Role of RecA in the Protection of DNA Damage by UV-A in Escherichia coli

Solar Water Disinfection (SODIS) is a simple, yet effective method for water decontamination by utilizing heat and UV-A from sunlight to kill microbes. However, the mechanism for UV-A mediated cell death is unknown. UV-A has been shown to cause DNA damage by the induction of reactive oxygen species (ROS). This damage might cause cell death in SODIS. Therefore, we investigated whether limiting the repair of DNA damaged by UV-A can increase bacterial susceptibility to UV-A. RecA is a DNA repair regulator protein that is activated upon stresses such as heat and reactive oxygen. In this study, we used Escherichia coli strains with and without RecA to determine survival frequencies after UV-A irradiation. recA cells with functional RecA showed a higher survival frequency compared to RecA mutants after 120 minutes of UV-A exposure, while a smaller difference was observed when cells were cultured without light. These results suggest that the absence of RecA is correlated with an increased vulnerability of cells under UV-A exposure. This difference in sensitivity is most likely due to the inability of mutant bacteria to repair DNA damages. Further studies are required to determine not only the effects of RecA on repairing DNA damage, but also other bactericidal mechanisms exerted by UV-A because the presence of RecA was insufficient to fully protect the treated cells.