Abstract
Microcystis blooms have become a ubiquitous phenomenon in freshwater ecosystems, and the size of Microcystis colonies varies widely throughout the year. In the present study, hydrogen peroxide (H2O2) was applied to test the effect of this algaecide on Microcystis colonies of different sizes and to evaluate the colonies’ antioxidant strategy. The results showed that Microcystis populations collapsed under treatment with 5 mg/L H2O2 at colony sizes smaller than 25 μm. A dosage of 20 mg/L H2O2 was necessary to efficiently control Microcystis colonies larger than 25 μm. The enzymatic and non-enzymatic antioxidant systems of different colonies exhibited various strategies to mitigate oxidative stress. In small colonies, superoxide dismutase (SOD) activity was readily stimulated and operated with catalase (CAT) activity to eliminate reactive oxygen species (ROS). In colonies larger than 25 μm, the antioxidant enzyme CAT and antioxidant substance glutathione (GSH) played major roles in mitigating oxidative stress at H2O2 concentrations below 20 mg/L. In addition, application of the algaecide led to the release of intracellular-microcystins (MCs), and oxidatively-driven MCs reached high concentrations when colony size was larger than 100 μm. Algaecide control measures should be implemented before the formation of large colonies to limit the algaecide dosage and MC release.
Highlights
The frequent outbreak of freshwater cyanobacteria blooms has become a ubiquitous phenomenon throughout the world, and outbreaks have been increasing in frequency over the past several decades [1]
The optimal dosage of H2 O2 required to efficiently eliminate Microcystis blooms depends on the colony size when algal biomass is same
Microcystis colonies less than 25 μm collapsed under treatment with 5 mg/L H2 O2
Summary
The frequent outbreak of freshwater cyanobacteria blooms has become a ubiquitous phenomenon throughout the world, and outbreaks have been increasing in frequency over the past several decades [1]. Cyanobacteria have the potential to produce health-affecting toxins and odorous compounds that restrict the usage of lakes and lake water for ecosystem services of societal and economic importance, including the provision of drinking water, irrigation, aquaculture, fish breeding, and recreation. Water blooms can lead to severe water quality problems and negatively affect fisheries as well as civil, industrial and recreational uses of water resources [4]. Microcystis is one of the dominant genus in cyanobacteria blooms [3]. This species produces hepatotoxin microcystins (MCs), which are monocyclic heptapeptides that act as eukaryotic
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