Combined effects of microcystin and nitrite on the growth, lipid peroxidation, and antioxidant responses of the freshwater rotifer Brachionus calyciflorus.

Toxicants released during the degradation of cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite (NO2 -N), affect the growth of aquatic organisms. The freshwater rotifer Brachionus calyciflorus was exposed to solutions with different combined concentrations of MC-LR (0, 10, 50, 100, and 200μgL-1 ) and NO2 -N (0, 2, 4, 6, and 8mgL-1 ) to assess the combined effects of MC-LR and NO2 -N on life cycle parameters and oxidative stress. Single solutions of MC-LR 200μgL-1 and NO2 -N 8mgL-1 were toxic to rotifers. MC-LR combined with NO2 -N decreased population growth rate (r), survival, and reproduction, but increased reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH) contents (p<0.01). Superoxide dismutase (SOD) and catalase (CAT) activities and mRNA expression levels of MnSOD, CuZnSOD, and CAT significantly decreased under high concentrations of MC-LR or NO2 -N (p<0.05). ROS levels had negative correlations with antioxidant enzyme activities and expression levels of antioxidant genes (p<0.01). MC-LR and NO2 -N had interactive effects on r, reproduction, ROS levels, MDA content, SOD activity, and expression levels of MnSOD and CAT (p<0.05). By contrast, these effects were antagonistic on survival, CAT activity, GSH content, and expression level of CuZnSOD (p>0.05). Results showed that cyanobacterial metabolites act synergistically and antagonistically to cause toxicity to B. calyciflorus. ROS-mediated toxicity was considered the mechanism by which MC-LR and NO2 -N induce damage.