Investigation of Indirect Radiation Effects in the Model Archaeon Halobacterium sp. NRC-1

P.C. Retka1; J.R. Smith2; and L.C. DeVeaux3 (1Idaho State University - Dept. of Physics/Health Physics Program; 2University of Maryland - Dept. of Biotechnology, Center of Marine Biotechnology; 3Idaho State University - Dept. of Biology/Idaho Accelerator Center)

Radiation affects biological systems by directly interacting with cells and, as described more recently, by eliciting responses in cells that have not received any radiation. These non-targeted, or indirect effects, are of two types. One type of indirect effect is the bystander effect, which is defined as radiation-induced changes in cells that have not received any dose. However, these cells have been in the proximity of cells that have received dose. A second type of indirect effect is delayed genomic instability, where the progeny of cells that have received radiation display genetic effects, long after the dose has been delivered. We are investigating both of these indirect radiation effects in a model organism, the archaebacterium Halobacterium sp. NRC-1 using 18-20 MeV electrons from a pulsed electron LINAC. The genome of this organism contains 91 insertion sequences. Transposition of any of these sequences into the genes for gas vacuole production provides a visual phenotypic assay for genomic instability. We have previously measured a dose-dependent increase in transposition. Reverse transposition, in which the insertion sequence is precisely removed, also increases with dose. We are using both of these events as endpoints for measuring bystander effects, by immediately exposing unirradiated cultures of Halobacterium to cultures that have received either a low dose, or a dose sufficient to cause detectable genomic radiation effects in the targeted culture. We are also using these events, as well as colony size variation, as indicators of genomic instability in the progeny of cells hundreds of generations after irradiation. Student Paper

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