title: Cross-tolerance between osmotic and freeze-thaw stress in microbial assemblages from temperate lakes.
abstract: 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.
authors.affiliation: Department of Biology, Queen's University, Kingston, ON, Canada.
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Wilson
authors.forename: Corey
authors.initials: C
authors.lastname: Frazer
authors.forename: Brian F
authors.initials: BF
authors.lastname: Cumming
authors.forename: Paulo A S
authors.initials: PA
authors.lastname: Nuin
authors.forename: Virginia K
authors.initials: VK
authors.lastname: Walker
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D018441:Biofilms; D003451:Cryoprotective Agents; D004269:DNA, Bacterial / Q000235:genetics; D005615:Freezing; D007053:Ice; D060106:Lakes / Q000382:microbiology*; D054892:Metagenome; D050296:Microbial Viability; D009995:Osmosis; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D054712:Salinity; D014867:Water / Q000737:chemistry; D014871:Water Microbiology
chemical_list: D003451:Cryoprotective Agents; D004269:DNA, Bacterial; D007053:Ice; D012336:RNA, Ribosomal, 16S; D014867:Water