Characterization of the Polysaccharides Released by the Toxic Marine Dinoflagellate Alexandrium catenella Under Metal Stress

Abstract

A laboratory study was conducted in order to characterize the polysaccharides exudated by the marine toxic dinoflagellate Alexandrium catenella under metal stress conditions. Cultures were exposed to increasing free metal concentrations of copper ([Cu2+] = 2.51 × 10−9–1.27 × 10−8 mol/l), zinc ([Zn2+] = 2.80 × 10−7–1.00 × 10−6 mol/l), cadmium ([Cd2+] = 2.59 × 10−8–7.80 × 10−8 mol/l) and lead ([Pb2+] = 1.14 × 10−8–4.37 × 10−8 mol/l). The composition in aldoses of the polysaccharides exudated in the culture media was analyzed by gas chromatography. In comparison with the controls, the exudation of polysaccharides was greatly increased under metal stress, to reach its maximal values expressed as specific amounts in total aldoses at the highest levels of metal contamination (copper: 1.1 × 10−3 μg Cell−1 at 7.06 × 10−9 mol/l and 4.7 × 10−3 μg Cell−1 at 1.27 × 10−8 mol/l; lead: 1.15 × 10−3 μg Cell−1 at 2.6 × 10−8 mol/l). Composition in aldoses of the polysaccharides exudated was different according to the metal studied and to the contamination levels. Results showed that glucose represented the major aldose composing the polysaccharides released and being able to take part in metal speciation. The authors conclude that high levels of glucose released by A. catenella in its extracellular medium could take a part in some survival strategies setup by the dinoflagellate to adapt to metal stress.