The ecological risks of hydrogen peroxide as a cyanocide: its effect on the community structure of bacterioplankton

Microcystis blooms are an environmental and ecological concern that has received a serious attention. Hydrogen peroxide (H2O2) is an environment-friendly cyanocide that is commonly used to control Microcystis blooms. While the ecological safety of H2O2 has been previously studied, its influence on bacterioplankton has not been investigated to date. In this study, we used mesocosm experiments to determine the influence of H2O2 on the dynamic changes of the community structure of bacterioplankton. By using deep-sequencing and metagenomics strategy we determined the community structures of phytoplankton and bacterioplankton assemblages that were dominated by Microcystis at a highly eutrophic Dianchi Lake, China. The results showed that Microcystis was more sensitive to H2O2 than other eukaryotic algae. More interestingly, application of H2O2 changed the community structure of bacterioplankton, evidenced by the emergence of Firmicutes as the dominant species in place of Bacteroidetes and Proteobacteria. The H2O2 treatment resulted in the community of bacterioplankton that was primarily dominated by Exiguobacterium and Planomicrobium. Our results show that the abundance changed and the bacterioplankton diversity did not recover even after the concentration of H2O2 reached to the background level. Thus, the response of bacterioplankton must be considered when assessing the ecological risks of using H2O2 to control Microcystis blooms, because bacterioplankton is the key player that forms the basis of food web of aquatic environment.