Physiological responses to ferrate (VI) stress in Microcystis aeruginosa

Potassium ferrate (VI) has been considered to be an environmentally friendly oxidant. In this paper, a research on the physiological and biochemical changes of the ferrate (VI)´s acting on Microcystis aeruginosa FACHB-905, a common kind in algal bloom, has been performed. Under the action of ferrate (VI), chlorophyll-a content, the photosynthetic oxygen evolution rate, maximum electron transport rate (ETR_m) and maximum photochemical efficiency (Fv/Fm) of Microcystis aeruginosa were significantly decreased, while MC-LR, an extracellular toxin of Microcystis aeruginosa increased. Malonaldehyde (MDA) is oxidatively stressed by low concentration of ferrate (VI). With the increasing concentration of ferrate (VI), MDA content increases, and the activity of SOD and CAT also shows a significant rise. After the treatment of low concentration ferrate (VI), GST activity decreased rapidly, while with the further increasing of ferrate (VI), GST activity increased gradually. This shows that ferrate (VI) produces oxidative stress on Microcystis aeruginosa. The mechanism is that ferrate (VI) inhibits the activity of microcystin photosynthetic PS II system, which leads to the damage to photosynthesis. The accumulation of excessive intracellular free radicals can further lead to the lipid peroxidation of membrane, increasing the membrane permeability, finally causes the death of Microcystis aeruginosa.