Linda C. DeVeaux1, Shiladitya DasSarma2, Priya A. DasSarma2, Patrick Gygli1, and Surendra Prajapati1. (1) Biological Sciences, Idaho State University, 921 S. 8th, MS 8007, Pocatello, ID 83209, (2) Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 E. Pratt St., Suite 236, Baltimore, MD 21202
Extremely halophilic Archaea are highly resistant to multiple stressors, including both ionizing and non-ionizing radiation, desiccation, and salinity. In order to understand the cellular mechanisms involved in this resistance, we have selected for multiple independent mutants of the model archaeon Halobacterium sp. NRC-1 with increased resistance to high energy electrons. Whole-genome transcriptome analysis revealed one common change: up-regulation of an operon containing one of three homologs to Replication Protein A (RPA), a highly-conserved single-stranded DNA binding protein involved in replication, repair and recombination. Two of the three genes encoded in this operon, rfa3 and rfa8, are homologous to the large and medium subunits, respectively, of eukaryotic RPA. Although transcription of this operon has also been shown to increase after exposure to non-ionizing radiation, these mutants do not have increased survival after exposure to UV. One mutant is considerably more sensitive to UV than the parent strain, indicating presence of a mutation in a UV specific repair mechanism. We have also measured cross-resistance to other stresses, including hydrogen peroxide and antibiotics with varying modes of action, and found no increased resistance among the mutant strains. The ease with which such radiation-resistant varieties were obtained raises important questions about cell responses to extremely high doses of radiation, and has applications to fields as diverse as food sterilization and planetary protection.
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