RESUMO
The main factor limiting growth of terrestrial organisms under Martian conditions is the low humidity; therefore the biology of xerophytic micro-organisms has been studied. We found earlier that Bacillus megaterium var. halotolerant and Mycococcus ruber could survive and grow under Martian conditions. In this work, we studied the zone of tolerance of these and some other micro-organisms towards various levels of water activity, and the toxicity of substances which were used to control this activity. A technique for quantitative evaluation of the xerophytic nature of micro-organisms is proposed. The technique is based on quantitative evaluation by gas chromatography of carbon dioxide evolved in the course of growth of micro-organisms on media with different values of water activity.