Mold can grow in a vacuum

Space has a mold problem

Regular cleaning is also the order of the day in space stations, otherwise the notorious wall mold will spread there too. The problem with these stubborn fungi could go beyond this aspect in space travel, as tests are now showing: their spores could also survive on the outer shell of spacecraft, because they apparently even withstand the extreme radiation in space. In future missions to distant celestial bodies, mold could therefore represent a considerable risk of contamination for the distant worlds.

Ugly streaks and stains - wall mold! These musty sub-tenants are spreading in many living spaces. It is astonishing how little these mushrooms need to survive: a fine precipitation of moisture and dust particles as a food source are sufficient for them to grow. Interestingly, wall mold is also a problem in mankind's highest dwelling: On the International Space Station ISS, Penicillium and Aspergillus species are found on the surfaces.

How tough are the survivors?

The astronauts on the ISS therefore intensively clean the walls every week so that the mold does not grow into a nuisance and a health risk. Because inhaling the fine spores in large quantities can be problematic for humans. However, the cleaning measures cannot completely destroy the unpopular roommates in space. It is known that molds are not only amazing survivors, but also have enormous resistance to chemical and physical stress. Its tiny spores, in particular, can withstand extreme temperatures, ultraviolet light, chemicals, and dry conditions.

But you might think that even they cannot withstand the enormous radiation exposure in space without protection. To what extent this is the case, Marta Cortesão from the German Aerospace Center (DLR) has now explored. In the laboratory, she exposed spores of Penicillium and Aspergillus to simulated space radiation: She treated the tiny creatures with different doses of X-rays, heavy ions and high-frequency ultraviolet light that does not reach the surface of the earth, but only radiates in space.

What radiation can cause in living things is well known: it can kill cells by damaging their DNA and other important cellular structures. Space stations like the ISS are largely protected from the strong radiation of interplanetary space by the earth's magnetic field. But spacecraft going to the moon or Mars would be exposed to it.

Survival on the outer shell seems possible

As Cortesão now reported at the Astrobiology Science Conference in Bellevue, the spores survived exposure to ultraviolet light of up to 3,000 joules per square meter and X-rays up to a dose of 1,000 gray and heavy ions up to 500 gray. Gray is a measure of the absorbed dose of ionizing radiation or radiant energy per kilogram of tissue. Five gray are already enough to kill a person and half a gray is considered the threshold for the development of radiation sickness. This is an important issue when planning manned space flights to Mars. Protective devices must limit the burdens for travelers.

For the fungi, however, according to the results, radiation is apparently rather “not an issue”. “It has been shown that the spores can withstand far more radiation than expected,” says Cortesao. "Even on a long-term mission, we must expect to have them with us, as they could survive space travel even on the outer shell," says the microbiologist. According to her, this could have a meaning above all for the protection protocols, which are intended to prevent spacecraft from contaminating other planets or moons in our solar system with microorganisms from Earth. In this context, the importance of fungal spores is once again coming to the fore.

However, important questions still remain open: It is unclear, for example, to what extent the fungal spores can withstand the combination of radiation, vacuum, cold and weightlessness in space. Further investigations should therefore now sound out the capabilities of these amazing organisms in even more detail: Corresponding tests are to begin at the end of 2019.

Source: American Geophysical Union

June 28, 2019

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