Impact of melatonin on the hydrogen peroxide treatment efficacy in Microcystis aeruginosa: Cell growth, oxidative stress response, and gene transcription

A study was conducted to determine how melatonin (MLT), a growth regulator, affects Microcystis aeruginosa cell behaviour and how MLT exposed cells respond to hydrogen peroxide (H 2 O 2 ) treatment. MLT promotes the growth, chl- a content, Fv/Fm values, and microcystins (MCs) production of M. aeruginosa at low concentrations of 1–2.5 μmol/L but suppresses the growth at high concentrations (5–10 μmol/L). The cellular and genetic responses of MLT pre-treated cells to H 2 O 2 treatment were examined further. Further research found that the cells pre-treated with MLT were susceptible to a range of growth-promoting, inhibiting and lethal effects when exposed to higher levels of H 2 O 2 . A dose-dependent pattern was observed under conditions of 0.05–0.2 mmol/L H 2 O 2 with 0.5–2.5 μmol/L MLT concentrations to different degrees. High doses of H 2 O 2 (0.2 and 0.3 mmol/L) typically lead to cell lysis and release of MCs in 5.0 and 10 μmol/L MLT pre-treated cells. A decrease in SOD/CAT activities and an increase in MDA levels validated the growth reduction. Furthermore, higher cell lysis and release of intracellular MCs were observed when H 2 O 2 was increased for 5–10 μmol/L MLT pre-treated cells. This led to a higher accumulation of extracellular MCs. The results provide insight into how MLT influences H 2 O 2 damage and assist in identifying situations where H 2 O 2 treatment of cyanobacterial blooms is most appropriate.