On the multiplication of xerophilic micro-organisms under simulated Martian conditions

The environmental conditions prevailing on Mars would supposedly favour the existence there of micro-organisms belonging to xerophiles, anaerobes, or micro-aerophiles, oligonitrophiles, which are able to grow in wide temperature intervals. From soil samples taken in deserts and tundra, antarctic halophilic bacteria, able to grow in liquid media containing 20-25% of sodium chloride, were isolated. Some of these cultures appeared to be also osmophilic (growth on media with 50% glucose); they grew at temperatures from 5 degrees C to 50 degrees C, and developed on media without a nitrogen source (oligonitrophiles). Of special interest was the halophilic and osmophilic form of Bacillus megaterium isolated from the Nubian desert. In experiments with this bacterium the following technique was used. A thin film of potato extract agar was prepared on a glass slide and dried over a saturated K2SO4 solution in a closed container up to the level of maximal hygroscopic moisture. The cell suspension was then sprayed on to the agar surface, the film dried again at 45 degrees C, and the glass slide put in the test tube over the saturated solution of K2SO4. The test tube was evacuated, flushed three times with a gas mixture containing 80% CO2 plus 20% Ar, and sealed. Under these conditions the water content of the agar film was equal to the maximal hygroscopic moisture; only the xerophilic form of bacteria are able to develop at this moisture level. This halophilic strain of Bac. megaterium grew satisfactorily under these conditions, as did a halophilic and osmophilic strain of Mycococcus ruber isolated in Antarctica. Both the halophilic strain of Bac. megaterium and that of M. ruber were able to grow under simulated Martian conditions. Xerophily and halophily may be linked. This assumption was supported by relatively high incidence of xerophilic forms among halophilic bacteria isolated from different soils of both high and low salt content as well as from salty muds.