Jun 28 2019

Mold In Space

There are bacteria and mold aboard the International Space Station (ISS). This should come as no surprise, as these organisms follow humans everywhere we go. In fact it’s claimed that the ISS astronauts spend several hours per week cleaning mold off the ISS and wiping everything down. However, this first hand report by ISS astronaut Clayton C. Anderson says he did his cleaning duty every Saturday, but not as thoroughly as requested.

Still, as we spread into space, we need to carefully consider the microscopic ecosystem we will bring with us. A space ship or station is a self-contained environment, and as we plan trips back to the Moon and on to Mars, there will be longer and longer missions. Something as simple as a fungus may threaten those missions. A recent study of the resilience of mold spores highlights how challenging this may be.

The study looked at the effects of ionizing radiation on mold. They looked at the two most common species of mold aboard the ISS,  Aspergillus and Pennicillium. They found:

The spores survived exposure to X-rays up to 1000 gray, exposure to heavy ions at 500 gray and exposure to ultraviolet light up to 3000 joules per meter squared. Gray is a measure of absorbed dose of ionizing radiation, or joules of radiation energy per kilogram of tissue. Five gray is enough to kill a person. Half a gray is the threshold for radiation sickness.

Those are some hardy fungi. For context a one-way trip to Mars is expected to expose travelers to 0.7 gray. That will be a problem for the humans aboard, not so much the molds.

As an aside, the exposure to radiation is a major limiting factor for space travel. The ISS is still within the Earth’s magnetic field, and so is somewhat protected. But anything beyond low earth orbit will be slowly fried by radiation. We need to figure out how to shield our ships and colonies if we are going to have a prolonged presence outside of low earth orbit. This, by the way, is why lava tubes may be the best location for stations on the Moon or Mars.

But in any case, while we may struggle with the radiation, our microbial friends will not. This raises the specter of contaminating other worlds without microorganisms. Certainly whereever humans go, they will go also. But can mold spores survive on the outside of probes and other craft? That remains to be seen. They will then have to deal with not only the radiation but also the cold and vacuum. Further experiments are planned to test their resilience to these conditions.

I suspect the vacuum and cold will not be a problem for the spores. Prior experiments showed that tardigrades, small animals that can go into a dehydrated suspension, can survive the vacuum of space. When they were returned to Earth after 10 days they were rehydrated, and 68% survived and were able to lay viable eggs.  Interestingly, however, those exposed to the ultraviolet light from the sun, without the protection of the atmosphere, did not do well. Only a small percentage survived, and probably would not have survived a longer exposure. The mold spores therefore appear to be more resilient even than the famous tardigrades.

This creates the possibility of accidental contamination of other worlds that we explore. If humans colonize a world, then we absolutely will contaminate it. We have to assume that. But it could be a problem if our probes could contaminate a world, especially before we have determined if there is any native life. If we drill below the ice of Europa will we find life, or seed life?

But the study authors also point out that the hardiness of molds may also be an advantage. Mold are fungi, which are eurkaryotes (like animals). They can be engineered to produce useful compounds, such as drugs, enzymes, and nutrients. We already use molds to produce antibiotics and other compounds. They could be useful portable chemical factories that astronauts can take with them on long missions. It’s not necessarily a bad thing that microorganisms will follow us everywhere. We simply need to be prepared for this. We tend to think of bacteria, for example, as “germs” But most bacteria are benign, and some are helpful. Only a small percentage are harmful to humans. The same is true of yeasts, which are another kind of fungus. They are used for baking, brewing, and making cheese. They too have been hijacked for manufacturing drugs.

Also we are at the very beginning of researching the use of probiotics and other interventions to alter our gut bacteria. Engineering our own microbiota may have incredible health benefits. It is an exciting technology with a lot of potential, but again I caution we are at the very beginning of this story and it’s still hard to tell what applications will pan out.

The bottom line of all this is that microorganisms are powerful little factories. We should not think of them as only germs and pests. They are, rather, not only part of the natural world (we could not live without our bacteria), but are part of an important and growing technology. We will likely take this technology into space with us. But like all powerful technologies, we have to respect the risks and take reasonable steps to minimize them. Understanding these little critters is critical to that, and research aboard the ISS and elsewhere is helping us understand how hardy some of them can be.

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