Enhanced suppression effects on Microcystis aeruginosa by combining hydrogen peroxide and intermittent UVC irradiation: The importance of triggering advanced oxidation process within cells.

In order to strengthen the inhibitory effect of UVC/HO on Microcystis aeruginosa growth, this study designed a novel strategy for inducing an advanced oxidation process in algal cells by splitting UVC irradiation into two rounds. The first irradiation of UVC upon adding HO facilitated the delivery of HO into the cell cytoplasm, which induced an intracellular advanced oxidation process after the second irradiation of UVC. The intermittent treatment of UVC/HO could further attack the Ca-Mn and Fe-S clusters in the photosynthetic electron transport chain. In contrast, conventional simultaneous treatment of UVC/HO only attacked the interaction subunits between PSII cores and the phycobilisome. The block of the photosynthetic electron transport chain, shedding of the Ca-Mn cluster, and damage of the Fe-S cluster gave rise to massive intracellular HO, O, and HO•. Consequently, ROS acted as a mediator and led to caspase-3(-like) activation and the subsequent initiation of apoptosis-like cell death. The remarkable functional mechanisms make the intermittent treatment of UVC/HO an ideal method for the practical application of suppressing HABs (target-selective, long-lasting, cost-minimized, and eco-friendly).