about one sixth of their genes are from other organisms. (Philippe Garcelon / flickr)

Have you heard of tardigrades? They're those little animals that can survive dehydration, radiation, and survive in outer space without a space suit.

Now it appears they are even more unusual than we thought.

Researchers have sequenced their genome and found that about one sixth of their genes are from other organisms. Even though they're also called water bears, tardigrades are not part bear. Scientists have identified genes from bacteria, plants, fungi, and bacteria-like organisms called Archea.

How can that happen? Aren't genes inherited from parents?

The process is called horizontal gene transfer. Along with inheriting genes, they can absorb genes released by other organisms into the environment. The process is very common among bacteria. As a matter of fact, bacteria spread anti-biotic resistance through horizontal transfer of resistance genes.

But tardigrades are animals, not bacteria. How can they do that?

Scientists think that when tardigrades are under extreme conditions, such as dryness, their DNA breaks into pieces. When the cells rehydrate, the cell membranes become temporarily leaky, and DNA and other large molecules can pass right through. When the tardigrades repair their own damaged DNA, they stitch the foreign DNA into their own, creating a mixture of genes that come from different species.

Too bad humans can't absorb genes. Although humans have foreign DNA too, but not nearly as much as tardigrades. Most of it is from bacteria and viruses.

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