Involvement of oxidative stress in UV-induced impairment of bacterial activity and culturability

The role of UV-induced oxidative stress (intracellular reactive oxygen species generation, DNA strand breakage and lipid peroxidation) in the inhibition of bacterial culturability and activity upon irradiation was assessed during experimental exposure of 9 different bacterial isolates to UV-B radiation. Intracellular ROS were quantified using the fluorimetric probe DCFH-DA. DNA strand breaks were determined using the fluorimetric analysis of DNA unwinding (FADU) method, while lipid peroxidation was assessed from the production of malonaldehyde (MDA). Bacterial culturability was assessed by enumeration of colony forming units (CFU) and bacterial activity was assessed by the incorporation of radiolabeled leucine. UV-B exposure resulted in a strong increase in intracellular ROS levels (12.4-42.3%), accompanied by enhanced formation of lipid peroxidation products (22.1-30.7%) in all strains. Bacterial culturability was inhibited by as much as 89.4% while bacterial activity was reduced by up to 99.6%. The results obtained reveal the contribution of oxidative stress in the impairment of bacterial culturability and activity and suggest the involvement of differences in the extent of oxidative damage in the variability of the responses of aquatic bacteria to UV-B radiation.