Some Scientists Believe That Space Travel Alters The Human Microbiome, Which Is Linked To Many Diseases.
From black holes to cosmic heat death, space is dangerous for humans. But as humanity contemplates long-term space travel, more minor potential risks may deserve more attention. One of them is terrestrial microbes.
On Earth, researchers are beginning to understand how the various bacteria and other microorganisms that live inside and outside the human body (the human microbiome) affect our physical and mental health.
Of course, space is an entirely different environment than Earth, with high radiation levels and microgravity. Although the science is inconclusive, these vast differences may cause unexpected changes in the astronauts’ microbiomes. This, in turn, can lead to various health problems that may be more pronounced during extended space travel, such as travel to other planets.
David Pearce, a life sciences researcher at Northumbria University and author of a paper published in 2022 looking at how a trip to Mars might affect the gut microbiome, says the consequences of microbiome disruption are poorly understood, even on Earth.
Direct research on the impact of space travel on the human microbiome is limited, as only about 600 people have gone into space so far. Those who go on space trips usually don’t stay long, as the average trip to the ISS is about six months.
However, some researchers are still not convinced that there is enough evidence to show that the human microbiome undergoes a significant change in space. However, many researchers, including Pierce, are trying to find out if astronauts develop a condition called dysbiosis, in which their microbiome undergoes unfavorable changes.
Researchers try to investigate the possible effects of space on the microbiome in two places:
In environments on Earth with conditions similar to play and freedom itself.
In an example of the first, Norberto González Yorba, a researcher in the Astronaut Microbiome Research Group in the Genomic Medicine and Infectious Diseases Group at the J. Craig Venter Institute, is studying the microbiome of researchers working at the Concordia and Newmayr stations in Antarctica. González Yorba says that these places are somewhat similar to where astronauts are, especially in terms of darkness, confinement, and limited human contact.
González Yavarbe and his colleagues plan to analyze samples from researchers at these stations to see how the microbial composition of their digestive tracts changes and how their immune systems react to the space-like conditions at the research station.
According to González Yorba, preliminary results indicate changes in gut microbes, and the research team is reviewing immunological data. He predicts that the results of their studies will be published by the end of this year.
Studies conducted in space are few. For example, a 2019 study compared the microbiomes of astronaut Scott Kelly and his twin brother Mark. Scott had been on the ISS for about a year since 2015. The study claimed that Scott’s microbiome had changed in space. For him, this change included a decrease in Bacteroidetes, whose dysregulation has been associated with neurological and immune system problems and metabolic problems, and an increase in Firmicutes. These bacteria can help break down certain starches and fibers.
In 2019, another study from the J. Craig Venter Institute looked at nine astronauts who had spent between six and 12 months on the International Space Station. The astronauts collected samples from different parts of their skin, nose, and tongue. They also collected samples of their feces, blood, and saliva, along with representatives from various levels of the station and its water tank.
Once the samples were in the hands of the scientists, they extracted and sequenced the samples’ DNA to see how the astronauts’ microbiomes changed over time.
This study showed that the number of different skin microbes, including types of gammaproteobacteria, had decreased, which, according to the authors’ hypothesis, could contribute to the common phenomenon of rashes and severe skin sensitivity among astronauts in space. These findings also showed that the microbiome of the astronauts’ digestive tract had changed and the population of two types of bacteria (Acremansia and Ruminococcus), which seem to play an essential role in maintaining the integrity of the digestive tract mucosa as well as in the breakdown of carbohydrates, had decreased fivefold.
Altering the gut microbiome can affect food metabolism, bone health, and even cognition, said González Yorba, who was not involved in the 2019 study. Longer journeys in space (such as an 18-month trip to Mars and back) are likely to exacerbate these problems. “Changes in the microbiome will have implications for overall brain health and cognitive health,” he said.
Still, not everyone is convinced that the human microbiome changes in space. According to Jack Gilbert, professor of pediatrics at UC San Diego and chair of the biology department at the Scripps Institution of Oceanography, the number of participants in the existing studies was too small to draw any conclusions. “With so few people in space, it’s difficult to do studies that have acceptable statistical precision,” he said.
Gilbert is also skeptical of the Kelly twin study: “We have many twin studies that we’ve compared over time on Earth, and they’ve all shown significant deviation.”
What could be of more significant concern to human health in space, Gilbert said, are microbes that can escape the body and mutate into more dangerous versions. A 2019 study by Gilbert and colleagues suggests this may be the case.
In March 2016, astronauts on the International Space Station collected samples from the station’s dining table.
Six days later, the samples were brought back to Earth. Gilbert and his team isolated the microbes in the models and selected two strains of the fungus Fusarium oxysporum, and sequenced their genes. The researchers then compared the isolated mushroom samples with 62 other songs. They found that the strains related to the space station samples differed from the genetics of their terrestrial counterparts.
The team also exposed small worms called nematodes to both samples. They found that some microbes from the International Space Station killed more worms. Gilbert said fungi might become more pathogenic in response to the harsh conditions of space, though his team is working on a new study to help clarify the connection.
Microbes prefer warm and moist environments like the environment inside the human body. Thus, microbes that escape from that habitat to cold, dry surfaces are also exposed to radiation and zero gravity and can acquire new survival skills over generations. “Some of those survival strategies are related to things like antibiotic resistance or increased virulence in humans,” Gilbert added.
Gilbert noted that astronauts chosen to go into space are often very healthy, so there is little chance of them getting sick from these rogue microbes. However, if a person on a long trip to Mars has a weakened immune system due to food poisoning or fatigue, they could be infected by these hardy microbes.
According to all the researchers who talked to Andark, there is very little research on the human microbiome in space, and many unknowns exist.
For example, Nicole Buckley, head of the European Space Agency’s SciSpacE program, noted that it’s difficult to say whether microbial disturbances cause problems like insomnia in space or whether microbes play a role in causing or responding to disease.
It’s also unclear how researchers can stabilize a person’s microbiome in space, so it doesn’t become disrupted and cause disease, Pierce said. For example, a fecal transplant, which contains loads of beneficial bacteria from the feces of a healthy donor to a sick person, can help restore immune functions in people with certain diseases. But because microbiomes are so complex, it’s not like prescribing a drug that has a specific outcome. You are taking an organism that may stabilize and have the desired result, or it may not achieve the expected result.
Although some researchers have noted that relatively simple changes could improve the health of astronauts, eating fresh fruits and vegetables and high-fiber foods can increase the microbes in the digestive tract that produce short-chain fatty acids that help support the immune system, Gonzalez-Yorba said. Buckley noted that prebiotic and probiotic foods could also be helpful.
According to Grace Douglas of NASA’s Advanced Food Technology Project, astronauts in space have access to freeze-dried foods that contain natural levels of food-associated microorganisms but are processed to avoid containing pathogens.
Astronauts also receive small amounts of fresh fruits and vegetables through resupply missions.
However, according to Buckley, a healthy microbiome requires minimally processed foods, more fruits and vegetables, and high-fiber foods.
The European Space Agency is conducting a study in which compounds found in human milk called oligosaccharides (a group of carbohydrates) will be added to the diet of researchers who stay at the Concordia research station in Antarctica for more than a year. These compounds are believed to be important in creating a healthy microbiome in infants. The study will test the effect of oligosaccharides on the researchers’ microbiome, immune system, and mood.
There are still other areas that need to be investigated and could increase scientists’ understanding of the effect of space on the human microbiome. For example, we need to learn more about individual astronauts and their microbial balance and what makes their microbiome stable or unstable, Pierce said.
Pearce added that astronauts might encounter familiar opportunistic pathogens (germs that are usually harmless but can become dangerous when a person’s immune system is weakened, such as methicillin-resistant Staphylococcus aureus (MRSA), which is found in two percent of people). But he said there might also be unknowns in the field: microbes that humans carry into space that have an unknown potential to become pathogens.
It’s currently impossible to say how the human microbiome would change during a long trip to Mars compared to a relatively short stay on the ISS, Pearce said. But given the timeline for a spaceflight to the Red Planet (which NASA plans for the late 2030s or early 2040s), scientists have plenty of time better to understand the microbiome’s role in astronaut health. Until then, researchers should continue their studies using all available tools.