Starting with mission Apollo 16, the Gram-positive bacterium Bacillus subtilis has been
used in multitude of space experiments. Investigating the influence of extreme space conditions
like radiation, vacuum or microgravity, experiments with model organisms like B. subtilis, which
forms highly resistant endospores and biofilms, enlighten our understanding regarding
survivability, resistance and potential virulence in unfavourable habitats. Biofilms are organized
in a complex self-produced extracellular polymeric matrix commonly composed of
polysaccharides, proteins and nucleic acids. Building a biofilm protects the individual cell against
shear forces, chemicals (e.g. antibiotics or disinfectants), temperature changes and water as well
as nutrient depletion (Vlamakis et al., 2013, Cairns et al., 2014). The intrinsic resistance of
biofilms is challenging, not only in industry and medicine, but it can be problematic during
spaceflight conditions, especially for the crew as well as for the spacecraft. In particular, long
term missions with complex cooling systems, water supply and heat pipes may be vulnerable to
biofilm colonisation. In our work, we used a biofilm-forming B. subtilis strain and a biofilmmatrix
deficient mutant to study the impact of reduced gravity on maturated biofilms. Our
research aim is to compare biofilm formation in simulated microgravity (μg, using a fast-rotating
2D clinostat) to terrestrial gravity (1g) conditions by using different microscopic techniques.
White light profilometry, scanning and transmission electron microscopy (SEM, TEM) and
confocal laser scanning microscopy (CLSM) were used to analyse biofilms regarding their
topology and structure, respectively. Different types of survival experiments were conducted to
evaluate changes and resemblances due to the impact of microgravity. Our results show
qualitative architectural differences between simulated microgravity and 1g in cross-sections, but
no significant qualitative variations in biofilm surface topography. Our results show qualitative
architectural differences in cross-sections of biofilms grown in simulated microgravity and 1g
