Effects of arsenic on growth and photosystem II (PSII) activity of Microcystis aeruginosa

Effects of arsenic on growth, pigments content, oxygen evolution and photosystem II (PSII) activity of Microcystis aeruginosa were investigated in the present study. Various concentrations of As(III) did not show significant effects on growth and total carotenoids content within 24h of treatment. After 48h of treatment, 10mgL−1 As(III) significantly inhibited the growth and synthesis of carotenoids of M. aeruginosa, while As(III) at concentrations ranging from 0 to 1mgL−1 showed no significant inhibition. Chlorophyll a synthesis, oxygen evolution and chlorophyll fluorescence were more sensitive to As(III) exposure than carotenoid synthesis and growth. Chlorophyll a content, fast fluorescence rise transients and fluorescence decay kinetics appeared to be affected after the cells were exposed to 1 and 10mgL−1 As(III) for more than 24h. Treatment with 10mgL−1 As(III) for 24h or longer led to flattening of the fluorescence transient and drastic decrease of amplitude of fast phase of QA− reoxidation kinetics. Exposure to As(III) mainly inhibited the quantum yield for primary photochemistry, density of reaction centers and photosynthesis performance index, and increased the dissipated energy. The decrease in amplitude of the fast and middle phases further revealed that once electron transfer from QA− to QB was inhibited by As(III), more QA− was reoxidized via S2(QAQB)− charge recombination. As(III) stress may result in an increased stability of the S2QB− and S2QA− recombination. ► Growth and PSII activity were significantly inhibited by 10mgL−1 As3+. ► As3+ decreased RC density and PIABS but increased dissipated energy. ► Electron transfer from QA− to QB was inhibited under stress of As3+. ► More QA− was reoxidized via S2(QAQB)− charge recombination under stress of As3+.