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For over 40 years, NASA has been putting humans safely into space in part by minimizing microbial risks to crew members. Success of the program to minimize such risks has resulted from a combination of engineering and design controls as well as active monitoring of the crew, food, water, hardware, and spacecraft interior. The evolution of engineering and design controls is exemplified by the implementation of HEPA filters for air treatment, antimicrobial surface materials, and the disinfection regimen currently used on board the International Space Station. Data from spaceflight missions confirm the effectiveness of current measures; however, fluctuations in microbial concentrations and trends in contamination events suggest the need for continued diligence in monitoring and evaluation as well as further improvements in engineering systems. The knowledge of microbial controls and monitoring from assessments of past missions will be critical in driving the design of future spacecraft.

Microgravity elicits different responses from various microorganisms and may alter the population dynamics of a microbial community. Four isolates from a hydroponic study were combined in experimental communities cultured in 50-mL high aspect-ratio rotating-wall vessel bioreactors (HARVs) for 10 days under either simulated microgravity (SMG) or control (1.004×g) conditions. Pseudomonas azelaica maintained a population density just above 1×109 CFU/mL in all treatments, but exhibited an increased percentage of a crinkled colony morphology in SMG. Abundance of Rhodotorula rubra was unaffected by either SMG or a 4-strain mixed culture environment alone; however, in a 4-strain community cultured under SMG, density of R. rubra dropped by more than two orders of magnitude. Interactive effects between SMG and presence of Pseudomonas seemed to inhibit growth of R. rubra. These interactive effects were not predictable from separate study of the components of the system.

Bioregenerative components for advanced life support (ALS) systems will need to be reliable and stable for long-duration space travel. To examine the stability and resilience of microbial communities that recover nutrients from inedible wheat residues, we maintained 4 bacterial strains in mixed communities for 7 weeks. After 3 weeks of incubation, aeration was stopped for several days. Although the abundance of each isolate declined during the perturbation, all strains persisted throughout the experiments. However, only 80% of functions lost during perturbation were recovered afterward. Thus, persistence of strains in a community did not guarantee the persistence of metabolic functions which those strains could perform. Niche partitioning of the heterogeneous molecules in the wheat residue apparently contributed to stable coexistence of the 4 strains.

The first two phases of the Lunar-Mars Life Support Test Project [LMLSTP] involved housing human volunteers in closed chambers that mimic future extraterrestrial life support systems. The Phase I test involved one person living for 15 days in a chamber with wheat as the primary means of air revitalization. The Phase II test involved 4 people living for 30 days in a chamber with physical/chemical air revitalization and waste water recycling. The consequences of closure on microbial ecology and the influence that microbes had on these closed environmental life support systems were determined during both tests. The air, water, and surfaces of each chamber were sampled for microbial content before, during, and after each test. The numbers of microbes on the Phase I habitation chamber surfaces increased with length of occupation.

The ability of the water recovery system (WRS) designed for Phase II of the Lunar-Mars Life Support Test Project to remove viral contaminants was tested by challenging the system with bacteriophages MS-2 and PRD-1. Urine-pretreatment and ultrafiltration/reverse osmosis (UF/RO) steps each reduced the combined density of both bacteriophages from >109 to <1 Plaque-Forming Units (PFU)/100 mL. UF/RO also reduced the bacterial density from 108 to 107 Colony-Forming Units (CFU)/100 mL. Before UF/RO, the predominant species of bacteria in the water were Acinetobacter calcoacetious and Klebsiella pneumoniae; afterward, the predominant species were Burkholderia cepacia and B. picketti. The removal of the bacteriophages and the difference in predominant bacteria across the UF/RO step suggest that the Burkholderia had been established downstream of the UF/RO membranes before the test began.

Space Station Freedom offers an opportunity to study in depth the long-term effects of microgravity on the basic biology of animals and plants, an area of great importance to the permanent presence of man in space. NASA has long recognized the significance of spaceflight research using non-human biospecimens in understanding these broad aspects of gravitational biology. To this end, plants and small animals have flown on manned and unmanned missions since 1965, including the highly successful Spacelab Life Sciences-1 (SLS-1) mission in June 1991. To minimize the potential for problems related to the inflight exchange of microbes between crew members and research biospecimens, NASA has established a policy of microbiological certification of animals designated to fly on NASA manned missions. The Human Research Policy and Procedures Committee at the Johnson Space Center administers this policy.

A microelectrode-based electrochemical detection method was used for quantitation of bacteria in water samples. The redox mediator, benzoquinone, was used to accept electrons from the bacterial metabolic pathway to create a flow of electrons by reducing the mediator. Electrochemical monitoring electrodes detected the reduced mediator as it diffused out of the cells and produced a small electrical current. By using a combination of microelectrodes and monitoring instrumentation, the cumulative current generated by a particular bacterial population could be monitored. Using commercially available components, an electrochemical detection system was assembled and tested to evaluate its potential as an emerging technology for rapid detection and quantitation of bacteria in water samples.

A comprehensive microbiological facility is being designed for use on board Space Station Freedom (SSF). Its purpose will be to conduct microbial surveillance of the SSF environment and to examine clinical specimens. Air, water, and internal surfaces will be periodically monitored to satisfy requirements for a safe environment. Crew health will remain a principle objective for every mission. This paper will review the Microbiology Subsystem capabilities planned for SSF application.