Simulating the Impact of the Natural Radiation Background on Bacterial Systems: Implications for Very Low Radiation Biological Experiments.

Nathanael Lampe,Pierre Marin,David Sarramia,Sébastien Incerti,Jeremy M C Brown,David G Biron,Hervé Seznec,Lydia Maigne,Vincent Breton,Ganesh Chandra Jagetia

doi:10.1371/journal.pone.0166364

Abstract

At very low radiation dose rates, the effects of energy depositions in cells by ionizing radiation is best understood stochastically, as ionizing particles deposit energy along tracks separated by distances often much larger than the size of cells. We present a thorough analysis of the stochastic impact of the natural radiative background on cells, focusing our attention on E. coli grown as part of a long term evolution experiment in both underground and surface laboratories. The chance per day that a particle track interacts with a cell in the surface laboratory was found to be 6 × 10−5 day−1, 100 times less than the expected daily mutation rate for E. coli under our experimental conditions. In order for the chance cells are hit to approach the mutation rate, a gamma background dose rate of 20 μGy hr−1 is predicted to be required.

Highlights

When considering the impact of ionizing radiation on cellular systems from the environment, the absorbed radiation dose is considered by experimentalists
Given the impact of radiation on any system depends on its geometry, we initially present an overview of our experiment, as this influences the conditions under which cells experience the natural radiation environment
We have presented a method for better understanding the impact of low radiation doses on a population of individual cells

Summary

Introduction

When considering the impact of ionizing radiation on cellular systems from the environment, the absorbed radiation dose is considered by experimentalists. Absorbed dose measures a continuous energy deposition per unit mass, when in reality energy is deposited by ionizing particles along tracks For low doses, these tracks do not always cross a significant proportion of cells in the populations studied in a biologically relevant time period [4]. These tracks do not always cross a significant proportion of cells in the populations studied in a biologically relevant time period [4] The magnitude of this effect can be quantified using particle transport simulations to replicate biological experiments and their radiation environments. We discussed the relative contributions of different background sources to biological experiments and presented measured dosages pertinent to these experiments in both above and below ground environments [40] These sources are the terrestrial gamma doi:10.1371/journal.pone.0166364.g002. The LSM’s position underground shelters it from the majority of cosmic rays: here the only significant sources of radiation are the terrestrial gamma background and the background from the nutritive medium

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Conclusion