Sorption isotherm studies of Cd(II) ions using living cells of the marine microalga Tetraselmis suecica (Kylin) Butch.

The present work reports the use of living cells of the marine microalga Tetraselmis suecica for the biosorption of cadmium ions. For a better understanding of the biosorption characteristics, three fractions of removed cadmium (total, bioadsorbed and intracellular) were measured in the cells after 24 and 72 h of exposure to different initial cadmium concentrations (0.6-45 mg L(-1)). Both the Langmuir and Freundlich models were suitable for describing the sorption of cadmium ions by this microalga. The maximum sorption capacity was estimated to be 40.22 mg Cd g(-1) after 72 h using the Langmuir sorption model. In the lower cadmium concentrations, metal removed intracellularly was higher than that removed on the microalgal cell surface. Therefore, the intracellular fraction contributed more to the total removed cadmium than the fraction bioadsorbed to the cellular surface. The results showed that the cadmium removal capacity using living biomass could be much more effective than with non-living biomass due to the intracellular bioaccumulation. According to the microorganism selected and its tolerance to the toxic effect of the metal, the cadmium content in the intracellular fraction can become very significant, just like it happened with Tetraselmis.

Dunaliella salina as marine microalga highly tolerant to but a poor remover of cadmium.

Cadmium tolerance and removal in the marine microalga Dunaliella salina were studied in cultures exposed to different metal concentrations (5-120 mg Cd l(-1)) for 96h. This microalga can be included in the group of microalgal species most tolerant to cadmium due to the high value of EC50 that it possesses (48.9 mg Cd l(-1) at 96 h of culture). The greater percentage of cadmium removed was obtained in cultures exposed to 5 mg Cd l(-1) at 96h, but removing only 11.3% of the added cadmium. In all cultures, the quantity of cadmium removed intracellularly was much lower than the bioadsorbed quantity and it was proportional to the sulfhydryl group levels. Both the Freundlich and Langmuir adsorption models were suitable for describing the short-term biosorption of cadmium by living cells of D. salina.

Comparison of the sensitivity of different toxicity test endpoints in a microalga exposed to the herbicide paraquat.

The use of herbicides constitutes the principal method of weed control but the introduction of these compounds into the aquatic environment can provoke severe consequences for non-target organisms such as microalgae. Toxic effects of these pollutants on microalgae are generally evaluated using phytotoxicity tests based on growth inhibition, a population-based parameter. However, physiological cellular endpoints could allow early detection of cell stress and elucidate underlying toxicity mechanisms. Effects of the herbicide paraquat on the freshwater microalga Chlamydomonas moewusii were studied to evaluate growth rate and cellular parameters such as cellular viability and metabolic activity assayed by flow cytometry and DNA damage assayed by the comet assay. Sensitivity of growth and parameters assayed by flow cytometry were similar, showing a significant effect in cultures exposed to a paraquat concentration of 0.1 microM or higher, although in cultures exposed during 48 h to 0.05 microM, a significant stimulation of cellular fluorescein fluorescence was observed, related to cellular metabolic activity. After only 24 h of herbicide exposure significant DNA damage was observed in microalgal cells exposed to all paraquat concentrations assayed, with a 23.67% of comets in cultures exposed to 0.05 microM, revealing the genotoxicity of this herbicide. Taking into account the results obtained, comet assay provides a sensitive and rapid system for measuring primary DNA damage in Chlamydomonas moewusii, which could be an important aspect of environmental genotoxicity monitoring in surface waters.

Analysis and enhancement of astaxanthin accumulation in Haematococcus pluvialis.

The green microalga Haematococcus pluvialis was cultured with different concentrations of NaNO(3) to determine the effect on cell growth and astaxanthin accumulation. The optimum nitrate concentration to obtain astaxanthin and to avoid the cessation of cell division was 0.15 g/l NaNO(3). The ratio chlorophyll a/total carotenoids proved a good physiological indicator of nitrogen deficiency in the cell. The effect of different carbon sources, malonate and acetate, on astaxanthin accumulation was also studied; up to 13 times more carotenoids per cell were accumulated in cultures with malonate than in cultures without this compound. The pigment analysis was performed by a new low toxicity HPLC method capable of separating chlorophylls a and b, carotenes and xanthophylls in a short-period of time, using low volumes of solvents and with an economical price. With this method even echinenone was separated, which had been unsuccessful by any other method.

Toxic action of copper on the membrane system of a marine diatom measured by flow cytometry.

Flow cytometric measurements were used to investigate the toxic action of copper on some Phaeodactylum tricornutum membrane systems. Throughout the time of metal exposure, the percentage of viable cells decreased as copper concentration increased. The forward scatter signal increased as a result of copper exposure. After 72 h of metal exposure, cultures with 0.5 and 1 mg l-1 of copper showed an important increase in the peroxidase activity in comparison with control cells. Cells cultured with copper presented alterations in the membrane potential, increasing as copper concentration increased, after 96 h of metal exposure. Results obtained in this work showed that copper induced a degenerative process in P. tricornutum cells, closely related with alternations or disorders in membrane systems.

Flow cytometry determination of acute physiological changes in a marine diatom stressed by copper.

Flow cytometry (FCM) was used to determine changes in cellular volume, transmembrane potential, mitochondrial membrane potential and intracellular pH in the marine microalga Phaeodactylum tricornutum immediately (5 to 10 seconds) after the addition of selected concentrations of copper. An acute increase in the forward scatter signal of this diatom was detected after the addition of 10 mg 1-1 of copper. Stress produced by the copper addition resulted in various physiological alterations that can be easily and quickly detected by FCM: (i) the hyperpolarization of the cell membrane, as a result of an immediate increase in the cytoplasmic membrane potential, (ii) the increase of the mitochondrial membrane potential, being maximum at the higher copper concentration assayed, and (iii) the increase in the intracellular pH with the highest copper concentration assayed (10 mg 1-1).

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.