The response of Microcystis aeruginosa strain MGK to a single or two consecutive H₂O₂ applications

Various approaches have been proposed to control/eliminate toxic Microcystis sp. blooms including H₂O₂ treatments. Earlier studies showed that pre-exposure of various algae to oxidative stress induced massive cell death when cultures were exposed to an additional H₂O₂ treatment. We examined the vulnerability of exponential and stationary-phase Microcystis sp. strain MGK cultures to single and double H₂O₂ applications. Stationary cultures show a much higher ability to decompose H₂O₂ than younger cultures. Nevertheless, they are more sensitive to an additional H₂O₂ dose given 1–6 h after the first one. Transcript analyses following H₂O₂ application showed a fast rise in glutathione peroxidase abundance (227-fold within an hour) followed by a steep decline thereafter. Other genes potentially engaged in oxidative stress were far less affected. Metabolic-related genes were downregulated after H₂O₂ treatments. Among those examined, the transcript level of prk (encoding phosphoribulose kinase) was the slowest to recover in agreement with the decline in photosynthetic rate revealed by fluorescence measurements. Our findings shed light on the response of Microcystis MGK to oxidative stress suggesting that two consecutive H₂O₂ applications of low concentrations are far more effective in controlling Microcystis sp. population than a single dose of a higher concentration.