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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 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.