For over a century, people have dreamed of the day when humanity (as a species) would venture into space. In recent decades, that dream has moved much closer to realization, thanks to the rise of the commercial space industry (NewSpace), renewed interest in space exploration, and long-term plans to establish habitats in Low Earth Orbit (LEO), on the lunar surface, and Mars. Based on the progression, it is clear that going to space exploration will not be reserved for astronauts and government space agencies for much longer.
But before the “Great Migration” can begin, there are a lot of questions that need to be addressed. Namely, how will prolonged exposure to microgravity and space radiation affect human health? These include the well-studied aspects of muscle and bone density loss and how time in space can impact our organ function and cardiovascular and psychological health. In a recent study, an international team of scientists considered an often-overlooked aspect of human health: our microbiome. In short, how will time in space affect our gut bacteria, which is crucial to our well-being?
The team consisted of biomedical researchers from the Ionizing and Non-ionizing Radiation Protection Research Center (INIRPRC) at the Shiraz University of Medical Sciences (SUMS), the Lebanese International University, the International University of Beirut, the MVLS College at The University of Glasgow, the Center for Applied Mathematics and Bioinformatics (CAMB) at Gulf University in Kuwait, the Nuclear Physics Institute (NPI) of the Czech Academy of Sciences (CAS), and the Technische Universität Wien Atominstitut in Vienna. The paper that describes their findings recently appeared in Frontiers of Microbiology.
A microbiome is the collection of all microbes that live on and within our bodies, including bacteria, fungi, viruses, and their respective genes. These microbes are key to how our body interacts with the surrounding environment since they can affect how we respond to the presence of foreign bodies and substances. In particular, some microbes alter foreign bodies in ways that make them more harmful, while others act as a buffer that mitigates the effects of toxins. As they note in their study, the microbiota of astronauts will encounter elevated stress from microgravity and space radiation, including Galactic Cosmic Rays (GCR).
Cosmic rays are a high-energy form of radiation that consists primarily of protons and atomic nuclei stripped of their electrons that have been accelerated to close to the speed of light. When these rays are generated from elements heavier than hydrogen or helium, their high-energy nuclei components are known as HZE ions, which are particularly hazardous. When these impact our atmosphere or protective shielding aboard spacecraft or the International Space Station (ISS), they result in showers of secondary particles.
While Earth’s protective magnetosphere and atmosphere prevent most of these particles from reaching the surface, astronauts in space are exposed to them regularly. As the authors noted, previous research has shown how this exposure could potentially enhance astronaut resilience to radiation, a process known as radio-adaptation. However, they also noted that the extent to which astronauts adapted varied from one astronaut to the next, with some experiencing adverse biological effects before embarking on a deep space mission.
For this reason, they recommend conducting further research to determine the risks associated with the space environment, as it mostly consists of protons, which astronauts will be exposed to before encountering HZE particles. Third, NASA’s Multi-Mission Model suggests that an astronaut’s first mission can be an adapting dose. However, the team notes that current research suggests that a second spaceflight does not necessarily increase the chances of genetic abnormalities as much as expected. This could mean that the body may have a natural radio-adaptive defense mechanism.
In terms of recommendations, the team lauded the ISS as the ideal environment for testing the human microbiome response to space radiation and microgravity. They also address the shortage of research in this area and how the long-term effects of radiation on microbiomes and environmental bacteria are poorly understood:
“The International Space Station (ISS) is a unique and controlled system to study the interplay between the human microbiome and the microbiome of their habitats. The ISS is a hermetically sealed closed system, yet it harbors many microorganisms… In this context, NASA scientists did not consider that adaptation is not limited to astronauts and radiation exposure to bacteria inside an astronaut’s body or that bacteria inside the space station could induce resistance not only to high levels of DNA damage caused by HZEs but also to other bacterial activity-threatening factors such as antibiotics.”
Increased resistance to antibiotics could be life-threatening for astronauts, who face risks of injury and infection during long-duration missions. Furthermore, they emphasize how space travel and prolonged exposure to microgravity can weaken the immune system, reducing astronauts’ natural resistance to microbes – especially those with high levels of resistance to radiation, heat, UV, and desiccation, and can therefore survive in a space environment. As they summarize it:
“In a competition between astronauts and their microbiomes to adapt to the harsh space environment, microorganisms may emerge as the winners because they can evolve and adapt more quickly than humans by rapid acquisition of microbial genes. Microorganisms have a much shorter generation time, enabling them to produce many more offspring, each with unique genetic mutations that can help them survive in the space environment.”
For this reason, the research team stresses that additional research is needed to estimate the magnitude of adaptation in microorganisms before missions are mounted. This could be crucial for identifying potential risks and developing mitigation strategies, novel therapies, and interventions. They also recommend that astronauts undergo regular cytogenetic tests to measure their adaptive response and that only those who show a high adaptive response to low doses of radiation be selected for missions where they would be exposed to higher doses.
They also acknowledge that studying astronaut microbiomes in space presents several challenges. These include the difficulty of conducting experiments in the microgravity environment, which can affect the growth and behavior of microorganisms, making it challenging to obtain accurate and reliable data. There’s also the potential hazard of spreading pathogens in a closed environment with recycled air systems. However, this is research that needs to be conducted before crewed deep-space exploration can be realized, as it has the potential to identify potential pathogens and develop strategies to prevent their spread during missions.
Further Reading: Frontiers in Microbiology