Effects of Exogenous Reactive Oxygen Species Scavengers on the Survival of Escherichia coli B23 During Exposure to UV-A radiation

Solar disinfection of water is a well-studied technique to cheaply and easily sterilize microbecontaminated water through a combination of heat and UV-induced reactive oxygen species (ROS). Understanding the role of exogenous environmental compounds on the efficacy of the protocol as well as the optimization of an accurate bacterial enumeration strategy is integral to maximize the efficacy of this technique. A time course assay of E. coli B23 viability during UV- A irradiation was conducted, and the effects of L-histidine, formate, catalase and superoxide dismutase as scavengers of ROS were tested. Stepwise declines in bacterial cell numbers were observed in all UV-irradiated samples, and minimal effects on the decline were observed with the addition of formate or L-histidine. Catalase and superoxide dismutase appeared to decrease bacterial survival. Inability to effectively access internal cellular photosensitizers might have contributed to the inconclusive results with regards to formate and L-histidine. Changes in pH due to addition of excess enzyme may have played a role in the increase in bacterial cell death with catalase treatment. Exogenous compounds seem to play a role in the bactericidal efficacy of the SODIS protocol, however the results included here are only preliminary observations. Further studies of confounding variables such as pH, concentration, and temperature are required to fully characterize the impact of ROS quenching.