| dc.description.abstracteng | The International Space Station (ISS) is an indoor-closed environment in Low Earth Orbit (LEO). Outside of
the ISS, radiation is the most challenging factor outside. In turn, inside the ISS, spaceflight microgravity is
the one factor that cannot be evaded. Aspergillus niger and Penicillium rubens are two common isolates
of the ISS microbiota. As filamentous fungi, they form highly resistant airborne spores that can easily
spread and colonize the spacecraft habitat. Fungi surface-associated growth (or biofilm formation), can
biodegrade surfaces and clog life-support systems, and their spores can potentially infect the humans on
board. In contrast, on Earth filamentous fungi play an important role in biotechnology, producing a widerange of compounds of interest, from food to antibiotics. Because of this, envisioned long-term spaceflight
missions going far beyond low Earth orbit, to the Moon or Mars, will require an intensification of the fungal
research, not only in relation to astronaut health and spacecraft safety, but also establishing opportunities
for fungal-based biotechnology in space. Thus, this thesis aims to answer three main questions: i) can A.
niger spores resist space radiation, and if yes, could they endure interplanetary space travel? ii) if brought
to the surface of Mars, could A. niger spores survive the martian environment? and iii) how does simulated
microgravity affect A. niger colony growth and biofilm formation? In total, four strains of A. niger were
analyzed in this thesis: the industrial and highly pigmented wild-type strain (N402), a strain defective in
pigmentation (ΔfwnA), a strain defective in DNA repair (ΔkusA), and a strain defective in polar growth
(ΔracA). To assess the level of resistance and survival limits of fungal spores in a long-term interplanetary
mission scenario, A. niger spores were exposed to high radiation doses of X-rays and cosmic radiation
(helium- and iron-ions) and of UV-C radiation. Results show that wild-type spores of A. niger were able to
withstand high doses of the all tested types of space radiation. This suggests that A. niger spores might
endure space travel, when considering the radiation factor alone. To evaluate the survival of A. niger to
Mars surface conditions, dried spores were launched in a stratospheric balloon mission called MARSBOx.
Throughout the mission, A. niger spores were exposed to desiccation, simulated martian atmosphere and
pressure, as well as to full UV-VIS radiation. Results revealed that the highly pigmented wild-type spores
would survive in a Mars-like middle stratosphere environment with radiation exposure, even as a spore
monolayer (106 spores/ml), i.e. with no self-shielding. Spore survival to space radiation and martian
conditions suggest that current planetary protection guidelines should be revisited integrating the high
resistance of fungal spores. Furthermore, A. niger colony growth and biofilm formation under simulated
microgravity was investigated. Scanning Electron Microscopy (SEM) pictures reveal never-before seen
ultrastructure of A. niger colonies and biofilms (i.e. vegetative mycelium embedded in extracellular
matrix). Results reveal changes in biofilm thickness, spore production and dry biomass, suggesting an
increased potential for A. niger to colonize spaceflight habitats. Lastly, P. rubens was proven as a model
organism for a spaceflight biofilm experiment aboard the International Space Station. Overall, this thesis
highlights the extraordinary resistance of fungal spores to extraterrestrial conditions and reveals their
ability to cope with spaceflight microgravity. This advocates for future research that will enable better
monitoring and controlling of fungal contaminations in space habitats, and that will help establish
filamentous fungi as valuable companions of human space exploration. | de |