The Hawaiian bobtail squid (Euprymna scolopes) has an internal alarm clock thatâ€™s run by a species of glowing bacteria known asÂ Vibrio fischeri. This bacterium and the squid are symbiotic, which means theÂ two species live together for mutual benefit.
Now aÂ recent study published in the journalÂ mBio shows thatÂ V. fischeri are required for the squidâ€™s daily circadian rhythm.
â€œThereâ€™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,â€ said study leader Elizabeth Heath-Heckman, a Ph.D. candidate in the lab of Margaret McFall-Ngai at the University of Wisconsin.
An organismâ€™s sleep-wake cycle is perhaps the most dramatic example of a circadian rhythm. But these rhythms alsoÂ regulate 98 to 99 percent of our bodyâ€™s genes, and have strong effects on everything from eating and digestion to how the immune system works.
â€œAn 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,â€ said Heath-Heckman,Â who has been studying these squid and bacteria for over two decades.