Effects of metals (Ag, Cd, Cu) on the biochemical composition and compartmentalization of these metals in two microalgae Skeletonema costatum and Tetraselmis suecica

Effects at sublethal silver, cadmium, and copper concentrations on growth a nd biochemical composition of two marine microalgae Tetraselmis suecica and Skeletonema costatum revealed that growth is by far the most sensitive fac tor, whereas cellular content of polysaccharides, proteins, lipids, and pig ments are not significantly affected. This suggests that the first target o f these metals is cell division and processes related to it. Heavy metal co ncentrations in algal cells were lower in S. costatum than in T. suecica, a nd the study of metal partitioning showed that for both algal species, Cd w as firmly bound onto the cell wall or had entered the cell, whereas 40% of the initially adsorbed Cu was easily released after treatment by the chelat ing agent. However, in both algal species, Cd and Cu were predominantly pre sent in the insoluble fraction, and in the cytosol, thermoresistant metal-c helating polypeptids are involved. For this study, the major metal detoxifi cation process in algae exposed to sublethal concentrations is therefore th eir binding to insoluble components. The strong stability of the later sugg ests less bioavailability and maybe a limited transfer of these metals to h igher trophic levels.