Characterization of Bacteria from the International Space Station Drinking Water
From a microbiology perspective, the International Space Station (ISS) is interesting considering its microgravity, increased radiation, low humidity and elevated carbon dioxide levels. Because of its isolation, and unique environment, it is vital to study the microorganisms that thrive there to ensure the safety of the astronauts aboard. We refer to the collection of microbes in an environment a microbiome. Understanding the microbiome of the ISS is vital to astronaut health and long term mission viability.
With Sloan Foundation and J. Craig Venter Institute (JCVI) funding, Aubrie O’Rourke, Ph.D. and her team examined the microbes found within the ISS potable water system (PWS). The PWS in combination with the potable water dispenser (PWD) is a water recycling system that utilizes physical and chemical techniques to filter, decontaminate, and sterilize water used for drinking and food hydration.
Microbial surveillance of the PWS was implemented by NASA to ensure crew health. These surveillance efforts, which use standard culturing techniques, have been conducted over twelve years and 22 missions, beginning shortly after the PWD was launched in late 2008.
Throughout surveliance, the closely related organisms, Burkholderia cepacia and Burkholderia contaminans (both genomovars of the Burkholderia cepacia complex — BCC), have been frequently cultured from the PWD. Burkholderia species are known to propagate in a variety of environments, including within human host cells. Representatives of these species are considered opportunistic pathogens.
The antibiotic resistance and intracellular survival capabilities of BCC members make them resistant to many therapeutics. Burkholderia spp. are known to withstand disinfection and sterilization procedures as they display a moderate to high-tolerance to stress such as UV-C radiation, antibiotics, and high heavy-metal concentrations.
They are also known to survive long periods in distilled water. This ability to survive in distilled water with minimal additives has made them problematic for healthcare, as hospital-acquired BCC infections can arise from contaminated disinfectants, anesthetic solutions, distilled water, and aqueous chlorhexidine solutions.
Dr. O’Rourke and her team found that isolates for both species, B. cepacia and B. contaminans recovered from the ISS PWD had highly similar genomes regardless of isolation date. This suggests that each population likely stemmed from two distinct founding strains that were implanted during assembly of the PWD on Earth prior to transport to the ISS.
Based on phenotypic analyses (observable characteristics), it seems likely that the two populations of Burkholderia found are not becoming more virulent than those that might be encountered here on Earth, yet they do maintain a baseline of virulence.
This work, in the context of space life-support engineering, demonstrates that is not quite enough to say that the water is safe-for-human consumption because it harbors an arbitrary amount of bacteria deemed safe, but instead it is critical to understand what bacteria are found there.
Scientists assisting Dr. O’Rourke in this study included 11 UC San Diego senior engineering design students, JCVI professors Drs. Chris Dupont and William Nierman, and NASA Ames scientists Drs. Michael Lee and Craig Everroad.