Intracellular Copper Accumulation Enhances the Growth of Kineococcus radiotolerans during Chronic Irradiation

Environmental Sciences and Biotechnology, Savannah River National Laboratory, Aiken, SC, USA; Electron Microscopy Center, University of South Carolina, Columbia, SC, USA

^* To whom correspondence should be addressed. Email: Christopher.bagwell{at}srnl.doe.gov.

	Abstract

The actinobacteria Kineococcus radiotolerans is highly resistant to ionizing radiation, desiccation, and oxidative stress; though the underlying biochemical mechanisms are unknown. The purpose of this study was to explore a possible linkage between the uptake of transition metals and extreme resistance to ionizing radiation and oxidative stress. The effects of 6 different divalent cationic metals on growth were examined in the absence of ionizing radiation. None of the metals tested were stimulatory, though cobalt was inhibitory to growth. In contrast, copper supplementation dramatically increased colony formation during chronic irradiation. K. radiotolerans exhibited specific uptake and intracellular accumulation of copper compared to only a weak response to both iron and manganese supplementation. Copper accumulation sensitized cells to hydrogen peroxide. Acute irradiation induced DNA damage was similar between the copper-loaded culture as the age-synchronized no copper control culture, though low molecular weight DNA was more persistent during post-irradiation recovery in the Cu-loaded culture. Still, the estimated times for genome restoration differed by only 2 hrs between treatments. While we cannot discount the possibility that copper fulfills an unexpectedly important biochemical role in a low-level radioactive environment; K. radiotolerans has a high capacity for intracellular copper sequestration, and presumably efficiently coordinated oxidative stress defenses and detoxification systems, which confers cross-protection from the damaging affects ionizing radiation.