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 24 h of treatment. After 48 h of treatment, 10 mg L(-1) As(III) significantly inhibited the growth and synthesis of carotenoids of M. aeruginosa, while As(III) at concentrations ranging from 0 to 1 mg L(-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 10 mg L(-1) As(III) for more than 24 h. Treatment with 10 mg L(-1) As(III) for 24 h 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.