山崎 丘

ABSTRACT The potable water dispenser (PWD) system plays a critical role as a source of drinking water for astronauts on the International Space Station (ISS). In this study, we examined the bioburden in the potable water produced by the PWD. The amount of extracellular polymeric substances (EPSs) in the PWD water was approximately 19 or 55 times greater than the bacterial count, and the EPS biomass accounted for approximately 24% or 86% of the bacterial biomass. Ralstonia pickettii consistently comprised approximately 70% or 80% of the bacteria for 3 years. Under simulated microgravity conditions, the isolated R. pickettii strains exhibited higher cell and EPS concentrations and higher total volume concentrations (average volume multiplied by concentration) of cell and EPS than under 1G conditions, whereas the average cell volume was smaller and the average EPS volume was larger. The ISS isolates showed higher EPS production and biofilm-formation abilities than terrestrial strains under nutrient-rich conditions and possessed high biofilm-formation ability comparable to those of terrestrial strains under nutrient-poor conditions. The ability of R. pickettii to produce EPS may play a crucial role in its adaptation to the water environment on the ISS. IMPORTANCE In space habitation environments, the use of recycled water is indispensable, and ensuring its microbiological safety is essential. In this study, we elucidated the microbiological characteristics of water from the potable water dispenser (PWD) on the International Space Station (ISS). Our findings revealed that bacteria of the Ralstonia pickettii are the predominant species in PWD water and that extracellular polymeric substances (EPSs) constitute a large proportion of the biomass. Furthermore, the isolated R. pickettii was shown to possess high EPS production ability and strong biofilm-forming capacity. Since EPS plays a crucial role in biofilm formation, these abilities may be important factors enabling R. pickettii to adapt to the water environment of the ISS.

Abstract The control of microbes in manned spaceflight is essential to reducing the risk of infection and maintaining crew health. The primary issue is ensuring the safety of a potable water system, where simultaneous monitoring of microbial abundance and community structure is needed. In this paper, we develop a flow cytometry-based counting protocol targeting cellular flavin autofluorescence as a tool for rapid monitoring of bacterial cells in water. This was successfully applied to estimate the bacterial bioburden in the potable water collected from the International Space Station. We also demonstrate the efficacy of the MinION nanopore sequencer in rapidly characterizing bacterial community structure and identifying the dominant species. These monitoring protocols' rapidity and cost effectiveness would contribute to developing sustainable real-time surveillance of potable water in spaceflight.

The International Space Station (ISS) is a completely closed environment that offers a long-term microgravity environment. It is a unique environment where microbes can fly and attach themselves to devices or humans, especially the exposed parts of the body and head. The ongoing monitoring and analysis of microbes and their movement inside the Japanese Experiment Module (named “Kibo”) of the ISS are intended to study the effects of microbes on humans and prevent health hazards caused by microbes during a long-term space mission. This paper describes the current status and future plan of Japanese microbiological experiments to monitor microbial dynamics in Kibo. It also describes the future prospective and prioritized microbiological research areas based on the “Kibo utilization scenario towards 2020 in the field of life science.” Given the microbial research in space being actively conducted by the USA, NASA and international activities are also reported.