Effects of freeze-thaw stress on bacterial populations in soil microcosms

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Abstract
To test the effect of freezing on soil biota, isolated from the shortgrass prairie of northeastern Colorado, a series of experiments were performed using gnotobiotic soil microcosms.Pseudomonas paucimobilis was used to examine the effects of freezing on bacteria of different growth stages. Secondly, the effect of multiple freeze-thaw cycles was tested on an assemblage of bacterial species. Lastly, the effect of freezing on predator-prey interactions was studied usingP. paucimobilis and an amoebal predator,Acanthamoeba polyphaga. A temperature of −9°C was not detrimental toP. paucimobilis at any growth stage. A single severe freeze-thaw cycle (−27°C to 23°C) resulted in 40–60% mortality ofP. paucimobilis and the mixed bacteria, although additional freezing events did not reduce the populations further. Multiple freeze-thaw cycles (−9°C to 23°C) gave 40–60% mortality ofP. paucimobilis and the mixed bacteria. Predator-prey population cycles were possibly desynchronized by freeze-thaw events.