Our Gut Microbes Have Circadian Rhythms, Too — And They Might Own Us

The community of microorganisms that lives on and inside you is known as the human microbiome, and it's all the rage these days. We used to do just about anything we could to kill the bacteria, archaea, viruses and fungi that call us home, but now many of us spend our days trying to encourage friends to try kombucha and kimchi for their tummy aches and spritzing ourselves with $50 bacteria spray. We even take probiotic supplements which we consume with prebiotic bacteria food, all in order to make sure the probiotics have some snacks to eat on their journey to our guts.

Yes, we've got a lot of bacteria in our bodies — researchers recently estimated that the average person has slightly more bacterial cells in their body than human cells. And because of our recent cultural obsession with the microbiome, in the past couple of decades, science has been pursuing the topic with fervor. What they're finding is that a healthy microbiome acts like a "virtual organ" essential to the performance of physiological functions like digestion, metabolism, and immune response. A debilitated microbiome can result in all kinds of medical troubles, from childhood asthma to colon cancer.

But a 2016 study suggests our microbiomes have their own circadian rhythms, just like we do, and that these daily rhythms have a lot to do with our health.

"This research highlights how interconnected the behavior is between prokaryotes and eukaryotes, between mammalian organisms and the microbes that live inside them," says lead co-author Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, in a press release. "These groups interact with and are affected by each other in a way that can't be separated."

Using cutting edge DNA sequencing technology, the research team found that the microbe communities living in the guts of mice have a pretty regular routine: different types of bacteria hang out in various areas of the intestines in the morning, moving around during the day, and ending up in a completely different place at night. So, each part of a mouse gut experiences differences in numbers and species of bacteria over a 24-hour period.

And that's not all: this bacterial migration affects host tissue that isn't even close to the gut. For instance, the research team found the daily rhythms of gut bacteria in mice really made a difference, depending on the time of day, to the liver's ability to detoxify blood and metabolize drugs. This aspect of the research is exciting because it could help biomedical researchers better understand how time of day and the microbiome may make a difference in the treatment of a disease.

Finally, the researchers found that the mouse's own circadian rhythms were essentially driven by those of its microbiome. There was no separating the two. However, when the microbiome was destroyed, some of the host mouse's genes that normally don't exhibit circadian rhythms took over for the rhythms of the microbiota.

So, what does this mean for us?

"What we learned from this study is that there's a very tight interconnectivity between the microbiome and the host. We should think of it now as one supraorganism that can't be separated," said lead co-author Eran Segal, a computational biologist at the Weizmann, in the press release. "We have to fully integrate our thinking with regard to any substance that we consume."

Which is probably his way of saying we should get lots of sleep — and no more midnight snacking.