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Strategies for the inoculation of bioreactors for long-term space missions include communities of diverse composition or, alternatively, communities of a few organisms selected for their ability to efficiently catalyze reactions of interest in the reactor. The concept of functional redundancy states that in a diverse community, several different organisms may be present that are capable of effecting processes necessary to the maintenance of the system function. The concept implies that if some members of the community are lost, others will be able to keep the system from failing in the critical reactions that take place therein. In a sewage reactor in the laboratory, a diverse community at steady state was perturbed by elimination of aeration for seven days. Chemical pools (NH4+, NO3-, dissolved O2), pH, and CO2 evolution were monitored before, during, and after the perturbation.

Airborne and surface microbiological sampling was performed on the pressurized Multi-Purpose Logistics Module “Raffaello” (MPLM-6) that serviced the International Space Station (ISS) on NASA Return to Flight mission ISS LF-1/STS-114. In September of 2005, aerosol samples and surface samples were collected from the MPLM at the Kennedy Space Center prior to locker de-stow and module de-integration. Analyses of the culturable bacterial count from selective and non-selective media showed low microbial densities (>100 CFU per sq m) in the MPLM surface samples collected from air filtration ducts and other hardware surfaces. Isolates identified included diverse representatives of the gram-negative and gram-positive bacteria as well as common airborne fungi. Although aerosol bio-burden samples plated onto non-selective media were below detection limit in microbial density (<1 CFU per 500 L), bacterial and fungal populations were detected in surface swab samples.

The inclusion of bioregenerative life support elements (i.e., plant growth systems and bioreactors) will significantly increase the total abundance of microorganisms in extraterrestrial facilities. If the microbial communities associated with these systems (e.g., biofilms attached to plant roots or hardware surfaces) serve as reservoirs for potentially pathogenic human-associated bacteria, then bioregenerative systems may represent a human health risk. Research at the Kennedy Space Center during the past several years has attempted to quantify this risk by assessing the capacity of different human-associated bacteria to survive in prototype ALS systems.