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Applied and Environmental Microbiology, March 2006, p. 1784-1792, Vol. 72, No. 3
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.3.1784-1792.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Freeze-Thaw Tolerance and Clues to the Winter Survival of a Soil Community

Virginia K. Walker,^1* Gerald R. Palmer,¹ and Gerrit Voordouw²

Department of Biology, Queens University, Kingston, Ontario, Canada K7L 3N6,¹ Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4²

Received 9 September 2005/ Accepted 14 December 2005

Although efforts have been made to sample microorganisms from polar regions and to investigate a few of the properties that facilitate survival at freezing or subzero temperatures, soil communities that overwinter in areas exposed to alternate freezing and thawing caused by Foehn or Chinook winds have been largely overlooked. We designed and constructed a cryocycler to automatically subject soil cultures to alternating freeze-thaw cycles. After 48 freeze-thaw cycles, control Escherichia coli and Pseudomonas chlororaphis isolates were no longer viable. Mixed cultures derived from soil samples collected from a Chinook zone showed that the population complexity and viability were reduced after 48 cycles. However, when bacteria that were still viable after the freeze-thaw treatments were used to obtain selected cultures, these cultures proved to be >1,000-fold more freeze-thaw tolerant than the original consortium. Single-colony isolates obtained from survivors after an additional 48 freeze-thaw cycles were putatively identified by 16S RNA gene fragment sequencing. Five different genera were recognized, and one of the cultures, Chryseobacterium sp. strain C14, inhibited ice recrystallization, a property characteristic of antifreeze proteins that prevents the growth of large, potentially damaging ice crystals at temperatures close to the melting temperature. This strain was also notable since cell-free medium derived from cultures of it appeared to enhance the multiple freeze-thaw survival of another isolate, Enterococcus sp. strain C8. The results of this study and the development of a cryocycler should allow further investigations into the biochemical and soil community adaptations to the rigors of a Chinook environment.

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* Corresponding author. Mailing address: Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6. Phone: (613) 533-6123. Fax: (613) 533-6617. E-mail: walkervk{at}biology.queensu.ca.

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Applied and Environmental Microbiology, March 2006, p. 1784-1792, Vol. 72, No. 3
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.3.1784-1792.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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