Four-year bacterial monitoring in the International Space Station—Japanese Experiment Module “Kibo” with culture-independent approach

Studies on the relationships between humans and microbes in space habitation environments are critical for success in long-duration space missions, to reduce potential hazards to the crew and the spacecraft infrastructure. We performed microbial monitoring in the Japanese Experiment Module “Kibo”, a part of the International Space Station, for 4 years after its completion, and analyzed samples with modern molecular microbiological techniques. Sampling was performed in September 2009, February 2011, and October 2012. The surface of the incubator, inside the door of the incubator, an air intake, air diffuser, and handrail were selected as sampling sites. Sampling was performed using the optimized swabbing method. Abundance and phylogenetic affiliation of bacteria on the interior surfaces of Kibo were determined by quantitative PCR and pyrosequencing, respectively. Bacteria in the phyla Proteobacteria (γ-subclass) and Firmicutes were frequently detected on the interior surfaces in Kibo. Families Staphylococcaceae and Enterobacteriaceae were dominant. Most bacteria detected belonged to the human microbiota; thus, we suggest that bacterial cells are transferred to the surfaces in Kibo from the astronauts. Environmental bacteria such as Legionella spp. were also detected. From the data on bacterial abundance and phylogenetic affiliation, Kibo has been microbiologically well maintained; however, the microbial community structure in Kibo may change with prolonged stay of astronauts. Continuous monitoring is required to obtain information on changes in the microbial community structure in Kibo. A four-year study that monitored bacteria aboard the International Space Station (ISS) has discovered multiple species, mostly of human origin, living aboard. The research, by Masao Nasu and colleagues from Osaka University and the Japan Aerospace Exploration Agency, will help space agencies assess risks to astronauts during long-term spaceflight. The team found multiple types of bacteria lived on the Japanese Experiment Module of the ISS, named Kibo, despite it being disinfected weekly. Most bacteria were of human origin (e.g. gut microbes), which were likely transferred by the astronauts. A small proportion of bacteria was of non-human origin, such as Legionella, which the authors speculate arrived on resupply materials. Since microgravity can affect bacteria in unpredictable ways, such as increasing their virulence, tracking bacterial habitation in the ISS will provide insights for future space travel.