Does anatoxin-a influence the physiology of Microcystis aeruginosa and Acutodesmus acuminatus under different light and nitrogen conditions?

Due to changing global climatic conditions, a lot of attention has been given to cyanobacteria and their bioactive secondary metabolites. These conditions are expected to increase the frequency of cyanobacterial blooms, and consequently, the concentrations of cyanotoxins in aquatic ecosystems. Unfortunately, there are very few studies that address the effects of cyanotoxins on the physiology of phytoplankton species under different environmental conditions. In the present study, we investigated the effect of the cyanotoxin anatoxin-a (ATX-A) on Microcystis aeruginosa (cyanobacteria) and Acutodesmus acuminatus (chlorophyta) under varying light and nitrogen conditions. Low light (LL) and nitrogen limitation (LN) resulted in significant cell density reduction of the two species, while the effect of ATX-A on M. aeruginosa was not significant. However, under normal (NN) and high nitrogen (HN) concentrations, exposure to ATX-A resulted in significantly (p < 0.05) lower cell density of A. acuminatus. Pigment content of M. aeruginosa significantly (p < 0.05) declined in the presence of ATX-A, regardless of the light condition. Under each light condition, exposure to ATX-A caused a reduction in total microcystin (MC) content of M. aeruginosa. The detected MC levels varied as a function of nitrogen and ATX-A concentrations. The production of reactive oxygen species (H2O2) and antioxidant enzyme activities of both species were significantly altered by ATX-A under different light and nitrogen conditions. Our results revealed that under different light and nitrogen conditions, the response of M. aeruginosa and A. acuminatus to ATX-A was variable, which demonstrated the need for different endpoints of environmental factors during ecotoxicological investigations.