DNA double-strand breaks induced by reactive oxygen species promote DNA polymerase IV activity inEscherichia coli

Under many conditions the killing of bacterial cells by antibiotics is potentiated by DNA damage induced by reactive oxygen species (ROS) 1–3 . A primary cause of ROS-induced cell death is the accumulation of DNA double-strand breaks (DSBs) 1,4–6 . DNA polymerase IV (pol IV), an error-prone DNA polymerase produced at elevated levels in cells experiencing DNA damage, has been implicated both in ROS-dependent killing and in DSBR 7–15 . Here, we show using single-molecule fluorescence microscopy that ROS-induced DSBs promote pol IV activity in two ways. First, exposure to the antibiotics ciprofloxacin and trimethoprim triggers an SOS-mediated increase in intracellular pol IV concentrations that is strongly dependent on both ROS and DSBR. Second, in cells that constitutively express pol IV, treatment with an ROS scavenger dramatically reduces the number of pol IV foci formed upon exposure to antibiotics, indicating a role for pol IV in the repair of ROS-induced DSBs.