Mold – organisms that are the most closely related to humans since they are not bacteria (even if this sounds strange) – is incredibly “robust”, to the point that several (undesired) species, found on the inside and outside walls of spacecraft, survive X-ray exposure at 200 times the dose that would kill a human. This was discovered by microbiologists at the German Aerospace Center in Cologne, who simulated the conditions of the International Space Station (ISS), by exposing the outside walls to high concentrations of radiation. The results of this study were presented at the “2019 Astrobiology Science Conference”, organized by the American Geophysical Union in Bellevue, USA.

The researchers focused their attention on the spores of two of the most common species of mold, namely Aspergillus and Pennicillium, always present in the ISS despite the constant daily cleaning carried out by the astronauts (the spores are reproductive cells, capable of remaining “silent” even for long periods of time and of creating new mold – which is a type of fungus). These species of mold are not usually harmful for humans, but, if inhaled in large quantities, can cause allergies, respiratory problems and various kinds of illnesses in people with weakened immune systems.

The German researchers applied X-rays up to 1000 gray to the spores (gray is the unit that measures absorbed dose of ionizing radiation; 5 gray is enough to kill a person). In addition, the spores were exposed to ionized radiation at 500 gray, using heavy ions (the threshold for radiation sickness in humans is 0.5 gray). Finally, they exposed the spores to ultraviolet rays similar to those found in space (and not on Earth) up to 3000 joules per meter squared (an “impossible” quantity for humans), and showed that the spores, despite everything, survived. Therefore, the extremely high “amount” of radiation did not appear to be capable of causing serious damage to the genetic material, as would be the case, on the other hand, in almost all other organisms, if exposed to this treatment.

Given that a mission to Mars takes around 180 days (during which it has been calculated that the crew will be exposed to 0.7 Gray) and that during this long voyage the outside walls of the spacecraft will be exposed to a bombardment of radiation certainly lower that the amount tested at the German Aerospace Center, it can be said that the spores will, probably, arrive intact on the Red Planet and that this could have a negative effect on the new environment they enter. In this regard the German researchers have suggested the creation of “protection” protocols designed to minimize the risk by visiting spacecraft of contaminating other planets in our solar system

Tests will now continue to check the ability of the spores to withstand microgravity, vacuums, the cold (other specific conditions characteristic of spacecraft) and combinations of these parameters, which during voyages to space vary dramatically, compared to Earth.

The extreme “resistance” of mold, however, is not, in itself, all bad: mold and yeast, in fact, are used today to produce vitamins, drugs and other kinds of molecules. In space, also thanks to their outstanding ability to survive, they could become mini biological “factories” for producing valuable molecules for astronauts and those that go on long space voyages.

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