Multi-Biomarker Response of Cyanobacteria Synechocystis salina and Microcystis aeruginosa to Diclofenac

The cyanobacterial response to pharmaceuticals is rarely tested compared to green algae. Pharmaceuticals can influence not only the growth rate of cyanobacteria culture, but can also cause changes at the cellular level. The effect of diclofenac (DCF) as one of the for cyanobacteria has been rarely tested, and DCF has never been applied with cellular biomarkers. The aim of this work was to test the response of two unicellular cyanobacteria (Synechocystis salina and Microcystis aeruginosa) toward DCF (100 mg L−1) under photoautotrophic growth conditions. Such endpoints were analyzed as cells number, DCF uptake, the change in concentrations of photosynthetic pigments, the production of toxins, and chlorophyll a in vivo fluorescence. It was noted that during a 96 h exposure, cell proliferation was not impacted. Nevertheless, a biochemical response was observed. The increased production of microcystin was noted for M. aeruginosa. Due to the negligible absorption of DCF into cells, it is possible that the biochemical changes are induced by an external signal. The application of non-standard biomarkers demonstrates the effect of DCF on microorganism metabolism without a corresponding effect on biomass. The high resistance of cyanobacteria to DCF and the stimulating effect of DCF on the secretion of toxins raise concerns for environment biodiversity. The presented research has shown that reference ecotoxicological tests do not provide us with sufficient information regarding the impacts of pollutants on cyanobacteria. Despite having no effects on the growth of cyanobacteria, DCF had stimulated the cyanobacterial for production of microcystins. Additionally, it has been noticed that cyanobacteria are more resistant to DCF than other phytoplankton species, and thus, they have an advantage in a polluted environment. Although the DCF concentration tested was not at environmental levels, testing the acute toxicity of DCF on cyanobacteria allows for an understanding of the mechanisms of its action in cyanobacteria.