Abstract
Microorganisms' natural ability to live as organized multicellular communities - also known as biofilms - provides them with unique survival advantages. For instance, bacterial biofilms are protected against environmental stresses thanks to their extracellular matrix, which could contribute to persistent infections after treatment with antibiotics. Bacterial biofilms are also capable of strongly attaching to surfaces, where their metabolic by-products could lead to surface material degradation. Furthermore, microgravity can alter biofilm behavior in unexpected ways, making the presence of biofilms in space a risk for both astronauts and spaceflight hardware. Despite the efforts to eliminate microorganism contamination from spacecraft surfaces, it is impossible to prevent human-associated bacteria from eventually establishing biofilm surface colonization. Nevertheless, by understanding the changes that bacterial biofilms undergo in microgravity, it is possible to identify key differences and pathways that could be targeted to significantly reduce biofilm formation. The bacterial component of Space Biofilms project, performed on the International Space Station in early 2020, contributes to such understanding by characterizing the morphology and gene expression of bacterial biofilms formed in microgravity with respect to ground controls. Pseudomonas aeruginosa was used as model organism due to its relevance in biofilm studies and its ability to cause urinary tract infections as an opportunistic pathogen. Biofilm formation was characterized at one, two, and three days of incubation (37 °C) over six different materials. Materials reported in this manuscript include catheter grade silicone, selected due to its medical relevance in hospital acquired infections, catheter grade silicone with ultrashort pulsed direct laser interference patterning, included to test microtopographies as a potential biofilm control strategy, and cellulose membrane to replicate the column and canopy structure previously reported from a microgravity study. We here present an overview of the biofilm morphology, including 3D images of the biofilms to represent the distinctive morphology observed in each material tested, and some of the key differences in biofilm thickness, mass, and surface area coverage. We also present the impact of the surface microtopography in biofilm formation across materials, incubation time, and gravitational conditions. The Space Biofilms project (bacterial side) is supported by the National Aeronautics and Space Administration under Grant No. 80NSSC17K0036 and 80NSSC21K1950.