title: Stress induction in the bacteria Shewanella oneidensis and Deinococcus radiodurans in response to below-background ionizing radiation.
abstract: OBJECTIVE
  The 'Linear no-threshold' (LNT) model predicts that any amount of radiation increases the risk of organisms to accumulate negative effects. Several studies at below background radiation levels (4.5-11.4 nGy h(-1)) show decreased growth rates and an increased susceptibility to oxidative stress. The purpose of our study is to obtain molecular evidence of a stress response in Shewanella oneidensis and Deinococcus radiodurans grown at a gamma dose rate of 0.16 nGy h(-1), about 400 times less than normal background radiation.
  
  
  METHODS
  Bacteria cultures were grown at a dose rate of 0.16 or 71.3 nGy h(-1) gamma irradiation. Total RNA was extracted from samples at early-exponential and stationary phases for the rt-PCR relative quantification (radiation-deprived treatment/background radiation control) of the stress-related genes katB (catalase), recA (recombinase), oxyR (oxidative stress transcriptional regulator), lexA (SOS regulon transcriptional repressor), dnaK (heat shock protein 70) and SOA0154 (putative heavy metal efflux pump).
  
  
  RESULTS
  Deprivation of normal levels of radiation caused a reduction in growth of both bacterial species, accompanied by the upregulation of katB, recA, SOA0154 genes in S. oneidensis and the upregulation of dnaK in D. radiodurans. When cells were returned to background radiation levels, growth rates recovered and the stress response dissipated.
  
  
  CONCLUSIONS
  Our results indicate that below-background levels of radiation inhibited growth and elicited a stress response in two species of bacteria, contrary to the LNT model prediction.
authors.affiliation: a Department of Biology , New Mexico State University , Las Cruces , NM , USA.
authors.forename: Hugo
authors.initials: H
authors.lastname: Castillo
authors.affiliation: b Department of Agriculture , Food, and Nutritional Science, University of Alberta , Edmonton , Alberta, Canada.
authors.forename: Donald
authors.initials: D
authors.lastname: Schoderbek
authors.affiliation: c School of Medicine, University of North Carolina , Chapel Hill NC.
authors.forename: Santosh
authors.initials: S
authors.lastname: Dulal
authors.affiliation: a Department of Biology , New Mexico State University , Las Cruces , NM , USA.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Escobar
authors.affiliation: d Department of Energy-Carlsbad Field Office , Carlsbad , NM , USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Wood
authors.affiliation: d Department of Energy-Carlsbad Field Office , Carlsbad , NM , USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Nelson
authors.affiliation: a Department of Biology , New Mexico State University , Las Cruces , NM , USA.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Smith
mesh_terms: D001417:Background Radiation / Q000009:adverse effects; D034301:Deinococcus / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects; D005798:Genes, Bacterial / Q000528:radiation effects; D008954:Models, Biological; D018384:Oxidative Stress / Q000528:radiation effects; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics; D020592:Shewanella / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D013312:Stress, Physiological / Q000528:radiation effects*
chemical_list: D012329:RNA, Bacterial
keywords: Below-background radiation; relative gene expression; stress response