Different responses of the marine diatom Phaeodactylum tricornutum to copper toxicity

Different responses of the marine diatom Phaeodactylum tricornutum (Bohlin) to toxic copper concentrations were investigated. Besides the classical variables applied to toxicity studies in microalgae, such as growth or chlorophyll a content, other variables analyzed by flow cytometry were used. Toxic effects due to copper concentration were observed. Cell density reached in the stationary phase was reduced to 50% in cultures with 20 mg Cu/l, with respect to control cultures without copper. Cell light scatter properties (related to cell volume and intracellular granularity) and chlorophyll a fluorescence of microalgal cells were determined by flow cytometry analysis at the beginning of growth, 1 h after copper exposure, and when cultures reached the stationary phase (72 h). After 1 h of exposure to metal, no differences were observed, but when cultures reached the stationary phase, a gradual increase in the variables analyzed by flow cytometry was observed as the copper concentration increased. The increase in chlorophyll a fluorescence detected by flow cytometry was not correlated with an increase in the cell content of this photopigment, thus indicating an inhibitory effect of copper on photosystem II.