Escherichia coli and Serratia liquefaciens, two common microbial spacecraft contaminants known to replicate under low atmospheric pressures of 25 mb, were tested for growth and survival in simulated martian conditions. Stressors of high salinity, low temperature, and low pressure were screened alone and in combination to determine how they might affect microbial activity. Growth and survival of E. coli and S. liquefaciens under low temperatures (30, 20, 10, or 5 °C) with increasing concentrations (0, 5, 10, or 20 %) of three salts believed to be present on the surface of Mars (MgCl2, MgSO4, NaCl) were monitored over 7 d. Results indicated higher growth rates for E. coli and S. liquefaciens at 30 and 20 °C and in solutions without salt or in 5 % concentrations. No increase in cell density occurred under the highest salt concentrations at any temperatures tested; however, survival rates were high, especially at 10 and 5 °C. Growth rates of E. coli and S. liquefaciens with and without salts at 1013, 100, or 25 mb of total atmospheric pressure were robust under all pressures. In a final experiment, E. coli was maintained in Mars-simulant soils in a Mars Simulation Chamber. Temperatures within the chamber were changed diurnally from -50 °C to 20 °C; UV light was present during daytime operation (8 hrs), and pressure was held at a constant 7.1 mb in a Mars atmosphere for 7 d. Results from the full-scale Mars simulation indicated that E. coli failed to increase its populations under simulated Mars conditions, but was not killed off by the low pressure, low temperature, or high salinity conditions. Escherichia coli, and potentially other bacteria from Earth, may be able to survive on Mars. Surviving bacteria may interfere with scientific studies or, if future conditions become more favorable for microbial growth, modify the martian atmosphere and biogeochemistry.
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd-4458 |
| Date | 01 January 2008 |
| Creators | Berry, Bonnie |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations |
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