P25: Oxidative stress response of Halobacterium salinarum to ionizing radiation and chemical oxidants

Hypersaline environments pose unique challenges to organisms that inhabit them, including UV radiation and desiccation. These conditions introduce oxidative stress to the cells from unchecked production of reactive oxygen species (ROS).  As a consequence, organisms have developed robust defense systems for combating ROS. The halophilic archaeon Halobacterium salinarum is highly resistant to desiccation, UV, and ionizing radiation (IR). Exposure to IR results in cellular oxidative damage via radiolysis of water and production of ROS. This study aimed to understand the cellular damage and stress response of H. salinarum exposed to chemical oxidants and IR. 

H. salinarum cells exposed to IR showed a high level of oxidative damage to DNA and proteins. In contrast, exposure to hydrogen peroxide and superoxide - to the same level of survival - produced significantly less oxidative damage, indicating that cell death from chemical oxidants might be the result of interference with major metabolic pathways.  We found that ROS scavenging enzymes essential for survival to hydrogen peroxide and superoxide were not necessary for H. salinarum survival to IR.  Enzyme-free cellular extracts from H. salinarum showed high level of protection for protein activity against IR. Biochemical analysis of the enzyme-free extracts revealed essential roles in ROS scavenging for specific nucleosides, MnPO₄ complexes, the accumulation of free amino acids and peptides, and high intracellular halides.  This work contributed novel findings on the critical role played by non-enzymatic systems in IR resistance in H. salinarum and underlines the diversity of mechanisms that exists in response to environmental stresses.