Studies on DNA fragmentation and cell integrity of rapidly hydroxyl radical inactivated Microcystis aeruginosa

Abstract

Microcystis aeruginosa (M. aeruginosa) blooms occur frequently in freshwater lakes and reservoirs, posing a great threaten to drinking water safety. When using conventional oxidants remedy toxic algae, there is an unavoidable shortage leading to cell rupture and release of intracellular organic matter (IOM), thus causing more serious hazard to water safety. In this study, with the synergistic effect of strong ionisation discharge and hydrodynamic cavitation, hydroxyl radical (•OH) were generated and injected into cells to inactivate M. aeruginosa within 3 s. •OH-inactivated M. aeruginosa was intact without rupture and exhibited a 39 % increase in dissolved organic carbon (DOC) due to the degradation of the components of the cell wall and extracellular matrix. For comparison, ClO2 inactivated M. aeruginosa after 10 min of exposure, which induced cell rupture and a 113 % increase in DOC due to the release of IOM. Meanwhile, in •OH-inactivated M. aeruginosa, intracellular •OH was increased to 2 times according to the detection by fluorescence probe and the DNA oxidative damage biomarker 8-hydroxy-2′-deoxyguanosine increased to 1.4 times according to the enzyme-linked immunosorbent assay, confirming the direct action of •OH on the DNA. And •OH induced DNA fragmentation in cells of M. aeruginosa was identified by comet assay and TUNEL assay, finding a 4636 % increase in the DNA tail length, and 96.71 % of the cells showed DNA phosphatediester bond cleavage. In summary, the main reason for the rapid •OH-inactivation of M. aeruginosa is DNA fragmentation, which may represent a new method for the safely and efficient control of harmful algal blooms.