Single and combined toxicity of copper and cadmium on Microcystis aeruginosa: effects on growth, oxidative stress and gene expression

Copper (Cu) and cadmium (Cd) are commonly found in polluted water bodies due to intensive anthropogenic activities, but their combined toxicity on Microcystis aeruginosa remains unknown. The present study conducted a 96-h cultivation experiment to investigate the toxicity effects of Cu and Cd, both individually and in mixture, on the growth, oxidative response and gene expression of Microcystis aeruginosa . Results showed that Cd alone had no negative impact on M. aeruginosa growth; whereas growth was significantly inhibited by Cu alone and by the mixture. High concentrations of Cu (200 µg L − 1 ) and Cd (50 µg L − 1 ), as well as their mixture, induced oxidative stress in M. aeruginosa . The ftsH gene, prx gene, fabZ gene and recA gene were all up-regulated by high concentrations of Cu (200 µg L − 1 ), Cd (50 µg L − 1 ) and their mixtures (100 + 25 and 200 + 50 µg L − 1 ), which however, decreased the expression of the psbA gene. The combined toxicity assessment suggested that synergistic interaction occurred in treatments with low Cu and Cd concentrations (100 + 25 µg L − 1 ). Our results suggest that the toxicity effects of Cu and Cd are exacerbated when they co-exist in the natural environment at relatively low concentrations.