Hugo Castillo1, Donald Schoderbek2, Santosh Dulal3, Gabriela Escobar1, Jeffrey Wood4, Roger Nelson4, Geoffrey Smith1. 1. a Department of Biology , New Mexico State University , Las Cruces , NM , USA. 2. b Department of Agriculture , Food, and Nutritional Science, University of Alberta , Edmonton , Alberta, Canada. 3. c School of Medicine, University of North Carolina , Chapel Hill NC. 4. d Department of Energy-Carlsbad Field Office , Carlsbad , NM , USA.
Abstract
PURPOSE: 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. MATERIALS AND 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.
PURPOSE: 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. MATERIALS AND 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: Nathanael Lampe; David G Biron; Jeremy M C Brown; Sébastien Incerti; Pierre Marin; Lydia Maigne; David Sarramia; Hervé Seznec; Vincent Breton Journal: PLoS One Date: 2016-11-16 Impact factor: 3.240
Authors: Nathanael Lampe; Vincent Breton; David Sarramia; Télesphore Sime-Ngando; David G Biron Journal: Evol Appl Date: 2017-06-07 Impact factor: 5.183