Copper toxicity on the marine microalga Phaeodactylum tricornutum: effects on photosynthesis and related parameters

Essential heavy metals, as copper, can be toxic for microalgae at high concentrations. Copper affected growth and other parameters closely related to photosynthesis of the marine diatom Phaeodactylum tricornutum. A copper concentration of 0.10 mg l provoked about 50% growth reduction and 1 mg linhibited the growth. Copper also interfered with photosynthesis and ATP production. A copper concentration of 0.5 mg l reduced in a 50% the photosynthetic rate. Therefore, growth is more affected by copper than photosynthesis. Results of chlorophyll a fluorescence obtained by flow cytometry showed that copper's inhibitory effect on PS II activity is located on its oxidizing side. The lower copper concentration assayed provoked a significant decrease in the cellular pool of ATP. Pigment analysis by HPLC showed that copper affected the pigment pattern of P. tricornutum. Important changes were observed for chlorophyll a and its allomer: chlorophyll a proportion decreased while its allomer increased with the copper concentration, being maximum at 1 mg Cu l. The study of the intracellular pH by flow cytometry revealed that P. tricornutumcells exposed to 0.5 and 1 mg Cu l showed an intracellular pH higher than control cultures cells, explaining the high proportion of the chlorophyll a allomer in these cells.