Effects of submerged macrophyte Ceratophyllum demersum on ROS generation and cell damage in Microcystis aeruginosa

In laboratory bioassay, we investigated the generation of reactive oxygen species (ROS) in cyanobacteria Microcystis aeruginosa induced by allelopathic effects of submerged macrophyte Ceratophyllum demersum in co-culture system and the changes in cell membrane integrity and DNA damage. We found that the growth inhibition of M. aeruginosa significantly increased with the increase in C. demersum biomass (0.5, 1.0, 3.0 and 6.0 g FW/L). The concentrations of total phenolic compounds (TPCs) secreted by C. demersum in co-culture water increased with the increase in C. demersum biomass and co-culture time. Compared with control, the level of ROS increased in a dose-dependent manner with the biomass of C. demersum and the concentration of TPCs in co-culture water from the second day. According to the propidium iodide (PI) staining results, numbers of cells losing the membrane integrity increased with ROS generation in M. aeruginosa co-cultured with 1.0, 3.0 and 6.0 g FW/L C. demersum on the fourth day. The significant DNA fragmentation was observed in M. aeruginosa cells at 6 g FW/L C. demersum group. These results suggested that the overproduction of ROS induced by the submerged macrophyte C. demersum was the major factor, resulting in the loss of cell membrane integrity and DNA fragmentation and finally leading to the death of M. aeruginosa cells.