Astrobiological relevance of skin-associated bacteria: Resistance of Staphylococcus capitis to spaceflight conditions

Abstract

Understanding the survival of bacteria in space environments is crucial for assessing potential risks in space exploration missions, particularly concerning astronaut health, life detection and planetary protection. Bacteria from the human microbiome, like the skin microbiome, are important as they will inevitably be present in human space missions to other celestial bodies. For example, Staphylococcus capitis, a commensal skin bacterium, has been frequently isolated from the International Space Station and spacecraft assembly facility clean rooms. Previous studies have shown that spaceflight-specific conditions can induce changes in bacterial physiology and resistance behaviour, such as increased expression of virulence factors, differences in biofilm formation, and decreased susceptibility to antibiotics. This study compared three spaceflight-associated strains of Staphylococcus capitis to the type strain to investigate the physiological and genomic changes induced by spaceflight-relevant conditions. The strains were assessed for growth, colony morphology, metabolism, biofilm formation, and susceptibility to antibiotics. Additionally, their survival under various stress conditions, including treatment with hydrogen peroxide, desiccation, X-ray irradiation, and UV-C exposure, was examined. Genomic analysis was conducted to identify genetic determinants of phenotypic differences. While all strains exhibited similar metabolic patterns, antibiotic sensitivity and radiation tolerance, we observed minor physiological differences among them. These differences were primarily compared with the type strain, with only minor differences observed among the other three strains. The S. capitis isolate from the ISS displayed an enhanced growth rate and delayed yellow colony pigmentation. The same yellow pigmentation was also detected in an S. capitis isolate from a 60-day bed rest study in which human subjects lay in a 6° head-down tilt to mimic the body weight unloading and fluid shifts experienced by astronauts in microgravity. The phenotypic and genomic variances observed between the strains in this study do not suggest an increased virulence of the spaceflight isolate compared to the other strains. Overall, the findings indicate that S. capitis has a high tolerance to spaceflightrelevant conditions such as ionising radiation and desiccation. This emphasises the need for further exploration of the resistance mechanisms of human-associated microorganisms to spaceflightContact: eana-web@eana-net.eu | Data protection | © 2025 European Astrobiology Network Association (EANA) conditions and adaptation of appropriate contamination mitigation strategies if required.