Bdelloid Rotifers: Amazing.

This is a short piece about bdelloid rotifers, which are absolutely amazing little animals. For the more scientifically literate of you, I'll point you right here, which is a paper about what I'm explaining below. Somebody on reddit asked me to please "translate that page into idiot for me," which turned into a fairly long explanation of the basic concepts involved that hopefully explain why they're amazing. And so we begin.

Basically, rotifers are tiny animals that live in pretty much every watery environment on the planet. If you've ever accidentally swallowed some lake or river water, congratulations, you've eaten some. Bdelloids are a special group even beyond their ancient asexuality, because they can survive dessication - complete dryness - at any life stage.

Many organisms can do this at certain periods in their life, like some plant seeds can lie in a dry desert for months or years and suddenly start growing when water shows up. But remove all water from the environment of a grown plant, or any animal, and they die extremely quickly. All the water evaporates, their cell membranes fracture and break open, exposing the cell interiors to the environment. And DNA tends to crack and break apart, too.

Well, bdelloid rotifers routinely survive the complete absence of water for long periods of time. Years. Decades. You surprise them at any stage of their life cycle by drying them out, and they go dormant. You then let them sit there for basically as long as you want. Then you pour water back on them and BAM - little bastards spring back to life like nothing happened. It's incredible.

One of the things you need to survive this kind of damage is DNA repair mechanisms - something to take the fractured and broken DNA and stitch it all back together. Now, this is done in basically every living organisms, but bdelloid rotifers are just really, really good at it. An undergrad in my lab did some radiation testing on rotifers, which causes various types of DNA damage, and bdelloids can survive MASSIVELY higher radiation doses for much longer periods of time than...basically anything else. But these rotifers don't live in particularly radioactive environments, so it's odd that they seem well-adapted to survive lots of radiation. Luckily for them, the same kind of DNA repair you need to survive drying out is the same kind of repair mechanism you need to survive radiation. This DNA repair is actually really interesting for a lot of reasons, including human medical conditions like cancer and aging.

Well, they took a close look at bdelloid rotifers for various reasons, and sequenced the genome. Then they compared the genetic sequence - the literal order of GATCs in the DNA - to other creatures. And what they found was astonishing. They found plant genes. And bacterial genes. Now, it's important to note that all living organisms share some ancestral genes, like some involved in DNA replication. But the amazing part about genetics today is that we can tell the difference. Give me the sequence of a shared gene and, with some freely-available online databases, I can probably tell you whether it's most closely related to a plant, animal or bacteria. Even if it's a gene that does close to the same thing in every living organism on the planet.
So they didn't find a gene that had the same function in rotifers and other animals and plants. They found a gene whose nearest match was found in a modern plant. They found another gene whose nearest match was in e. coli bacteria. This...shouldn't happen. It basically makes no sense. But even beyond that, the e. coli gene was extra weird. It was clear that the rotifer was actually using the gene.

I'm not sure if you'll have an understanding of introns and exons but, without getting into it, think of bacteria genes like a text file. It just reads beginning to end. Higher-order creatures like plants and animals - rotifers - use "junk" sections inserted in the middle of the genes (for various reasons). Think of it like encryption - bacteria genes are not encrypted, but rotifer genes are. If you stick a rotifer gene in a bacteria, the bacteria will make garbage. If you stick a bacteria gene in a rotifer, though, it will work just fine.

But here's the crazy part - the e. coli bacteria gene in the rotifer? It was "encrypted." The rotifer had taken this bacteria gene and inserted an intron garbage section (that has to be removed to make a proper protein). But if you ignore the inserted section, the gene is an excellent match to a bacteria. Additionally, the rotifer had added some very specific sequences to the front end of the gene that helps the rotifer find and start producing protein from the gene.

So this is just batshit. What they think is happening is pretty cool, though. These bdelloids get dried out, and they crack open. Eventually, water rushes back over them and they start up their life cycle again. But when they are first exposed to water, they're actually cracked open. They think that, basically, DNA from other, dead creatures that's just floating around in the water flowed INSIDE these rotifers as they woke up. The rotifers begin stitching all the DNA that's broken apart. But for reasons I won't go into, the DNA repair mechanisms can't tell the difference between the rotifer's own DNA and the DNA that came from the environment. It just stitches the foreign DNA right in next to the regular DNA, and the rotifer starts life again, not even caring.

So at some point in the past, there were bdelloid rotifer ancestors that were dried out and had sections of DNA from plants or bacteria washed into them, which they took up and kept around. But not only that, they started actually using some of those genes from other creatures. It's as if you put a bunch of tiny animals and some algae into a blender, hit puree, and hybrids came out. Well, that's overstating it, but still.

THAT is why bdelloid rotifers are absolutely crazy. And, if you're a biology nerd like me, completely awesome.

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