Experiments with thawing samples of permafrost sediments showed that long term freezing in nature make bacteria active to more extent in comparison with bacteria of tundra soils and rapid increase in number of viable bacteria after thawing was detected earlier in permafrost samples (in first hour after melting), than in tundra soils,

Studies on growth and structure stability of permafrost bacteria in relation to freezing and thawing processes demonstrated that species survived in permafrost deposits are cold tolerant forms that showed further cold adaption.

Numerous cycles of freezing and thawing of indigenous microbes directly in the samples of tundra soil and permafrost sediments revealed various responses of microbial communities. In the most samples of syncryogenic deposits where microbes underwent similar stress conditions in nature only little changes in composition of dominating species and number of viable cells were detected in comparison with tundra soil and sediments which never experienced thawing process.

Investigation of repeated 30 cycles of freezing and thawing on ultra structure and survival of bacterial strains, that were recovered from permafrost deposits of various origin and experienced different time of freezing in nature, showed in the whole a high stability of cell structure to such processes independently on various periods of freezing in sediments and relation to growth temperature. Both in water and soil suspensions permafrost bacteria revealed a high survival capacity without any additional cryoprotectors. All bacterial strains that survived after freezing and thawing revealed halotolerancy in liquid nutrient media with increased concentrations of NaCl (8-20%) that can testify on high stability of those microbes to osmotic stress and possible increased production of intracellular osmoprotectant compatible solutes. The latter can protect bacterial cells against freezing injury in permafrost.

Vera Soina
Lomonosovskii prospect, 14-446
Moscow State University
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RUSSIA
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E-mail: lena@bio.soils.msu.su