Interactive effects of microcystin and ammonia on the reproductive performance and phenotypic traits of the rotifer Brachionus calyciflorus.

Elevated microcystin-LR (MC-LR) and ammonia (NH3-N) concentrations co-occur during the degradation of Microcystis blooms, and are toxic to aquatic organisms. The freshwater rotifer, Brachionus calyciflorus, was exposed to mixtures of MC-LR (0, 10, 30, and 100µgL-1) and NH3-N (0, 270, and 540µgL-1) to assess the combined effects of the two toxicants on reproductive performance and phenotype traits. Single solutions of MC-LR (100µgL-1) and NH3-N (540µgL-1) had negative effects on rotifer reproductive timing and fecundity. Pre- and post-reproductive periods fluctuated with MC-LR and NH3-N concentrations, while reproductive period and total offspring per female were reduced in mixtures of MC-LR and NH3-N (p < 0.05). Grazing rate of rotifers decreased with grazing time and concentrations of the two toxicants (p < 0.001). MC-LR in combination with NH3-N had negative effects on swimming speed and body length but positively stimulated posterolateral spine development (p < 0.001). MC-LR and NH3-N had synergetic interactive effects on pre-reproductive period, reproductive period, total offspring per female, grazing rate, swimming speed, and body length (p < 0.05). In contrast, these effects were antagonistic on post-reproductive period and posterolateral spine length (p > 0.05). These results indicate that MC-LR and NH3-N act synergistically and antagonistically in causing toxicity to B. calyciflorus regarding reproductive performance and the formation of defensive phenotypes.

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.