Rodents went to space and returned with more gut bacteria, here’s what it means for astronauts

Understanding changes in the gut microbiome due to space travel could allow astronauts to avoid the loss of their bone mass in microgravity conditions.
Rupendra Brahambhatt
Representational image of rodents.
Representational image of rodents.


Both humans and animals who travel to space are expected to endure a decline in bone density as a result of the weak gravity conditions, but do you know that microgravity in space can also affect an astronaut’s gut bacteria? 

A team of researchers from the Forsyth Institute in Massachusetts recently sent 20 rodents to the International Space Station (ISS). Their latest study hints that during an astronaut’s (could be a human or a rodent or another mammal) journey to outer space, they might experience a rise in their gut bacteria diversity. 

“The gut microbiome is constantly monitoring and reacting, and that’s also the case when you're exposed to microgravity,” said Wenyuan Shi, one of the study authors and a microbiologist at Forsyth, in a press statement. 

According to the researchers, it is possible the changes in the gut could be behind the reduced bone density in astronauts while they are in space.

How did microgravity change the gut microbiome of rodents?

After spending 4.5 weeks in space, 10 of the 20 rodents that were flown to the ISS survived and came back to Earth. Shi claims that this is the first time in NASA’s history that rodents sent to space returned to Earth alive. 

The dead rodents were also brought to Earth after nine weeks. The researchers examined the gut microbiomes of these 20 rodents before they went to space after they arrived on Earth, and also at the end of their study. They compared this data to the gut microbiomes of 20 other rodents that were kept on Earth as a control group.

The researchers noticed that rodents who went to space had more gut bacteria than the control group rodents. Interestingly, for some reason, microgravity led to a significant increase in the number of bacteria belonging to Dorea and Lactobacillus species in the former group. Moreover, the gut microbiome population was highest in dead rodents who spent nine weeks (more time) in space. 

According to the study authors, it might be possible that the two abundant bacteria species in space rodents also contribute to an increase in the concentration of the metabolites which are also linked to bone mass loss in microgravity conditions.    

Explaining this assumption further, Joseph K. Bedree, the first author of the study, said, “When we mapped the genetic pathways for Lactobacillus and Dorea, they seemed to line up with the metabolites that were elevated during microgravity exposure.” 

He further added, “When someone’s in microgravity and experiencing bone loss, it would make sense that their body would try to compensate and that the biological systems within would be doing that as well, but we need to do more mechanistic studies to truly validate these hypotheses.”

What if gut bacteria really affect bone density in astronauts?

The bone mass of a mammal continues to change because of a natural process called bone remodeling. This process ensures optimal growth of bones and removal of damaged bone parts. Plus, it also allows our skeleton to adapt to different kinds of environments. 

According to the researchers, it is possible that some of the cells involved in bone remodeling also interact with metabolites produced by gut bacteria. Even some past studies also mention that gut bacteria can influence the bone remodeling process. 

Although the rodent study only highlights that the gut microbiome can undergo changes under microgravity, further research might confirm the connection between gut bacteria and bone density. 

In case this theory turns out to be valid in the future, it will be really groundbreaking because then scientists would be able to identify the bacteria in the gut responsible for reduced bone density in astronauts and keep them healthy even in extreme microgravity conditions. 

Moreover, the research might also give rise to new treatment methods for people on Earth who are living with diseases linked to bone loss. Hopefully, future studies will turn these exciting possibilities into a reality.

The study is published in the journal Cell Reports.

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