Increased Relative Humidity Promotes Abundance of Potentially Harmful Microbes in Dust Samples Aboard the International Space Station

Abstract

Astronaut health aboard the International Space Station (ISS) is of great concern as space travel becomes more frequent. Environmental conditions aboard the ISS significantly influence microbial communities, which pose potential risks to astronaut health and spacecraft integrity. This study investigates the effects of varying relative humidity (RH) levels on the diversity, composition, and predicted interactions of microbial communities in ISS dust samples. This builds on the hypothesis that dust samples obtained from the ISS will demonstrate greater pathogenic bacterial growth and more significant predicted interactions at higher RH compared to lower RH. Using data from Nastasi et al., microbial diversity was analyzed across low, medium, and high RH conditions. High RH decreased alpha diversity, indicating reduced richness and evenness, and altered beta diversity, showing distinct microbial community compositions compared to low RH. Furthermore, core microbiome analysis was used to identify Staphylococcus as a taxa that remains constant across all RH levels, signifying the large fluctuations of other populations due to RH conditions. To elucidate these populations, differential abundance analysis showed that high RH selectivity promotes potentially pathogenic taxa such as Streptococcus and Anaerococcus. Due to the significant abundance of such taxonomy groups, their interactions with other organisms were determined for the different RH conditions. Our findings suggest that high RH disrupted significant microbial community interactions, and only promoted the prevalence of some specific microorganisms. Despite these findings, we observed that significant interactions between potentially pathogenic microorganisms can occur under low and medium RH conditions. These findings suggest that increasing RH conditions promotes the growth of specific bacteria that favour this environment, while decreasing the overall diversity of the microbial communities. We also highlight that fewer pathogenic interactions occur at lower RH conditions.