Some biological responses of the diatom Nitzschia closterium (W. Smith) to copper and zinc

Some biological responses of the marine diatom Nitzschia closterium to copper and zinc were studied. The species was isolated from the Gulf of Suez and grown in liquid culture with enriched filtered seawater over a maximum period of 10 days. The results indicated that low concentrations of copper (1 and 5 μg.l-1) and zinc (10, 20 and 50 μg.l-1) stimulated the growth, photosynthetic pigments (chlorophyll-a,c and carotenoids), total soluble proteins as well as 02-evolution in photosynthesis and dark respiration (02uptake) of the diatom as compared with the control culture. Whereas, higher concentrations of 50, 100, 200 and 300 μg.l-1 copper and 100, 200, 300, 400 and 600 μg.l-1 zinc inhibited the above metabolic processes of the organism (taking into consideration that the culture treated with 10 μg.l-1 zinc produced the same O2-uptake as in the control culture). Statistically, there exists reverse correlation between the different concentrations of copper and zinc and the metabolic processes of Nitzschia closterium as proved with linear regression equations