High sensitivity of cyanobacterium Microcystis aeruginosa to copper and the prediction of copper toxicity

Abstract

Microcystis aeruginosa is a dominant cyanobacterium commonly found in Chinese freshwater ecosystems during phytoplankton blooms, and copper sulfate is one of the most frequently used algicides for controlling the nuisance blooms. In this study, we examined the effects of varied water chemistry (dissolved organic matter, pH, and hardness) on copper (Cu) toxicity to M. aeruginosa, as well as the Cu short-term uptake kinetics, using (67)Cu as a radioactive tracer. Elevated dissolved organic matter concentrations resulted in a reduction of Cu toxicity, and increasing pH in the range 6.7 to 8.5 led to an increase of Cu toxicity based on the ambient dissolved Cu concentration. The variation of growth inhibition was much more dependent on the intracellular Cu concentration than on the total ambient Cu or calculated free Cu(2+) concentration; thus, the biotic ligand model could be used to explain the Cu toxicity to M. aeruginosa under different water chemistry conditions. We demonstrated that M. aeruginosa were extremely sensitive to Cu toxicity compared with other freshwater phytoplankton species based on the intracellular Cu concentration. The median inhibition concentration of intracellular Cu was as low as 3.3 to 13.1 × 10(-18) mol Cu/cell for all treatments. The Cu short-term uptake kinetics in M. aeruginosa could be explained by the free-ion activity model. The uptake rate, however, could not explain the discrepancy in Cu sensitivity between M. aeruginosa and other phytoplankton species. Other mechanisms might explain the extreme sensitivity of M. aeruginosa to Cu toxicity.