Bacteria Makes Squid Sparkly and Sleepy

Bacteria sets up shop in squid to make it sparkle, and also might tell it when to go to sleep

Nick Hobgood

At this point, it seems clear that we’re all just slaves to microbes. Our microbiome, in many ways, makes us who we are, and microbes can even turn their victims into zombies. Here’s one recently discovered example—a particularly weird way in which bacteria alters the way a squid lives.

The bacteria Vibrio fischeri has a symbiotic relationship with the Hawaiian bobtail squid. The squid is nocturnal and relies on the bacteria bioluminesce. This relationship is mutually beneficial. The bacteria gets a place to live, food and help reproducing. The squid gets a nice light show that helps to camouflage it from predators.

But it turns out that the lights from V. fischeri do more than just mask the squid from hungry peers. Apparently these lights might have something to do with the squid’s circadian rhythm, helping to regulate when it gets up and when it sleeps. Holly Bik at Deep Sea News explains:

This is crazy but totally cool biology – its akin to us humans being required to drink probiotic yogurt in order to sleep. In this hypothetical scenario, our own body wouldn’t know when it should sleep on its own, since sleep would only be cued after our body detected the correct signals from bacterial proteins.

It gets even weirder. According to Discovery News, the squid and the bacteria have a strange daily cycle. Biologists think that every morning, the squid spits out 95 percent of the bacteria, and some of its own cells to feed them. The expelled bacteria are taken up by younger squid, while the adult settles back into the sand to sleep and grow a new batch of V. fischeri, which only glows when it reaches a certain concentration.

While we humans are dependent on our microbes, the squid can live without their bacterial friends for light. But who doesn’t prefer to be sparkly when they go out for the night?

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