Comparative Assessment of Stress Responses of the Microalgae Prorocentrum cordatum (Ostenfeld) Dodge and Dunaliella salina (Teod.) to the Presence of Copper Nanoparticles

-Comparative assessment of stress responses of two microalgal species differing in their cell structure and habitats, Prorocentrum cordatum and Dunaliella salina, to the presence of copper oxide nanoparticles (NP) in the medium was carried out. The nanoparticles were found to have a similar effect on both species. Their toxic effect resulted in progressing production of reactive oxygen species in the algal cells, while their specific growth rates decreased, probably due to Cu2+ release from the oxide or to penetration of some nanoparticles into the cells. NP mechanical impact resulted in their aggregation at the cell surface and deformation of the cell envelopes. The presence in the toxicant in the medium caused a reliable increase in cell volume, plasmalemma perforation, and predominance of deformed cells of irregular shape in the cultures. Two species exhibited different resistance to CuO NP. The sublethal and lethal concentrations for P. cordatum were 400 and 520 mu g/L, respectively, compared to 3000 and 3750 mu g/L for D. salina. The possible causes for resistance of D. salina to CuO NP are discussed. D. salina is able to produce ligands (phytochelatins and metallothionenis) in high concentrations, which may be released into the medium and bind the Cu2+ ions. Moreover, the habitats of D. salina are extreme, which may promote its stress tolerance, probably a genetically determined feature and a part of their overall resistance to other contaminants. High resistance of D. salina to CuO NP may also be due to its ability to secrete extracellular polymers under stress conditions; they may form a protective layer preventing the interaction between the microalgae and NP. Application of P. cordatum for biomonitoring of NP-contaminated seawater environments is proposed. D. salina may be promising for water bioremediation.