Bobtails + Bacteria = BFF

Bobtail Squids, a species of Cephalopods closely related to Cuttlefish, have a unique way of protecting themselves against predators at night. With the help of glowing bacteria, the squid camouflages itself against the starlit night sky.


Bobtail squids, a species of cephalopods closely related to cuttlefish, have a unique way of protecting themselves against predators at night.

With the help of glowing bacteria, the squid camouflages itself against the starlit night sky.

Our partner, 'Science Friday,' has the story.

I think you'd have to be nuts to not think a bobtail squid is cute.

Those big black eyes, I think they're just the cutest things ever, but Hawaiian bobtail squid are basically the couch potatoes of the cephalopod world.

They sit in the sand for much of their lives.

They do occasionally get up to hunt, but they're effectively, like, relaxing on vacation in Hawaii.

♪♪ My name is Sarah McAnulty, and I'm a squid biologist.

I study the symbiosis between Hawaiian bobtail squid and their beneficial bioluminescent bacterial partner.

A bobtail squid is a small squid that lives off the coast of Hawaii.

They're nocturnal, and they're about the size of a lime.

So these squid swim around at night, and it's basically like the squid has a constantly glowing lightbulb situated sort of in the center of the squid's body on the underside, and that lightbulb is all chock-full of bacteria called Vibrio fischeri.

If you're a cephalopod, you're super easy to eat.

You're basically like a swimming protein bar, so you have to be very good at camouflaging.

Typically if the squid wasn't glowing, it would look like a little squid-shaped shadow or silhouette.

With the help of the bacteria, they match the moonlight precisely coming down from above.

That partnership is called 'symbiosis.'

The bacteria gets a place to live, and if you're a squid, from the bacteria, you get light as camouflage.

Now, in terms of how the bacteria get into the light organ, this is a really cool process.

They go through this molecular gauntlet.

The squid is constantly beating cilia in the opposite direction of where the bacteria needs to swim, so these bacteria need to be awesome swimmers, and they also need to be able to put up with a lot of basically insults from the squid.

You've got nitric oxide.

You've got acid, but this Vibrio fischeri is able to eventually swim actively down pores and ducts into the depths of the light organ, and we call that deep area where the bacteria are trying to get to the crypt.

And once they're there, the immune cells also play a role in this specific symbiosis.

♪♪ My work is trying to understand how immune cells, which we call 'hemocytes,' are able to tell the difference between beneficial bacteria and others.

So I've developed a test and a method for watching the behavior of hemocytes.

The way I do this is, I take a squid from downstairs in the squid room, and I anesthetize it using ethanol.

It knocks them out completely, and I do a blood draw.

I only take out, like, a tiny drop of blood from these little squid, and then I'll do what I call squid PR, which is just, like, CPR on a squid.

I'll blow water over their gills using a pipette.

I'll tap them a little bit, and they burst back into life with color.

♪♪ So we take the blood out of the squid, and then we stain the immune cells with a dye, so we have bacteria in one color, and then we have a different type of bacteria in another color, and then we have the immune cells in far red.

We look at these different colors to tell who's who, and then I take time-lapse videos of these different cell types all interacting.

When the immune cell finds a bad bacteria in this context, it just engulfs it and eats it and kills it, but with Vibrio fischeri, it will bind, maybe carry it around for a little while, and then it just sort of, like, leaves it behind.

So, we think that there's some kind of education process that occurs between the bacteria and the squid at the beginning of the squid's life to sort of teach the immune cells that Vibrio fischeri is the beneficial bacteria.

The immune cells will migrate into the crypts where the bacteria live at night, and they will basically sacrifice themselves to feed the bacteria.

This is totally nuts and super cool because normally you would think of an immune cell as being just, like, a destroyer, not as something that would be feeding bacteria of all things, but this group found that this is what's going on.

The bacteria in the squid have been living together so long that they've both adapted to helping each other and being the perfect life partners.

It may seem bizarre, but it's really important because these squid are giving us a really unique opportunity to understand how animals and bacteria relate and how the colonization by bacteria affects your whole immune system, affects your whole genome and what far-reaching parts of the body are affected by having beneficial bacteria live with you.