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Pseudomonas aeruginosa Growth and Exotoxin A Production in Static and Modeled Microgravity Environments. S. Guadarrama, E. deL. Pulcini, S.C. Broadaway, and B.H. Pyle, Dept. of Microbiology, Montana State Univ., Bozeman, MT.

Modeled Microgravity (MMG) systems are used to simulate the gravitational effects of spaceflight on cells. Previous studies have shown changes in protein expression in response to MMG in P. aeruginosa PA103 (ATCC 29260) bacteria. To assess the effects of MMG, the lag, log and stationary phases of growth of PA103 were studied using triplicate cultures grown in syringes containing Modified Simple Defined Medium 2, inoculated with frozen cultures and incubated at 37oC. Static incubation was compared with rotation at 15 RPM on a rotating drum (radius=6cm) or on a Clinostat. Growth was determined by reading optical density at 540 nm (OD) and R2A agar drop plate counts (PC). Exotoxin A (ETA) production was determined by an Enzyme-Linked Immunosorbent Assay (ELISA) technique. Mean PC at T0 was 6.7+0.3 log CFU/ml (OD 0.04+0.00). Results for the rotating drum showed that the log phase of growth started about 9h (Static PC=7.9+0.2, OD=0.14+0.05; MMG PC=7.6+0.1, OD=0.10+0.01). Stationary phase was reached at 15 h (Static PC=8.5+0.1, OD=0.50+0.01; MMG PC=8.3+0.3, OD=0.56+0.06) and continued through 24h (Static PC=8.5+0.1, OD=0.51+0.01; MMG PC=8.5+0.1, OD=0.56+0.03). Similar growth was observed with the Clinostat: OD was 0.3 (static) vs 0.34 (MMG) at 15 h, and 0.43 (static) vs 0.45 (MMG) at 24h. Corresponding PC were 8.4 vs 8.2 at 15h and 8.5 vs 8.6 at 24h. For the rotating drum trials, ETA (ng/ml) increased from 3.2 at T0 to 38ng/ml (static) vs 30ng/ml (MMG) at 9h, 240ng/ml (static) vs 250 (MMG) at 18h, and 119 (static) vs 145 (MMG) at 24h. There was a decline in cfu/ml of at least half a log and an increase in ETA production in both environments after the onset of stationary phase (18h). The results suggest that MMG under these conditions does not dramatically affect growth or ETA production of PA103.(Supported by NASA: NAS2-14263/NCC2-1143.)