title: Microarray transcriptional profiling of Arctic Mesorhizobium strain N33 at low temperature provides insights into cold adaption strategies.
abstract: BACKGROUND
  Arctic Mesorhizobium strain N33 was isolated from nodules of the legume Oxytropis arctobia in Canada's eastern Arctic. This symbiotic bacterium can grow at temperatures ranging from 0 to 30 °C, fix nitrogen at 10 °C, and is one of the best known cold-adapted rhizobia. Despite the economic potential of this bacterium for northern regions, the key molecular mechanisms of its cold adaptation remain poorly understood.
  
  
  RESULTS
  Using a microarray printed with 5760 Arctic Mesorhizobium genomic clones, we performed a partial transcriptome analysis of strain N33 grown under eight different temperature conditions, including both sustained and transient cold treatments, compared with cells grown at room temperature. Cells treated under constant (4 and 10 °C) low temperatures expressed a prominent number of induced genes distinct from cells treated to short-term cold-exposure (<60 min), but exhibited an intermediate expression profile when exposed to a prolonged cold exposure (240 min). The most prominent up-regulated genes encode proteins involved in metabolite transport, transcription regulation, protein turnover, oxidoreductase activity, cryoprotection (mannitol, polyamines), fatty acid metabolism, and membrane fluidity. The main categories of genes affected in N33 during cold treatment are sugar transport and protein translocation, lipid biosynthesis, and NADH oxidoreductase (quinone) activity. Some genes were significantly down-regulated and classified in secretion, energy production and conversion, amino acid transport, cell motility, cell envelope and outer membrane biogenesis functions. This might suggest growth cessation or reduction, which is an important strategy to adjust cellular function and save energy under cold stress conditions.
  
  
  CONCLUSIONS
  Our analysis revealed a complex series of changes associated with cold exposure adaptation and constant growth at low temperatures. Moreover, it highlighted some of the strategies and different physiological states that Mesorhizobium strain N33 has developed to adapt to the cold environment of the Canadian high Arctic and has revealed candidate genes potentially involved in cold adaptation.
authors.affiliation: Graduate Programs in Agri-Food Microbiology, Faculty of Agriculture and Food Sciences, Laval University, Quebec City, Quebec, G1V 0A6, Canada. Ghobakhloufa@gmail.com.
authors.forename: Abdollah-Fardin
authors.initials: AF
authors.lastname: Ghobakhlou
authors.affiliation: Eastern Cereal & Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, K1A 0C6, Canada. Anne.Johnston@agr.gc.ca.
authors.forename: Anne
authors.initials: A
authors.lastname: Johnston
authors.affiliation: Eastern Cereal & Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, K1A 0C6, Canada. Linda.Harris@agr.gc.ca.
authors.forename: Linda
authors.initials: L
authors.lastname: Harris
authors.affiliation: Department of Soils and Agri-Food Engineering, Laval University, Quebec City, Quebec, G1V 0A6, Canada. Hani.antoun.1@ulaval.ca.
authors.forename: Hani
authors.initials: H
authors.lastname: Antoun
authors.affiliation: Soils and Crops Research Development Center, Agriculture and Agri-Food Canada, Quebec City, Quebec, G1V 2 J3, Canada. Laberge.r@videotron.ca.
authors.forename: Serge
authors.initials: S
authors.lastname: Laberge
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000254:growth & development; D001692:Biological Transport / Q000235:genetics; D050260:Carbohydrate Metabolism / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D016000:Cluster Analysis; D003080:Cold Temperature; D004260:DNA Repair / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D004734:Energy Metabolism / Q000235:genetics; D020869:Gene Expression Profiling; D023281:Genomics; D050356:Lipid Metabolism / Q000235:genetics; D059128:Mesorhizobium / Q000166:cytology / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D018832:Molecular Chaperones / Q000378:metabolism; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D009711:Nucleotides / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D017382:Reactive Oxygen Species / Q000378:metabolism; D011995:Recombination, Genetic / Q000235:genetics; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D013312:Stress, Physiological / Q000235:genetics; D013559:Symbiosis / Q000235:genetics; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018832:Molecular Chaperones; D009711:Nucleotides; D017382:Reactive Oxygen Species; D014157:Transcription Factors