Glowing Bacteria Control Squid Hosts

SquidBeing jolted awake every morning by an alarm clock is plenty annoying, but at least that alarm doesn’t actually live in your body.

The Hawaiian bobtail squid (Euprymna scolopes) has an internal alarm clock that’s run by a species of glowing bacteria known as Vibrio fischeri. This bacterium and the squid are symbiotic, which means the two species live together for mutual benefit.

Now a recent study published in the journal mBio shows that V. fischeri are required for the squid’s daily circadian rhythm.

“There’s been a lot of work looking at how circadian rhythm in the host can affect symbiosis, but not many people have looked whether symbionts could affect the circadian rhythm in the host,” said study leader Elizabeth Heath-Heckman, a Ph.D. candidate in the lab of Margaret McFall-Ngai at the University of Wisconsin.

An organism’s sleep-wake cycle is perhaps the most dramatic example of a circadian rhythm. But these rhythms also regulate 98 to 99 percent of our body’s genes, and have strong effects on everything from eating and digestion to how the immune system works.

“An organism has different stresses at different times of the day, and pretty much every group of organisms out there, from bacteria up through us, has evolved the capability of keeping time,” said Heath-Heckman, who has been studying these squid and bacteria for over two decades.


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