According to previous studies, Microcystis aeruginosa, a picocyanobacteria, is more sensitive to copper than the other phytoplanktonic species such as Chlorella vulgaris a chlorophycea. An experimental study was carried out to determine the cell wall characteristics of both species. The cell surface of M. aeruginosa presented a lower hydrophobic character and a more negative surface charge over a larger pH range than for C. vulgaris, according to hydrophobicity and zeta potentials measurements. By combining infrared spectroscopy data and potentiometric titrations, the total concentration of functional groups determined for M. aeruginosa (1.60 x 10(-3) mol/g), as well as the number of carboxyl groups, was higher than for the C. vulgaris ones (0.22 x 10(-3) mol/g). The differences in surface properties, as shown by chemical, physicochemical and spectroscopic measurements would justify the differences in sensitivities to copper ions up-take between the two specimens. (C) 2009 Elsevier Inc. All rights reserved.