Drew Hendricks

Introduction: Hundreds of astronauts have traveled to space over the last 50 years, and many more will travel undergo long-term space travel soon^1–4. Space flight impacts many aspects of an individual’s health, most notably due to the effects of microgravity, radiation, and isolation^1–4. Importantly, these effects largely impact our most understudied organ: the microbiome. There have been observed changes in microorganisms in microgravity that impact human health such as the S. aureus showing an increased thickness of the cell wall peptidoglycan layer and other markers for decreased susceptibility to vancomycin⁵. Understanding how microorganisms and the microbiome react to the space environment will be crucial in how we diagnose and treat disease in space. Health risks associated with changes in the microbiome are not well understood, but studies have linked changes to neurological and physiological conditions². Methods: The two primary methods utilized to study the effects of microgravity on the microbiome include simulated microgravity in chronic mouse models and assessment of samples collected from astronauts while in space. The hind limb unloading model is a model of microgravity where a mouse is suspended from its hindlegs. Biological samples taken from astronauts included saliva, urine and stool samples before, during and after spaceflight. Results: Saliva samples taken from astronauts showed there was a marked change in the microbial profile before, during and after spaceflight⁴ . Physiological metabolism itself was seen to be significantly influenced by microgravity⁶. In the hind limb unloading model, researchers identified changes in certain metabolism that were significantly correlated with the change in microbial profile due to microgravity⁷ . As well as metabolic changes due to microgravity, changes in immune function were also significantly correlated with the alteration of microbial and metabolic profile⁷ . These changes in microbial physiology may increase the danger of infection and sepsis in space. The expression of certain antibiotic resistance genes was found to have significantly increased during spaceflight, and the expression of virulence factors was also significantly altered in spaceflight ⁸. Conclusion: Changes in the microbiome brought on directly or indirectly by the space environment undoubtedly may lead to changes in how we care for healthy and sick astronauts in space. If we can better understand the implications of microorganism modification in space environments, we will be able to better diagnose and treat ailments in space as well as gain a broader understanding of how biological processes adapt to extreme changes in environment.

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