In this report, we describe the initial colonization of environmental microorganisms associated with ISS on four different materials (Nomex, cable labeling material, printed circuit board and aluminum), which are commonly used at the ISS. Material substrates were placed in the Russian segment of the ISS in a ‘Target Book’ for 135 days. After the incubation, the ‘Target Book’ was analyzed on Earth by determining colony forming units and identifying the microorganisms by rRNA gene sequencing. The highest cell concentrations and widest biological diversity were on the polymer materials as Nomex and cable labeling material. Additional molecular biological identification revealed the following organisms as typical pioneer microorganisms: Staphylococcus spp., Bacillus spp., Streptococcus spp., Cladosporium spp., Sphingomonas spp., Micrococcus luteus and Stenotrophomonas maltophilia.
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