N-143. Bacterial Growth at Concentrations of Magnesium Sulfate Found in Martian Soils

J. D. Crisler, T. M. Newville, M. A. Schneegurt;
Wichita State Univ., Wichita, KS.

The Great Salt Plains (GSP) located near Cherokee, Oklahoma is a barren unvegetated salt flat, where Permian brine rises to the surface and evaporates under arid conditions, leaving a salt crust. Halophilic microbes thrive under these desiccating conditions with high salinities, basic pHs, inexorable exposure to solar UV radiation, and immoderate temperatures. Recent evidence has shown that Mars has cold, hypersaline, acidic, desiccated soils, that in the past were likely wetter. Some Martian soils are rich in magnesium sulfate. Halophilic bacteria from places like the GSP, may be able to tolerate these high levels of magnesium sulfate, and thereby represent a forward contamination hazard for robotic explorers to Mars. Spacecraft assembly buildings are typically dry, and halophilic bacteria related to GSP isolates are found there. Previous studies at the GSP have generated a microbial collection of more than 100 halotolerant isolates representing over 40 phylotypes, rich in Halomonas and Bacillus species. As little is known about bacterial survival at extremely high magnesium sulfate concentrations, the growth of a collection of GSP bacterial isolates was measured, at different concentrations of MgSO4 and at different temperatures. Many isolates (24%) grew at 2M MgSO4 with 1% NaCl at 25 °C, with fewer (6%) growing with 10% NaCl. At 7 °C, 15% of the isolates that grew at 25 °C showed some growth at high MgSO4 concentrations. Isolates capable of growth at 2M MgSO4 were tested for tolerance to freeze-thaw cycles; frozen overnight at -80 °C in an ethanol bath and then thawed at 25 °C while in the bath. Serial dilution on 10% salinity plates was used to measure survival after each freeze-thaw cycle. The results indicate that halophilic bacteria from the GSP can tolerate high levels of MgSO4 with extremely fluctuating temperatures. Therefore, forward contamination of Mars by terrestrial bacteria may be possible. This work was supported by NSF Microbial Observatories and NIH K-INBRE funding.