Effects of H 2 O 2 on growth, metabolic activity and membrane integrity in three strains of Microcystis aeruginosa

The application of hydrogen peroxide (H 2 O 2 ) as a management tool to control Microcystis blooms has become increasingly popular due to its short lifetime and targeted action. H 2 O 2 increases intracellular reactive oxygen species resulting in oxidative stress and subsequently cell death. H 2 O 2 is naturally produced in freshwater bodies as a result of photocatalytic reactions between dissolved organic carbon and sunlight. Previously, some studies have suggested that this environmental source of H 2 O 2 selectively targets for toxigenic cyanobacteria strains in the genus Microcystis . Also, past studies only focused on the morphological and biochemical changes of H 2 O 2 -induced cell death in Microcystis with little information available on the effects of different H 2 O 2 concentrations on growth, esterase activity and membrane integrity. Therefore, this study investigated the effects of non-lethal (40–4000 nM) concentrations on percentage cell death; with a focus on sub-lethal (50 μM) and lethal (275 μM; 500 μM) doses of H 2 O 2 on growth, cells showing esterase activity and membrane integrity. The non-lethal dose experiment was part of a preliminary study. Results showed a dose- and time-dependent relationship in all three Microcystis strains post H 2 O 2 treatment. H 2 O 2 resulted in a significant increase in intracellular reactive oxygen species, decreased chlorophyll a content, decreased growth rate and esterase activity. Interestingly, at sub-lethal (50 μM H 2 O 2 treatment), percentage of dead cells in microcystin-producing strains was significantly higher ( p < 0.05) than that in non-microcystin-producing strains at 72 h. These findings further cement our understanding of the influence of H 2 O 2 on different strains of Microcystis and its impact on membrane integrity and metabolic physiology: important to future toxic bloom control programmes.