Survey of environmental biocontamination on board the International Space Station

The International Space Station (ISS) is an orbital living and working environment extending from the original Zarya control module built in 1998. The expected life span of the completed station is around 10 years and during this period it will be constantly manned. It is inevitable that the ISS will also be home to an unknown number of microorganisms. This survey reports on microbiological contamination in potable water, air, and on surfaces inside the ISS. The viable counts in potable water did not exceed 1.0 × 10 ² CFU/ml. Sphingomonas sp. and Methylobacterium sp. were identified as the dominant genera. Molecular analysis demonstrated the presence of nucleic acids belonging to various pathogens, but no viable pathogens were recovered. More than 500 samples were collected at different locations over a period of 6 years to characterize air and surface contamination in the ISS. Concentrations of airborne bacteria and fungi were lower than 7.1 × 10² and 4.4 × 10¹ CFU/m³, respectively. Staphylococcus sp. was by far the most dominant airborne bacterial genus, whereas Aspergillus sp. and Penicillium sp. dominated the fungal population. The bacterial concentrations in surface samples fluctuated from 2.5 × 10¹ to 4.3 × 10⁴ CFU/100 cm². Staphylococcus sp. dominated in all of these samples. The number of fungi varied between 2.5 × 10 ¹ and 3.0 × 10⁵ CFU/100 cm², with Aspergillus sp. and Cladosporium sp. as the most dominant genera. Furthermore, the investigations identified the presence of several (opportunistic) pathogens and strains involved in the biodegradation of structural materials.