Biofilm formation and stress response of space flight relevant Staphylococcus capitis isolates

Prolonged human space flight requires methods for sustaining the health and safety of the crew. During space travel, exposure to microgravity, radiation, and stress triggers a multitude of adaption reactions not only in the human body but as well in the associated microbiome. It is not clear yet which influence this might have on the astronaut’s health. Studies have shown before that space flight has an influence on bacterial virulence. Biofilm formation and pigmentation are such virulence factors, whereby their expression during space flight still needs further investigation. Pigments possess antioxidant properties, which increase bacterial resistance to oxidative but also to osmotic stress. Biofilms can cause damage to space flight equipment and are difficult to eliminate due to their increased resistance to antibiotics and disinfectants. In previous experiments, significant differences that included colony pigmentation, increased growth, and tolerance to desiccation were observed between two strains of Staphylococcus capitis subsp. capitis – an ISS isolate K1-2-2-23 and the DSMZ type strain DSM 20326. In this project, further characterization of both strains with seven additional strains of S. capitis subsp. capitis were carried out to investigate potential peculiarities within the ISS isolate compared to the other strains and to assess the potential influence of space conditions. Besides the evaluation of morphology, metabolism and growth, the focus was put on biofilm formation and stress responses of the individual strains. Stress was induced by desiccation, irradiation and osmotic stress. In the course of this work, two pigmented strains were identified, whereby possible correlations of pigmentation with the obtained results were discussed. Pigment producing strains K1-2-2-23 and H17 revealed higher tolerance to desiccation as well as to exposure to H₂O₂ compared to remaining strains. Irradiation with 100 Gy revealed slight decreases within the cell number, but the effect was not substantial. The BATH assay, which predicts cell hydrophobicity, indicated cells of DSM 20326 to be significantly more hydrophobic compared to remaining strains, despite the fact of K1-2-2-23 being a strong biofilm former. Biofilms should be further investigated by analyzing the biomass, structure and matrix components. Furthermore, following studies should focus on correlation between pigmentation and high tolerances in stress conditions, such as high radiation doses or oxidative stress. Pigments in bacteria may additionally serve to stabilize membranes as well as to resist external stressors and host induced stress. Therapeutic interventions for pigment producing bacteria could include substances that inhibit pigment production