Dunaliella salina (Chlorophyceae), Phormidium versicolor (Cyanophyceae), and Cylindrotheca closterium (Bacillariophyceae) were isolated from three ponds in the solar saltern of Sfax (Tunisia). Growth, pigment contents, and photosynthetic and antioxidant enzyme activities were measured under controlled conditions of three light levels (300, 500, and 1000 µmol photons m−2 s−1) and three NaCl concentrations (40, 80, and 140 g L−1). The highest salinity reduced the growth of D. salina and P. versicolor NCC466 and strongly inhibited that of C. closterium. According to ΦPSII values, the photosynthetic apparatus of P. versicolor was stimulated by increasing salinity, whereas that of D. salina and C. closterium was decreased by irradiance rise. The production of carotenoids in D. salina and P. versicolor was stimulated when salinity and irradiance increased, whereas it decreased in the diatom. Catalase (CAT), Superoxide dismutase (SOD), and Ascorbate peroxidase (APX) activities were only detected when the three species were cultivated under E1000. The antioxidant activity of carotenoids could compensate for the low antioxidant enzyme activity measured in D. salina. Salinity and irradiation levels interact with the physiology of three species that have mechanisms of more or less effective stress resistance, hence different resistance to environmental stresses according to the species. Under these stress-controlled conditions, P. versicolor and C. closterium strains could provide promising sources of extremolyte for several purposes.
With the demand for bioproducts that can provide benefits for biotechnology sectors like pharmaceuticals, nutraceuticals, and cosmeceuticals, the exploration of microalgal products has turned toward extremophiles. This chapter is intended to provide an insight to most important molecules from halotolerant species, the cyanobacteria Phormidium versicolor NCC-466 and Dunaliella sp. CTM20028 isolated from Sfax Solar Saltern (Sfax) and Chott El-Djerid (Tozeur), Tunisia. These microalgae have been cultured in standard medium with a salinity of 80 PSU. The in vitro antioxidant activities demonstrated that extremolyte from Dunaliella and Phormidium as, phycocaynin, lipids, and polyphenol compound presents an important antioxidant potential.
Dunaliella salina (Chlorophyceae), Phormidium versicolor (Cyanophyceae) and Cylindrotheca closterium (Bacillariophyceae) were isolated from three ponds in the solar saltern of Sfax (Tunisia) having an average salinity of 350, 100 and 90 respectively. Growth, pigment contents, photosynthetic and antioxidant enzyme activities were measured under controlled conditions: three light levels (300, 500 and 1000 µmol photons m-2 s-1) and three NaCl concentrations (40, 80 and 140 g L-1). The highest salinity reduced the growth of D. salina and P. versicolor, and strongly inhibited that of C. closterium. These results are in accordance with the species distibution in the salt marshes. Irradiance rise only induced a significant increase of net photosynthesis in C. closterium probably due to the efficient nonphotochemical quenching and antioxidative enzyme activities. According to □PSII values, the photosynthetic apparatus of P. versicolor was stimulated by increasing salinity whereas that of D. salina and C. closterium was decreased by irradiance rise. The production of carotenoids in D. salina and P. versicolor was stimulated when salinity and irradiance increased whereas it decreased in the diatom. Antioxidant activity of carotenoids could compensate the low antioxidant enzyme activity measured in D. salina.
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