title: Architecture of thermal adaptation in an Exiguobacterium sibiricum strain isolated from 3 million year old permafrost: a genome and transcriptome approach.
abstract: BACKGROUND
  Many microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, however not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. We used Exiguobacterium sibiricum strain 255-15, a psychrotrophic bacterium from 3 million year old Siberian permafrost that grows from -5 degrees C to 39 degrees C to study its thermal adaptation.
  
  
  RESULTS
  The E. sibiricum genome has one chromosome and two small plasmids with a total of 3,015 protein-encoding genes (CDS), and a GC content of 47.7%. The genome and transcriptome analysis along with the organism's known physiology was used to better understand its thermal adaptation. A total of 27%, 3.2%, and 5.2% of E. sibiricum CDS spotted on the DNA microarray detected differentially expressed genes in cells grown at -2.5 degrees C, 10 degrees C, and 39 degrees C, respectively, when compared to cells grown at 28 degrees C. The hypothetical and unknown genes represented 10.6%, 0.89%, and 2.3% of the CDS differentially expressed when grown at -2.5 degrees C, 10 degrees C, and 39 degrees C versus 28 degrees C, respectively.
  
  
  CONCLUSIONS
  The results show that E. sibiricum is constitutively adapted to cold temperatures stressful to mesophiles since little differential gene expression was observed between 4 degrees C and 28 degrees C, but at the extremities of its Arrhenius growth profile, namely -2.5 degrees C and 39 degrees C, several physiological and metabolic adaptations associated with stress responses were observed.
authors.affiliation: Michigan State University, NASA Astrobiology Institute and Center for Microbial Ecology, East Lansing, MI 48824, USA. rodri257@msu.edu
authors.forename: Debora F
authors.initials: DF
authors.lastname: Rodrigues
authors.forename: Natalia
authors.initials: N
authors.lastname: Ivanova
authors.forename: Zhili
authors.initials: Z
authors.lastname: He
authors.forename: Marianne
authors.initials: M
authors.lastname: Huebner
authors.forename: Jizhong
authors.initials: J
authors.lastname: Zhou
authors.forename: James M
authors.initials: JM
authors.lastname: Tiedje
mesh_terms: D000064:Acclimatization / Q000235:genetics* / Q000502:physiology; D000596:Amino Acids / Q000378:metabolism; D050260:Carbohydrate Metabolism; D003080:Cold Temperature; D004261:DNA Replication; D004734:Energy Metabolism; D020869:Gene Expression Profiling; D016680:Genome, Bacterial / Q000235:genetics*; D006093:Gram-Positive Asporogenous Rods / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D009711:Nucleotides / Q000378:metabolism; D012800:Siberia; D014158:Transcription, Genetic
chemical_list: D000596:Amino Acids; D009711:Nucleotides