Analysis of bacterial profiles on skin of AGBRESA participants – a study concerning terrestrial astronauts under simulated microgravity

Abstract

The International Space Station (ISS) is a unique habitat and can be considered as humanmade, confined environment. The station is continuously inhabited by humans over 20 years and, thus, has developed its own microbiome primarily shaped by astronauts. Through longterm space missions, humans experience numerous harmful impacts like microgravity. The reduced gravity leads to physiological adaptation that includes redistributed tissue fluids towards the upper body. Alongside this process, skin physiological parameters simultaneously alter, resulting in frequent medical skin incidences. Because human skin microbiota is essential for intact skin barrier function, this could play a key role in the health state of our largest organ and composition of the ISS microbiome. The aim of this thesis was to investigate correlations between altered skin physiological parameters due to simulated microgravity and bacterial profiles. Regarding the compromised immune state and biodegrading microbes coming from humans, a detailed monitoring of skin microbiota is necessary to develop appropriate countermeasures. For this purpose, the Artificial Gravity Bedrest study with ESA (AGBRESA) provided a suitable platform. The first campaign of AGBRESA investigated 12 test subjects who for 60 days experienced 6° headdown-tilt in order to simulate fluidic shifts as in space. Swab samples from skin were taken and the parameters sebum, moist, and pH were measured with dermatological probes. This work revealed a significant enrichment of lipophilic Cutibacterium (formerly Propionibacterium) and Corynebacterium induced by artificial microgravity while sebum and water accumulation on skin were increased. Similar results were also found from data of astronauts under real space conditions. Additionally, Pseudomonas was identified as the responsible pathogen involved in ear related infections during head-down-tilt while cohabitation of Staphylococcus in the healthy ear was detected. Each test subject showed individual bacterial community compositions. Thus, these data could be a step towards individualized medicine as countermeasure. The obtained results and experiences from this study lay the foundation for future projects that focus on human-associated microbiome monitoring.