Exposure of microorganisms to simulated extraterrestrial space ecology.

Spores of five test organisms, Bacillus subtilis var. niger, Bacillus megaterium, Bacillus stearothermophilus, Clostridium sporogenes and Aspergillus niger and soils were exposed, while under ultra high vacuum to temperatures of from -190 degrees C to +170 degrees C for 45 days. Up to a temperature of 25 degrees C no loss in viability of the test spores were noted when compared to original populations maintained at room temperature at atmospheric pressure over a desiccant. At elevated temperatures differences in resistivity occurred so that at 88 degrees C only B. subtilis var. niger and A. niger survived in appreciable numbers. At 107 degrees C only A. niger spores survived, but none were recoverable after exposure to 120 degrees C. In comparison B. subtilis var. niger survived at atmospheric pressure and 90 degrees C for 5 days while none of the other spores were viable after 48 hours. Four groups of organisms in soil, mesophilic aerobes and anaerobes, molds and actinomycetes were similarly tested in the vacuum chamber. From one soil sample only actinomycetes survived 120 degrees C, whereas one other soil sample yielded viable bacteria after exposure to 170 degrees C. The resistance of the isolates to high temperatures in the absence of soil is being evaluated. Several organisms have been found to resists 120 degrees C in ultra-high vacuum for 4-5 days, and experiments at higher temperatures are in progress. When irradiated with gamma rays from a cobalt-60 source, there was a difference between vacuum dried test spores irradiated while still under vacuum to those exposed to air immediately before irradiation. A reduction of from one-third to one-ninth of the viability of spores irradiated in vacuum occurred with vacuum-treated spores irradiated in air.