30-04-P. Lower Limits of Life on Mars: The Interactive
Effects of High Salinity, Low Temperature, and Low
Pressure on Two Common Biological Spacecraft
Contaminants in Simulated Martian Conditions
Bonnie J. Berry1 (bberry@mail.ucf.edu), David G. Jenkins1,
Andrew C. Schuerger2

1Department of Biology, University of Central Florida, USA,
2Department of Plant Pathology, University of Florida, USA

Conditions for bacterial growth and survival are well-known, but little
is known on potential bacterial growth and survival in extreme conditions
of Mars. This study tested for growth and survival of two common
biological spacecraft contaminants (Escherichia coli and Serratia
liquefaciens) in conditions representing martian soils (high salinity, low
temperature, and low pressure conditions, singly and simultaneously).
In experiment 1, E. coli and S. liquefaciens were cultured at low temperatures
in 0, 5, 10 and 20% concentrations of three salts (MgCl2,
MgSO4, NaCl). In experiment 2, E. coli and S. liquefaciens were exposed
to atmospheric pressures of 25, 100, and 1013 mb. In experiment
3, E. coli was grown in Mars-simulant soils in a chamber where diurnal
temperatures fluctuated from 50°C to 20°C, daytime included intense
UV light, and pressure was a constant 7.1 mb in a Mars gas mix
atmosphere. Each experiment ran one week. As expected, E. coli and
S. liquefaciens populations did not grow in highly saline, cold environments.
However, survival rates were high for both species in some
experimental conditions. Interestingly, low pressure alone did not negatively
effect growth. E. coli exhibited up to 35% survival in the fullscale
Mars simulation after one week. Results of this study suggest that
bacterial contaminants of spacecraft already landed on Mars may survive
to affect scientific studies of Mars and planetary biogeochemistry,
especially if episodic growth is also possible. Planetary protection and
future human exploration of Mars should carefully account for potential
bacterial contamination.