Examination of the Mechanism of Phenanthrenequinone Toxicity To <i>Vibrio Fischeri</i>: Evidence for a Reactive Oxygen Species-Mediated Toxicity Mechanism

Abstract

Phenanthrenequinone (PHQ) is a photoproduct of phenanthrene, one of the most prevalent polycyclic aromatic hydrocarbons in the environment. Phenanthrenequinone is a compound of substantial interest, because its toxicity can be much greater than its parent chemical to aquatic organisms. The toxicity mechanisms of PHQ to the luminescent marine bacterium Vibrio fischeri were examined in the present study. Phenanthrenequinone can redox cycle in bacterial cells and transfer electrons to O2, enhancing the production of superoxide (O*2-), hydrogen peroxide (H2O2), and other reactive oxygen species (ROS). Exposure of cells to PHQ increased activity of superoxide dismutase (SOD), which detoxifies the ROS superoxide. Concentrations of PHQ that induced the production of H2O2 and other ROS, as well as the elevated levels of Fe-SOD, were correlated with its toxicity as measured by luminescence. Furthermore, toxicity of PHQ to V. fischeri was lowered under the anaerobic conditions, suggesting that the absence of oxygen, which would limit the production of ROS, alleviated toxicity of PHQ. Thus, a ROS-mediated toxicity mechanism of PHQ is highly implicated by in the present study.