We humans consider ourselves individuals and are proud to do so... but we're actually teeming with trillions of microbes, who do a lot for us in return for living in our bodies.
According to the American Society of Microbiology, bacteria outnumber human cells in the human body by 10 to 1, and they're responsible for a lot of what goes on. The collection of these microscopic organisms is known as the microbiome.
For example, the gut microbiome doesn't just help the human digestive system stay healthy in myriad ways, it can also influence food choices. The microbiome may play a role in diseases such as diabetes, rheumatoid arthritis and multiple sclerosis, and conditions such as autism, but it also protects us against other diseases and harmful bacteria, helps us digest food, and it may even be able to influence mood. Our microbes are deeply important, and we're still trying to understand how and why.
What we do know is that, when NASA sends astronauts to Mars, those trillions of microbes will be going too, so it's very important to gauge how a long-term stay in a space microgravity environment is going to affect them.
This research is occurring as part of the One-Year Mission aboard the International Space Station. Astronauts Scott Kelly of NASA and Mikhail Korniyenko of Russian space agency Roscosmos are currently spending a year in space as a feasibility study for the Mars mission, which will see astronauts spend at least a year in space on a return trip to Mars.
One of the biggest problems is lack of fresh food. We replenish our microbiome by consuming fresh fruits and vegetables, and probiotics such as yogurt. All of these are in short supply in space (which is partially the reason NASA is researching how plants grow on the ISS), and NASA is currently researching the impact of this lack on the microbiomes of Kelly and Korniyenko, who arrived on the ISS in March 2015 and will return to Earth in spring 2016.
To do so, they are taking periodic samples from each of the two men and the space station: blood, saliva, gastrointestinal samples, perspiration, body swabs, equipment swabs and potable water samples. These will help determine how not just diet, but also microgravity, environment and stress affect the microbial populations.
This could help the NASA medical team come up with measures to prevent microbe population loss, which could in turn lead to decreased metabolic function and infection by harmful microbes. Studying how microbiome changes affect a human host in space and why could also help figure out how these changes work on Earth, and how they can be mitigated.