Effect of nitrite on growth and microcystins production of Microcystis aeruginosa PCC7806

As a common pollutant, nitrite concentrations can approach 15 mg NO (2) (-) -N L(-1) in some aquatic systems. Microcystis aeruginosa blooms are common and widespread in eutrophic freshwater bodies. In this study, M. aeruginosa was exposed to nitrite concentrations ranging from 0 to 15 mg NO (2) (-) -N L(-1), and the responses of M. aeruginosa were investigated. The specific growth rates, maximum cell densities, light-saturated photosynthetic rates (P(m) (chla) ), dark respiration rates (R(d) (chla) ), and apparent photosynthetic efficiencies (alpha(chla) ) showed a significant decline with nitrite concentrations increasing. Electrical conductivity and malondialdehyde contents investigation revealed cell membrane damage and apparent leakage of intracellular contents under high nitrite level conditions due to oxidative stress enhancement. Intracellular microcystin (MC)-LR content reached the highest value at 10 mg NO (2) (-) -N L(-1); however, extracellular MC-LR contents showed a continuous increase until 15 mg NO (2) (-) -N L(-1) owing to the increasing leakage of intracellular contents. These results elucidated that the high-level nitrite inhibited M. aeruginosa growth by rising oxidative stress, damaging cell membrane, and reducing photosynthesis. However, the moderate increase in nitrite concentrations promoted toxin production and release of toxin.