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.

Potential use of flow cytometry in toxicity studies with microalgae.

Cytotoxic effects of aquatic pollutants on microalgae are very heterogeneous, and they are influenced by environmental conditions and the test species. Stress produced by copper or paraquat addition to the culture medium of two microalgae was analysed by flow cytometry. Parameters assayed were: cell volume, chlorophyll a fluorescence and cell viability. The variety of results obtained in the present study reveals that flow cytometry is a useful tool in the toxicity tests with microalgae, both marine and freshwater species, and for different kind of pollutants.

A comparison of the relative sensitivity of structural and functional cellular responses in the alga chlamydomonas eugametos exposed to the herbicide paraquat.

The effect of the herbicide paraquat on the freshwater microalga Chlamydomonas eugametos was studied in function of different parameters such as growth, elemental composition, total lipids, and photosynthetic pigments content and others assayed by flow cytometry (cell viability, cell volume, and granularity). The study reveals that paraquat concentrations above 0.15 microM are toxic for the microalga C. eugametos, inducing an inhibition of all the physiological parameters analyzed and strong structural changes. However, lower concentrations cause alterations in certain cellular components that are especially sensitive to the toxic action of the herbicide; so total lipids and photosynthetic pigments content are affected by concentrations such low as 0.037 microM. Taking into account these results, these parameters are better indicators of the cellular state than data on biomass or growth rate.