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

Abstract

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.

Moderate Temperature Fluctuations Rapidly Reduce the Viability of Ralstonia solanacearum Race 3, Biovar 2, in Infected Geranium, Tomato, and Potato Plants

“…The reason for this reduced survival may be that when R. solanacearum cells thaw inside plant tissue where nutrients are available, the bacteria undergo a respiratory burst that increases their vulnerability to damage inflicted by a subsequent freeze. A freeze-thaw cycle is known to induce a respiratory surge in soilborne bacteria, likely stimulated by nutrients released from lysing dead cells (36,38,51). This creates a period of prosperity for the remaining microbes (38), but this temporary bounty may actually be detrimental to longterm survival.…”

Effects of freeze–thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat

“…Freeze-thaw events affect the activity and population dynamics of microorganisms in sediments and soils because strong fluctuations in temperature can damage or destroy microbial cells and disrupt cell aggregates (for example, Schimel and Clein, 1996;Eriksson et al, 2001;Sharma et al, 2006;Mountfort et al, 2003;Schimel and Mikan, 2005;Walker et al, 2006;Yergeau and Kowalchuk, 2008;Männistö et al, 2009). This phenomenon has been studied in soils, in which freezing elevates the salinity while lowering water and nutrient availability (Eriksson et al, 2001;Sharma et al, 2006;Yergeau and Kowalchuk, 2008).…”

Petroleum Hydrocarbon Biodegradation under Seasonal Freeze−Thaw Soil Temperature Regimes in Contaminated Soils from a Sub-Arctic Site

“…Microbial activity at subzero temperatures contributed to biodegradation of the F2 hydrocarbons but not the F3 hydrocarbons. The microbial activity was maintained likely due to the slow rate of soil freezing that limits intercellular ice crystallization and cell damage (11,24). The range of subzero temperatures, for which unbound liquid water can be present, increases with the amount of hydrocarbon contamination and clay content at a given freezing or thawing rate (25,26).…”