Growth, physiochemical and antioxidant responses of overwintering benthic cyanobacteria to hydrogen peroxide

The recruitment of overwintering benthic cyanobacteria from the sediment surface is important for the development of cyanobacterial blooms during warm spring seasons. Thus, controlling the growth of cyanobacteria at the benthic stage to inhibit their recruitment is vital to control or delay the formation of summer blooms. In this study, overwintering benthic cyanobacteria were exposed to ascending hydrogen peroxide (H₂O₂) concentrations (0, 1, 5, and 20 mg/L) in a simulated overwintering environment. Photosynthetic pigments, physiochemical features, and antioxidant responses were evaluated to determine the inhibitory effects of H₂O₂ on the growth of benthic cyanobacteria and to identify the potential mechanisms thereof. These H₂O₂-treated cyanobacteria were then collected through filtration and transferred to an optimum environment to evaluate their recovery capacity. The results showed that chlorophyll a and phycocyanin contents, photosynthetic yield, and esterase activity decreased significantly in H₂O₂ treated groups compared to the control. The activities of superoxide dismutase (SOD) and catalase (CAT) in benthic cyanobacteria were inhibited after 72 h exposure to H₂O₂, while the malondialdehyde (MDA) contents were stimulated at the same time. These results indicate that H₂O₂ can inhibit the growth of benthic cyanobacteria, and H₂O₂-induced oxidative damage might be one of the mechanisms involved. The recovery experiment showed that the impairment of benthic cyanobacteria was temporary at a low dose of 1 mg/L H₂O₂, but permanent damage was induced when H₂O₂ concentrations were increased to 5 and 20 mg/L. Overall, our results highlight that H₂O₂ is a potential cyanobacteria inhibitor and can be used to decreasing the biomass of overwintering cyanobacteria, and could further control the intensity of cyanobacteria during the growth seasons.