Northwestern Scientists Investigate Gut Microbiome for NASA Twins Study

Mark Kelly (left) provided a baseline for observation on Earth, and Scott Kelly (right) provided a comparable test case in space.

When, four years ago, NASA astronaut Scott Kelly launched into space to spend a year in orbit, Northwestern University scientists (along with nine other NASA-funded groups across the country) launched a fascinating experiment. Kelly was half of it; the other half was his identical twin, Mark — also an astronaut — who remained on Earth as a ground-based control.

All of the investigators involved with the experiment were studying how living in space affects the human body, including changes in gene expression, bone density, immune system responses and telomere dynamics. The Northwestern scientists, led by Fred Turek, PhD, professor in the Weinberg College of Arts and Sciences, and in Feinberg’s Ken and Ruth Davee Department of Neurology and in Psychiatry and Behavioral Sciences, focused on how outer space affects the microbiota “ecosystem” in the human gastrointestinal (GI) tract. All ten studies were published in one comprehensive paper in Science.

“This multi-system, integrated analysis over time is one thing that makes the Twins Study unique and powerful,” said Martha Vitaterna, PhD, the first author of the Northwestern study. “We can see which things change together in the human body.”

Turek and his team’s study found that extended spaceflight does affect the human gut microbiome. During his stay on the International Space Station (ISS), astronaut Scott Kelly experienced a shift in the ratio of two major  categories of bacteria in his gut microbiome.  The diversity of bacteria in his microbiome, however, did not change during spaceflight, which the Northwestern University-led  research team found encouraging.

“We cannot send humans to Mars without knowing how spaceflight affects the body.”

Fred Turek, PhD

The investigators collected two fecal samples from Scott Kelly before he left for space, four during the year in space and three after he returned to Earth.

“We did compare Scott with Mark, which was interesting,” said Turek. “But the real comparison was looking at Scott’s samples from before, during and after flight. That’s probably the most valuable information we have.”

More than 90 percent of the gut’s bacteria belong to one of two broad categories: Firmicutes or Bacteroidetes. Both categories contain a mix of both good and bad bacteria. The ratio between Firmicutes and Bacteroidetes in Scott Kelly’s microbiome experienced a pronounced shift during spaceflight — the number of Firmicutes increased while Bacteroidetes decreased. This shift was among the greater compositional change that the investigators noted in Scott Kelly’s microbiome, which returned to normal after he came back to Earth.

“There was some kind of wholesale shift in remodeling of the structure of this community of microorganisms,” Vitaterna said. “We cannot say whether it’s good or bad.”

What Caused the Shift?

A number of variables could have influenced Scott Kelly’s microbiome while in space, including microgravity, increased radiation, shifts in circadian rhythms, decreased sleep time, lack of air circulation, the stress of living in an enclosed space and an altered diet. Turek and Vitaterna were concerned that Scott Kelly’s diet in space, which comprised mostly freeze-dried, irradiated, pre-packaged foods, would decrease the diversity in his microbiome. Initially, diet does not appear to matter as much as the scientists worried.

This result mirrored mouse studies the Northwestern pair conducted in the past. Whereas Scott and Mark Kelly did not eat the same foods during the yearlong study, mice in previous studies ate the exact same diet. Still, the space mice experienced shifts in their gut microbiomes compared to the control mice on Earth.

Turek believes microgravity’s effect on bacteria is most likely responsible for the change. “That’s what we want to determine going forward,” he said.

The study’s finding could help physicians and scientists pinpoint and implement ways to protect astronauts’ and space tourists’ microbiomes during long bouts of space travel, such as during the much-anticipated mission to Mars. These countermeasures could include pre-, pro- and postbiotics.

“We cannot send humans to Mars without knowing how spaceflight affects the body, including the microbes traveling with humans to Mars,” said Turek. “And we need to know sooner rather than later. The plan is to send people to Mars in 2035, so we cannot wait until 2033 to gain this information.”