May the Fourth Be With You… and With Your Microbiome

May 4th has long been an unofficial Star Wars holiday, thanks to a somewhat silly pun. (“May the fourth be with you!”) This year, fans have even more reason to celebrate: the newest movie in the franchise, Solo, comes out in just a few weeks.

Solo traces the origin story of space smuggler Han Solo, whose love of blasters and Princess Leia was made famous by the original trilogy. Other theater-goers may be transfixed by the film’s dramatic space battles and depictions of exotic alien species. For us, however, watching the Millennium Falcon hyperjump across the big screen will bring only one question to mind: how would all of this interplanetary space travel affect human gut flora? 

Connecting Star Wars to the human microbiome isn’t such a stretch. At least one peer-reviewed scientific article has compared our gut flora to “midi-chlorians”—microorganisms in the Star Wars universe that dwell inside human cells and allow Jedis to sense and use the Force.

In this universe, of course, microorganisms can’t help us wield lightsabers or levitate rocks in a Dagobah swamp. They do, however, help us digest our food, maintain our immune systems, and play a role in regulating mood—functions which are quite powerful in themselves. If space travel disrupts the delicate balance of bacteria in our guts, it could have major implications for humans’ ability to engage in Star Wars-like interplanetary journeys in the future.


What we can learn from astronauts’ unbalanced gut flora

That is partly why over the course of its 60-year history, NASA has commissioned multiple studies of what goes on in astronauts’ guts while they’re free of earth’s gravity. Researchers have looked at stool samples from astronauts before, during, and after they spent time on the space station Skylab and found that their gut microbiome lost diversity while in space. According to an article by researchers from the J. Craig Venter Institute, the likely culprits were the sterile conditions astronauts endured on the station: they couldn’t eat fresh food and breathed heavily filtered air.

More recently, researchers from Northwestern University compared the microbiomes of astronaut Scott Kelly and his identical twin, Mark, after Scott had spent a year on the International Space Station (ISS). They found that the balance between two major groups of gut bacteria—Firmicutes and Bacteroidetes—shifted significantly while Scott was in space but returned to normal once he got back to Earth. These researchers are still trying to figure out why the shift happened and what impact it might have had on Scott’s health.


Bacteria behave strangely in space

Shifts in diet and environment partly explain the fluctuations in astronauts’ microbiomes; however, the picture could be a bit more complicated than that. Other studies have shown that bacteria grow and behave differently in a zero gravity environment.

For example, some pathogenic bacteria become more virulent and resistant to antibiotics in space. Research published in 2017 revealed that E. coli gets physically smaller in zero gravity, so there is less surface area for antibiotics to attack; its cell membranes also grew thicker and more difficult to penetrate. The microbes also grow differently, clustering in groups so only some are exposed to the outside. Changes like this might be why space-grown salmonella kills mice almost one and a half times faster than its earthbound brethren.

This is a big concern for NASA, since space travel tends to weaken astronauts’ immune systems. It’s also potentially a clue as to why some gut bacteria might grow unusually fast in zero-gravity.


Flying to Mars? Pack some probiotics

If we’re being fair, most of these research findings probably wouldn’t apply to Han Solo and crew. In the Star Wars universe, spaceships have artificial gravity, so it’s unlikely bacterial growth would go out of whack on board. The somewhat grimy Millennium Falcon could hardly be described as a “sterile environment” along the lines of Skylab, either. It actually seems likely that Han would have a more diverse microbiome than average, due to his exposure to bacteria from many different planets. (That’s probably how he can digest whatever suspect dishes they serve at the Mos Eisley cantina in A New Hope.)

That said, NASA’s research on the human microbiome does have important implications for today’s astronauts. Though NASA’s plans for a manned mission to Mars appear to be on hold, Elon Musk claims that SpaceX will send humans to the Red Planet within the next decade. Since the round trip will take two years or more, it will be important to keep the astronauts on that mission healthy for the duration—and that includes keeping their microbiomes in balance. Whether they ingest probiotic pills or grow their own fruits and vegetables on board their spaceship (as the J. Craig Venter Institute researchers suggest), the first humans on Mars will likely take extra steps to take care of their gut health.