A Major Role for Nonenzymatic Antioxidant Processes in the Radioresistance of Halobacterium salinarum

Author:

Robinson Courtney K.1,Webb Kim1,Kaur Amardeep2,Jaruga Pawel3,Dizdaroglu Miral3,Baliga Nitin S.2,Place Allen4,DiRuggiero Jocelyne1

Affiliation:

1. Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218

2. Institute for Systems Biology, Seattle, Washington 98103

3. Biochemical Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20999

4. Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21202

Abstract

ABSTRACT Oxidative stress occurs when the generation of reactive oxygen species (ROS) exceeds the capacity of the cell's endogenous systems to neutralize them. Our analyses of the cellular damage and oxidative stress responses of the archaeon Halobacterium salinarum exposed to ionizing radiation (IR) revealed a critical role played by nonenzymatic antioxidant processes in the resistance of H. salinarum to IR. ROS-scavenging enzymes were essential for resistance to chemical oxidants, yet those enzymes were not necessary for H. salinarum 's resistance to IR. We found that protein-free cell extracts from H. salinarum provided a high level of protection for protein activity against IR in vitro but did not protect DNA significantly. Compared with cell extracts of radiation-sensitive bacteria, H. salinarum extracts were enriched in manganese, amino acids, and peptides, supporting an essential role in ROS scavenging for those small molecules in vivo . With regard to chemical oxidants, we showed that the damage caused by gamma irradiation was mechanistically different than that produced by hydrogen peroxide or by the superoxide-generating redox-cycling drug paraquat. The data presented support the idea that IR resistance is most likely achieved by a “metabolic route,” with a combination of tightly coordinated physiological processes.

Publisher

American Society for Microbiology

Subject

Molecular Biology,Microbiology

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