Department of Biology, Queen's University, Kingston, ON, Canada.
FEMS Microbiol Ecol. 2012 Nov;82(2):405-15. doi: 10.1111/j.1574-6941.2012.01404.x. Epub 2012 Jun 13.
Osmotic stress can accompany increases in solute concentrations because of freezing or high-salt environments. Consequently, microorganisms from environments with a high-osmotic potential may exhibit cross-tolerance to freeze stress. To test this hypothesis, enrichments derived from the sediment and water of temperate lakes with a range of salt concentrations were subjected to multiple freeze-thaw cycles. Surviving isolates were identified and metagenomes were sampled prior to and following selection. Enrichments from alkali lakes were typically the most freeze-thaw resistant with only 100-fold losses in cell viability, and those from freshwater lakes were most susceptible, with cell numbers reduced at least 100,000-fold. Metagenomic analysis suggested that selection reduced assemblage diversity more in freshwater samples than in those from saline lakes. Survivors included known psychro-, halo- and alkali-tolerant bacteria. Characterization of freeze-thaw-resistant isolates from brine and alkali lakes showed that few isolates had ice-associating activities such as antifreeze or ice nucleation properties. However, all brine- and alkali-derived isolates had high intracellular levels of osmolytes and/or appeared more likely to form biofilms. Conversely, these phenotypes were infrequent amongst the freshwater-derived isolates. These observations are consistent with microbial cross-tolerance between osmotic and freeze-thaw stresses.
渗透胁迫会伴随着溶质浓度的增加而出现，例如在冷冻或高盐环境中。因此，来自高渗透压环境的微生物可能对冷冻胁迫表现出交叉耐受。为了验证这一假设，从具有不同盐浓度的温带湖泊的沉积物和水中进行了富集，并对其进行了多次冻融循环。对存活的分离物进行了鉴定，并在选择前后对宏基因组进行了采样。碱湖的富集物通常具有最强的抗冻融能力，细胞活力仅损失 100 倍，而淡水湖的富集物最易受影响，细胞数量减少至少 100,000 倍。宏基因组分析表明，选择使淡水样本中的群落多样性减少的程度比盐度湖泊中的更大。存活下来的包括已知的嗜冷菌、嗜盐菌和耐碱菌。对来自盐水和碱湖的抗冻融分离物的特性分析表明，很少有分离物具有冰结合活性，如抗冻蛋白或冰核活性。然而，所有来自盐水和碱湖的分离物都具有高细胞内渗透压调节剂水平，或者更有可能形成生物膜。相反，这些表型在来自淡水的分离物中很少见。这些观察结果与渗透胁迫和冻融胁迫之间的微生物交叉耐受一致。
