Effects of high light and temperature on Microcystis aeruginosa cell growth and β-cyclocitral emission

Cyanobacteria always massively grow and even occur blooms in summer, with releasing amount of beta-cyclocitral. To uncover the effects of summer high irradiance and temperature on cyanobacterial growth and beta-cyclocitral emission, the cell growth, reactive oxygen species (ROS) levels, photosynthetic pigment content, chlorophyll fluorescence and beta-cyclocitral emission were investigated in Microcystis aeruginosa under high light and temperature. Compared to the control under 50 mu mol m(-2).s(-1), the cell growth was promoted under 100 mu mol m(-2).s(-1), but inhibited under 500 and 1000 mu mol m(-2).s(-1). The inhibition was also detected under high temperature at 30 and 35 degrees C in contrast to the control at 25 degrees C. Under high light and high temperature, M. aeruginosa increased ROS levels and reduced photosynthetic pigment content and photosystem II (PSII) efficiency, which resulted in the inhibition on cell growth. With increasing the light intensity and temperature, O-1(2) levels gradually increased, while beta-carotene content gradually decreased by quenching O-1(2), with increasing beta-cyclocitral emission. In summer, high irradiance and temperature not benefited the growth of cyanobacteria, but the emission of beta-cyclocitral derived from beta-carotene quenching O-1(2) may offset the disadvantages by poisoning other algae.