Inactivation of Heterosigma akashiwo in Marine Water by UV-Activated Periodate: Efficacy and Mechanism

The combination of ultraviolet (UV) and periodate (PI) is a promising advanced oxidation process. We investigated the inactivation of a typical harmful algae species,Heterosigma akashiwoby UV/PI treatment and explored the inactivation mechanism at the cellular and molecular levels. The inactivation efficacy ofH. akashiwoby UV/PI and UV treatment alone was 9.21-ln and 1.23-ln within 37.5 min, respectively. Hydroxyl radicals (•OH) and singlet oxygen (1O2) contributed toH. akashiwoinactivation in the UV/PI system. Obvious destruction of the cell structure observed by transmission electron microscopy and the increases in extracellular DNA levels indicated membrane damage by the reactive species. The activity changes in the antioxidant enzymes and the decreases in ATP contents ofH. akashiwoafter UV/PI treatment were both more severe than that after UV treatment. The results indicated that the antioxidant defense system and the mitochondria ofH. akashiwocells were disrupted. The photosynthesis was also affected as both of the chlorophyll-a content and the maximum dark-adapted photochemical efficiency (Fv/Fm) ofH. akashiwodecreased obviously. The transcriptomics analysis proved that UV/PI treatment caused abnormal energy metabolism and cell function. Moreover, the down regulation of gene expression enriched in the phagocytic pathway indicated that the cell was severely damaged and inactivated under oxidative stress.