Abstract
BackgroundThe built environment of the International Space Station (ISS) is a highly specialized space in terms of both physical characteristics and habitation requirements. It is unique with respect to conditions of microgravity, exposure to space radiation, and increased carbon dioxide concentrations. Additionally, astronauts inhabit a large proportion of this environment. The microbial composition of ISS particulates has been reported; however, its functional genomics, which are pertinent due to potential impact of its constituents on human health and operational mission success, are not yet characterized.MethodsThis study examined the whole metagenome of ISS microbes at both species- and gene-level resolution. Air filter and dust samples from the ISS were analyzed and compared to samples collected in a terrestrial cleanroom environment. Furthermore, metagenome mining was carried out to characterize dominant, virulent, and novel microorganisms. The whole genome sequences of select cultivable strains isolated from these samples were extracted from the metagenome and compared.ResultsSpecies-level composition in the ISS was found to be largely dominated by Corynebacterium ihumii GD7, with overall microbial diversity being lower in the ISS relative to the cleanroom samples. When examining detection of microbial genes relevant to human health such as antimicrobial resistance and virulence genes, it was found that a larger number of relevant gene categories were observed in the ISS relative to the cleanroom. Strain-level cross-sample comparisons were made for Corynebacterium, Bacillus, and Aspergillus showing possible distinctions in the dominant strain between samples.ConclusionSpecies-level analyses demonstrated distinct differences between the ISS and cleanroom samples, indicating that the cleanroom population is not necessarily reflective of space habitation environments. The overall population of viable microorganisms and the functional diversity inherent to this unique closed environment are of critical interest with respect to future space habitation. Observations and studies such as these will be important to evaluating the conditions required for long-term health of human occupants in such environments.
Highlights
The built environment of the International Space Station (ISS) is a highly specialized space in terms of both physical characteristics and habitation requirements
The ecology of indoor environments with continuous human contact is of great interest due to potential impact on human health; this is of particular concern in built environments that are spatially confined with long-term human occupants [3, 4]
Sample characteristics Materials collected from three sample types examined as part of this study included the following: ISS filter particles obtained from high-efficiency particulate arrestance (HEPA) systems onboard the space station (ISS filter), ISS dust samples obtained through vacuum collection within the cabin (ISS dust), and dust samples obtained through vacuum collection from a cleanroom where spacecraft are assembled (SAF dust)
Summary
The built environment of the International Space Station (ISS) is a highly specialized space in terms of both physical characteristics and habitation requirements. The ecology of indoor environments with continuous human contact is of great interest due to potential impact on human health; this is of particular concern in built environments that are spatially confined with long-term human occupants [3, 4] These environments are typified by enclosures associated with extraterrestrial habitation. Recent examination of microbial content associated with astronauts has explored the degree to which the human microbiome adjusts to habitation within the ISS [11, 12]. Implications of these data for maintenance of crew health are critical when evaluating design and maintenance of this highly specialized built environment [6]
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