Jan 23 2024

Microbes Aboard the ISS

As I have written many times, including in yesterday’s post, people occupying space is hard. The environment of space, or really anywhere not on Earth, is harsh and unforgiving. One of the issues, for example, rarely addressed in science fiction or even discussions of space travel, is radiation. We don’t really have a solution to deal with radiation exposure outside the protective atmosphere and magnetic field of Earth.

There are other challenges, however, that do not involve space itself but just the fact that people living off Earth will have to be in an enclosed environment. Whether this is a space station or habitat on the Moon or Mars, people will be living in a relatively small finite physical space. These spaces will be enclosed environments – no opening a window to let some fresh air in. Our best experience so far with this type of environment is the International Space Station (ISS). By all accounts, the ISS smells terrible. It is a combination of antiseptic, body odor, sweat, and basically 22 years of funk.

Perhaps even worse, the ISS is colonized with numerous pathogenic bacteria and different types of fungus. The bacteria is mainly human-associated bacteria, the kinds of critters that live on and in humans. According to NASA:

The researchers found that microbes on the ISS were mostly human-associated. The most prominent bacteria were Staphylococcus (26% of total isolates), Pantoea (23%) and Bacillus (11%). They included organisms that are considered opportunistic pathogens on Earth, such as Staphylococcus aureus (10% of total isolates identified), which is commonly found on the skin and in the nasal passage, and Enterobacter, which is associated with the human gastrointestinal tract.

This is similar to what one might find in a gym or crowded office space, but worse. This is something I often considered – when establishing a new environment off Earth, what will the microbiota look like? On the one hand, establishing a new base is an opportunity to avoid many infectious organisms. Having strict quarantine procedures can create a settlement without flu viruses, COVID, HIV or many of the germs that plague humans. I can imagine strict medical examinations and isolation prior to gaining access to such a community. But can such efforts to make an infection-free settlement succeed?

What is unavoidable is human-associated organisms. We are colonized with bacteria, most of which are benign, but some of which are opportunistic pathogens. We live with them, but they will infect us if they are given the chance. There are also viruses that many of us harbor in a dormant state, but can become activated, such as chicken pox. It would be near impossible to find people free of any such organisms. Also Рin such an environment, would the population become vulnerable to infection because their immune systems will become weak in the absence of a regular workout? (The answer is almost certainly yes.) And would this mean that they are a setup for potentially catastrophic disease outbreaks when an opportunistic bug strikes?

In the end it is probably impossible to make an infection-free society. The best we can do is keep out the worst bugs, like HIV, but we will likely never be free of the common cold and living with bacteria.

There is also another issue – food contamination. There has been a research program aboard the ISS to grow food on board, like lettuce, as a supplement of fresh produce. However, long term NASA would like to develop an infrastructure of self-sustaining food production. If we are going to settle Mars, for example, it would be best to be able to produce all necessary food on Mars. But our food crops are not adapted to the microgravity of the ISS, or the low gravity of the Moon or Mars. A recent study shows that this might produce unforeseen challenges.

First, prior research has shown that the lettuce grown aboard the ISS is colonized with lots of different bacteria, including some groups capable of being pathogens. There have not been any cases of foodborne illness aboard the ISS, which is great, so the amounts and specific bacteria so far have not caused disease (also thoroughly washing the lettuce is probably a good idea). But it shows there is the potential for bacterial contamination.

What the new study looks at is the behavior of the stomata of the lettuce leaves under simulated microgravity (they slowly rotate the plants so they can never orient to gravity). The stomata of plants are little openings through which they breath. They can open and close these stomata under different conditions, and will generally close them when stressed by bacteria to prevent the bugs from entering and causing infection. However, under simulated microgravity the lettuce leaves opened rather than closed their stomata in response to a bacterial stress. This is not good and would make them vulnerable to infection. Further, there are friendly bacteria that cause the stomata to close, helping them to defend against harmful bacteria. But in microgravity these friendly bacteria failed to cause stomata closure.

This is concerning, but again we don’t know how practically relevant this is. We have too little experience aboard the ISS with locally grown plants. It suggests, however, that we can choose, or perhaps cultivate or engineer, plants that are better adapted to microgravity. We can test to see which cultivars will retain their defensive stomata closure even in simulated microgravity. Once we do that we may be able to determine which gene variants convey that adaptation. This is the direction the researchers hope to go next.

So yeah, while space is harsh and the challenges immense, people are clever and we can likely find solutions to whatever space throws at us. Likely we will need to develop crops that are adapted to microgravity, lunar gravity, and Martian gravity. We may need to develop plants that can grow in treated Martian soil, or lunar regolith. Or perhaps off Earth we need to go primarily hydroponic.

I also wonder how solvable the funk problem is. It seems likely that a sufficiently robust air purifier could make a huge impact. Environmental systems will not only need to scrub CO2, add oxygen, and manage humidity and temperature in the air aboard a station, ship, or habitat. It will also have to have a serious defunking ability.


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