HR: 15:25h
AN: P23B-08    [Abstracts]
TI: Environmental History and Stresses on Mars and Their Effect on Microbial Populations
AU: * Schulze-Makuch, D
EM: dirksm@wsu.edu
AF: Washington State University, Dept. of Geology, Webster Hall, Pullman, WA 99163 United States
AU: Diaz, B
EM: brd26@cornell.edu
AF: Cornell University, Dept. of Microbiology, Environmental Toxicology, Ithaca, NY 14853 United States
AU: Irwin, L N
EM: lirwin@utep.edu
AF: University of Texas at El Paso, Dept. of Biological Sciences, 500 W University Avenue, El Paso, TX 79968 United States
AB: We simulated the major environmental stresses on and near the Martian surface and recorded their effects on microbial populations of E. coli and D. radiodurans. Viability rates were determined for the populations under the single and combined stresses of sub-zero temperature, low-pressure, and UV radiation in salt-water soil and fresh-water soil at variable depths, and in sea water. Our results demonstrate that E. coli and D. radiodurans can remain viable under these exposure conditions, but are most sensitive to low pressure. The effect of low pressure is lessened under sub-zero temperatures as microbial populations from both species appear to respond synergistically to these combined stresses. However, the low-pressure effects are so dramatic (much more so than from UV radiation), that microbial life near the surface of Mars appears unlikely if it shares the characteristics of the model organisms in our study. This finding is consistent with our earlier projection that single cell life would, if extant near the surface, most likely be dormant. Results from the Mars Exploration Rovers and orbiters confirm a picture of Martian environmental history as consisting of long periods of quiescence with extremely slow surface erosion punctuated by short-duration episodes of quasi-stable conditions (e.g. triggered by magmatic driven activity at Tharsis) of a considerably wetter and warmer environment, which likely included hydrothermal activity and ponded surface water bodies in the northern plains (e.g. from cataclysmic floods). This environmental history would have promoted the (1) origin of life as chemoautotrophs, some of which may have evolved into heterotrophs, (2) possible origin of phototrophs, (3) strong directional selection for enhancing chemoautotrophy and the development of alternative energy sources, (4) strong directional selection for life cycles alternating between dormant and proliferative forms, and (5) possible persistence of some chemotrophs and organisms using alternative energy sources below the Martian surface to the present time. Putative microbes may thrive in ground water, which we would expect to differ substantially from ancestral forms.
DE: 4840 Microbiology
DE: 5705 Atmospheres--evolution
DE: 5749 Origin and evolution
DE: 6225 Mars
DE: 1800 HYDROLOGY
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting