Biological effects of hydroxyl radical inactivation for typical red tide algae Alexandrium tamarense

Abstract

Dinoflagellates are responsible for harmful algal blooms (HABs) worldwide and cause serious ecological security crises and economic losses to the aquaculture industry. In this study, hydroxyl radicals (•OH) were generated by the synergistic effect of strong ionization discharge and hydrodynamic cavitation and were injected into cells to inactivate Alexandrium tamarense within 9 s at a total reactive oxidant (TRO) concentration of 1.0 mg/L. The concentration and time (CT) value of •OH inactivating A. tamarense was 0.153 mg•min/L, which is 1/100 that of ClO2 inactivation. Scanning electron microscopy results demonstrated that the integrity of the algal cells remained without any leakage of intracellular organic matter post •OH inactivation. Furthermore, the chromosomes in the nucleus unwound and broke into fragments under a transmission electron microscope, indicating that the DNA was damaged. In comparison, ClO2 contributed to the severe destruction of cell membranes and walls, resulting in massive intracellular organic matter (IOM) leakage. Based on the single cell gel electrophoresis results, DNA comet length increased 329 % post •OH inactivation, demonstrating that •OH induced DNA fragmentation. Additionally, based on the transcriptomic analysis of A. tamarense, •OH induced a DNA repair response, indicating that DNA strand breakage occurred. In summary, DNA strand breakage and fragmentation were the major reasons for •OH rapidly inactivating A. tamarense with cell integrity retained, which provided critical advancements in controlling HAB safely and efficiently. This method avoids the risk of A. tamarense lysis and IOM release, while guaranteeing marine water security.