The Hawaiian bobtail squid is less than two inches long. It’s mud brown, feeds at night and is sometimes used as bait. In other words, the very definition of unassuming. But this tiny Sepiolidae could also change the way we think about, and treat, our bodies.
To understand why, you first have to understand circadian rhythms, the biological patterns that affect our sleep, digestion and other essential functions. Disrupting these rhythms can trigger an array of physical and psychological problems.
Prevailing wisdom suggests our circadian rhythms are controlled by exposure to light. But recent research suggests that might not be the whole picture—the bacteria in our gut could also play a key role.
Which brings us back to the bobtail squid. Biologists at the University of Wisconsin at Madison studied the squid and found that bacteria inside its body help wind its biological clock. If the same is true for mammals, and specifically humans, it could impact all sorts of things, including our frequent–some say overzealous–use of bacteria-killing antibiotics.
I spoke with UW-Madison grad student Elizabeth Heath-Heckman, who co-authored a paper published last month in the online journal mBiosphere, to find out how a tropical Hawaiian squid wound up being studied in the decidedly un-tropical Midwest—and what it means for all of us.
MAUITIME: Talk about the genesis of the study, and what led you to the bobtail squid?
ELIZABETH HEATH-HECKMAN: We’re looking at day-night cycles in the symbiosis, and how they’re influenced by bacteria. External light is on a very set cycle: you have 12 hours of day and 12 hours of night, especially in Hawaii where you’re very close to the equator.
But the bacteria that live inside the squid are bioluminescent, and produce light on a different cycle. Since a lot of circadian rhythms are influenced by light, we had the potential to look at whether the cycle of light that’s produced by the bacteria influences things in a different way than external light.
MT: Explain the importance of circadian rhythms; why do they matter so much?
HEATH-HECKMAN: They influence essentially every aspect of health. A lot of the functions of the gut are profoundly influenced by circadian rhythms, as is the immune system. There is a very large bacterial community there, but no one had really put the pieces together and asked, how do bacteria affect these circadian rhythms?
The reason this is so interesting from a health perspective is that there are very few chronic disorders that aren’t affected by aberrations in your circadian rhythms: heart disease, obesity, diabetes, some forms of cancer, just to name a few. We were drawn to the squid because it gave a simplified model.
MT: The conclusions you drew with the squid—how applicable are they to humans?
HEATH-HECKMAN: Since bacterial symbionts in the human gut don’t produce light, some people were skeptical about how well our research would translate to humans. But a paper just came out showing that the same thing happened in mice—if you take away their bacteria, then the genes that regulate circadian rhythms are not regulated properly anymore. So the bacteria in a mammalian gut, even if they don’t produce light, are still very important.
MT: What are the implications for the use of antibiotics? Could they be killing bacteria we need to stay healthy?
HEATH-HECKMAN: Possibly. If you take a single course of antibiotics, it doesn’t kill everything in your gut. What it does is changes what bacteria make up the community in your gut tract, though your body will slowly go back to its original state. The study we did involved taking away all the bacteria. So I think there’s a lot of work to do to find out whether changing the community as opposed to taking the community away can alter circadian rhythms. I do think there is a potentially profound issue there.
MT: Do you think this is an urgent line of inquiry, given the ubiquitous use of antibiotics?
HEATH-HECKMAN: I do. Pretty much all of the literature out there suggests that the bacteria in your gut are important, not just for digestion but for training your immune system, maybe even how your brain works and now for circadian rhythms. We should definitely keep investigating, and be as sparing as possible in how we use antibiotics. No one is saying we shouldn’t treat people who need it, but the idea of prophylactic or preventative antibiotics—we might want to ease up on that.
MT: What was it like working with a tropical squid in Wisconsin?
HEATH-HECKMAN: Obviously we could create the conditions for light and temperature that the squid needs. But I’ve been out to Hawaii to collect several times and do experiments, and seen them out in the ocean. It’s really wonderful, from my perspective, to be able to work with an animal where you see the native population.
A lot of people who work with symbiosis don’t get that opportunity—they work on mice and they have inbred mouse lines. There’s a very real and important role for having those lines, but you don’t get to see them in the wild. It changes how you think about your research, and how you approach it. We’re really looking at natural populations.
MT: So what’s next?
HEATH-HECKMAN: Our lab is definitely going to keep pursuing this. We have a lot of questions, and a lot of tools to answer them. And hopefully we’ve either inspired other researchers, or maybe we were just in the right place at the right time, to start asking these same questions.