Abstract EANA2026-50

Background: The International Space Station (ISS) represents a highly unique, enclosed built environment. While the taxonomic composition of the ISS microbiome has been well-documented, the metabolic capacity of these communities, particularly the distribution of biosynthetic gene clusters (BGCs) across microbial taxa and station micro-niches, remains less well characterized. Mapping this functional landscape is critical for assessing microbial adaptation and crew health during long-duration spaceflight.

Methods: Public shotgun metagenomic datasets from the microbial tracking missions (MT-1 and MT-2) aboard the ISS were processed using the SqueezeMeta pipeline for co-assembly and binning. Taxonomic and pathway annotation, differential gene abundance, and BGC mapping—utilizing tools such as TaxiBGC—were integrated to compare microbial adaptive potential across distinct ISS locations. Location-specific differences in gene and pathway abundance were assessed, while high-quality metagenome-assembled genomes (MAGs) were used to link candidate adaptive traits and predicted BGCs to specific microbial populations.

Results: Our analysis reveals a robust, niche-stratified landscape within the ISS microbiome, where human commensals adapt dynamically to distinct spacecraft environments. First, we recovered 44 unique BGCs across the dataset, which mapped to at least 11 identified bacterial and fungal species. This biosynthetic landscape is heavily dominated by widespread human skin commensals, notably Cutibacterium acnes, Staphylococcus, and the fungus Malassezia. These core microbes encode a versatile survival toolkit, producing diverse antimicrobials, osmoprotectants (like ectoine), and radioprotective pigments (like melanin). Despite this consistent taxonomic presence station-wide, metabolic profiles diverged significantly across distinct ISS micro-niches, indicating localized environmental adaptation. Finally, MAG-resolved analyses revealed the specific mechanisms driving this site-specific persistence. Depending on their physical location, these microbes up-regulate targeted survival strategies, most notably heavy metal scavenging via localized siderophore production, multidrug efflux pumps, and dormancy systems.

Conclusion: These findings suggest that human-associated microorganisms on the ISS harbour location-dependent biosynthetic and adaptive potential. Integrated BGC, functional and MAG-resolved analyses identify candidate traits that may support persistence in spacecraft environments and inform future microbial monitoring.