Boreskov

PP‐46bacterial cultures, except Halomonas sp. Н8 at ‐70 °C had high CFU number; in only a singlecase of Halomonas sp. Н8 at ‐70 °C, CFU number decreased for 27%. At 200 g L ‐1 NaCl,freezing at ‐70 °C decreased CFU number for 8% to 97% in all cases, but complete extinctionwas not observed. The most dramatic growth depression was observed for Halorubrumstrains Н4 and Н7. The Н8, Н9, Н12, and Н13 strains had a high survival rate. The majority ofcultures successfully survived freezing at –18 °C: 0 to 40% decrease of CFU number wasdetected. Freezing at ‐70 °C at 300 g L ‐1 NaCl resulted in complete extinction of all cultures,while freezing at ‐18 °C led to extinction in six cases; CFU number decreased significantly inН3 and Н7 strains, and the Salicola sp. Н9 quantity didn’t change.Discussion. Halotolerant bacteria belonging to the Halomonas genus had the widestgrowth ranges. Growth optimums of bacterial strains were shifted towards smaller NaClconcentrations (100, 200 g L ‐1 ). Obligatory halophilic archeal strains had smaller growthranges and had growth optimum at 200‐300 g L ‐1 NaCl. Bacterial strains were more tolerantto different incubation temperatures. Archeal strains were less tolerant to freezing; the mostsignificant mortality was detected at ‐70 °C, which was earlier demonstrated for thehalophilic archeobacterium Natronorubrum sp. [4]. Judging from the results of ourexperiments, we can suggest that these are not halophilic archea but halotolerant bacteriathat could be the analogs of Martian organisms, since they can survive wide mineralizationranges and low temperatures with the lowest decline of viability. In earlier studies, theeffects of different stress conditions have been tested on several microorganisms from thebacterial domain with various ecological properties [3]; in this study we demonstrated a highsurvival potential of halotolerant bacteria, which makes them likely candidates for life onearly Mars. We are planning to present an additional experiments with lower organiccontent in the solution and adding of perchlorates and sulfates. Also the impact of lowatmospheric pressure and ionizing radiation on survival of halotolerant bacteria will bestudied by simulation experiments.The financial support by Integration Project 10 of the Siberian Branch of RAS, RFBR 11‐05‐00717 is gratefully acknowledged.Literature[1]. Litchfield C.D. Meteoritics and Planetary Science, Vol. 33, Is. 4, p. 813‐819, 1998[2]. Taylor G. J., Boynton W. V., McLennan S. M. et al. Geophys. Res. Lett., Vol. 37, Is. 12, CiteID L12204, 2010[3]. Kounaves S. P., Hecht, M. H., Kapit J. et al. Geophys. Res. Lett., Vol. 37, Is. 9, CiteID L09201, 2010[4]. Peeters Z., Vos, D., ten Kate I. L. et al. Advances in Space Research, Vol. 46, Is. 9, p. 1149‐1155, 2010218