Microbial Burden of Drinking Water Aboard the Space Shuttle and International Space Station

103rd General Meeting of the American Society for Microbiology
May 18-22, 2003, Washington, DC

For more information on any presentation at the 103rd General Meeting of the ASM contact Jim Sliwa, ASM Office of Communications at jsliwa@asmusa.org

EMBARGOED UNTIL: Monday, May 19, 1:00 p.m. EDT

(Session 78, Paper N-061)

Myron La Duc
NASA Jet Propulsion Laboratory
Pasadena, CA, United States
Phone: 818-354-8271

Monitoring the microbial diversity and overall bio-burden of International Space Station drinking waters is of utmost significance to astronaut health. Recommendations on how to minimize the numbers of microorganisms that are present and/or how to remove any opportunistic pathogens are practical applications of such research. We analyzed water samples collected directly from the ISS for microbial bioburden. We attempt to answer several questions regarding the water that astronauts drink while in space. Which bacteria are present in the water, and in what concentrations? Do these bacteria in any way pose a threat to the health of astronauts? How and where are these bacteria gaining access into the drinking water system?

This work was performed as a collaborative effort spanning three NASA centers. Work relating to this project was performed at the Jet Propulsion Laboratory, Johnson Space Center, and Kennedy Space Center. This molecular microbial study on the ISS drinking water was funded by a grant from the NASA Advanced Environmental Monitoring and Control (AEMC) program and is being presented at the 103rd General Meeting of the American Society for Microbiology, Washington D.C., May 18-22, 2003.

Drinking water intended for the STS-113 mission aboard the Endeavor OV-105 shuttle, as well as the International Space Station (ISS), was characterized for microbial contamination using conventional and molecular techniques. The city of Cocoa's municipal water, ultimately to be consumed by astronauts aboard the ISS, is treated with iodide biocide at KSC and pumped into the space shuttle. Upon arrival at the ISS, this water, together with fuel cell generated water, is transferred to portable storage containers until consumed by astronauts at a distribution system designated SVO-ZV. Humidity condensate is also processed for consumption in a regenerative system designated SRV-K.

This study confirmed the effectiveness of the KSC biocide treatment in removing all cultivable microbes from the drinking water. Untreated municipal water samples contained 1.4x104 CFU/100 mL by conventional plate count analysis, where as ATP-based detection methods showed 1.3x105 microorganisms present, an order of magnitude higher. The regenerated water used for food rehydration in the ISS (SRV-K hot) had 5.1x101 CFU/100 mL cultivable counts. However, the water collected from the SVO-ZV did not reveal any measurable microbial counts. It is interesting to note that both culture and DNA-based methodologies reported the presence of Acidovorax temperans, a halogen (biocide) reducing bacterium, from the SRV-K hot water sample.

Molecular microbial community analyses showed bacterial species phylogenetically affiliated with alpha and beta proteobacteria for the municipal water prior to biocide treatment, while only gamma-proteobacteria sequences were seen following treatment. Several 16S rDNA sequences related to opportunistic pathogens, such as Afipia, Deftia, Propionibacterium, and Ochrobactrum, were retrieved from the ISS water samples. This study has not yet confirmed the presence of active pathogens in the drinking water, however, evidence strongly suggests that implementation of new cultivation approaches to identify the presence of pathogens is essential in accurately assessing inherent health risks to ISS astronauts.

In lay terms, our study suggests no reason for alarm or concern, but brings to attention the seriousness of the matter. Astronauts are under constant stresses in space, which they are not accustomed to here on earth, oftentimes even entering into immuno-compromised states. Retrieving DNA sequences from opportunistically pathogenic bacteria from the drinking water is not a finding to ignore, rather continue to monitor and delve further into why such microbes are present, and what can we do to minimize/eliminate their presence.