Study homes in on cause of changes to gut microbiome of astronauts
A new analytical tool developed by researchers at Northwestern University has been used to reveal the effect of spaceflight on bacteria in the gut microbiome. The research suggests distinct microbiome changes caused by spaceflight are most likely caused by microgravity, and not radiation, diet or other factors previously hypothesized.
“If we are going to send humans to Mars or on long missions to the Moon, it is essential to understand the effects of long-term exposure of the space environment on us – and on the trillions of bacteria traveling with us,” explains Fred Turek, co-author on the new study.
Prior research has indicated spaceflight causes significant changes to the diversity of bacteria in the gut microbiome. This has been verified in mice delivered to the International Space Station (ISS), and in astronaut Scott Kelly who spent nearly a year in space.
Exactly what was causing these microbiome changes has not been entirely clear. In the case of astronaut Scott Kelly, whose microbiome could be directly compared to that of his Earth-bound identical twin brother, it has been hypothesized these changes were simply due to the specific dietary conditions of astronauts.
To try and get a clearer understanding of what was underpinning these microbiome changes, the Northwestern researchers developed a new method called STARMAPS (Similarity Test for Accordant and Reproducible Microbiome Abundance Patterns).
“There wasn’t a statistical approach for doing this work,” says Martha Vitaterna, lead researchers on the new study. “The tools didn’t exist, so we invented them. It’s a classic case of how necessity is the mother of invention.”
The new study crunched a load of data from several NASA rodent studies following groups of mice sent to the ISS, alongside matched control groups kept under similar conditions on Earth. The control mice kept on Earth were carefully housed in conditions identical to their space-bound counterparts, with matching diets, habitats, temperature and humidity levels.
The researchers are clear to note in the study that the primary differences between the groups of animals were, “the acceleration and vibration during launch as well as microgravity and cosmic radiation during spaceflight."
The effects of the launch on the animals cannot be excluded, say the researchers, however, it is estimated that this impact could not account for all the microbiome differences seen between the two animal cohorts. Radiation is often considered to be a factor at play here, but the new study could effectively rule that out by comparing spaceflight data to specific studies done on mice exposed to similar space-type radiation on Earth.
“Radiation definitely has an effect on the gut microbiome,” says Vitaterna. “But those effects do not look like what we saw in spaceflight.”
The current hypothesis to explain these differences in gut microbiome composition is that they are fundamentally caused by specific environmental factors found in space. Microgravity in particular is cited as the most likely primary factor at play.
Comparing the animal data to the microbiome samples taken from Scott Kelly while on the ISS, the researchers found distinct similarities between the groups. This suggests these microbial changes are indeed caused by spaceflight.
“Some of the high-level changes are similar,” says Peng Jiang, first author on the new study. “We saw the ratios of the same major types of bacteria change in the same direction and a slight increase in overall diversity. That is consistent.”
So how does microgravity directly alter a person’s microbiome? The study speculates a number of potential mechanisms could be at play, from lowered fluid shear dynamics to altered digesta movement, but Vitaterna does note these gut bacteria changes may be underpinned by stress responses in an organism.
Further work will inevitably be needed to better understand the effects spaceflight has on the microbiome, but the results may not only help our future astronauts stay healthy on long spaceflights – any method developed to help mitigate the stress of space environments could help us here on Earth, too.
“Understanding the factors that can reduce this kind of microbiome change would be useful information to have – for offsetting the effects of stress on Earth,” says Vitaterna. “Understanding what genetic factors contribute to differences in bacterial strains will be useful for developing countermeasures that can protect your microbiome during stressful periods.”
The new study has been published in the journal Microbiome.
Source: Northwestern Now