Arab J Sci Eng DOI 10.1007/s13369-015-1808-5 RESEARCH ARTICLE - BIOLOGICAL SCIENCES Biochemical Biomarkers in the Halophilic Nanophytoplankton: Dunaliella salina Isolated from the Saline of Sfax (Tunisia) Taheni Belghith 1 · Khaled Athmouni 1 · Jannet Elloumi 1 · Wassim Guermazi 1 · Thorsten Stoeck 2 · Habib Ayadi 1 Received: 2 February 2015 / Accepted: 23 July 2015 © King Fahd University of Petroleum & Minerals 2015 Abstract The purpose of the present work was to study the potential biotechnological use of Dunaliella species isolated from the solar saltern of Sfax (Tunisia). D. salina was grown in artificial seawater (3.4 M NaCl) under a constant temper- ature (25 ˚C) and light (265 μmol photons m −2 s −1 ). The maximal cellular density was about 4.66 × 10 6 cells/ml, and the growth rate ranged between 0.13 and 0.16 doublings/day. Chlorophyll a reached 52.32 ± 0.12 mg/l in the exponential phase. Protein and carbohydrates content reached maximum values in the lag phase (52.4 ± 0.2 and 5.7 ± 0.34 mg/l, respectively). The maximal values of total lipids content were obtained at the decline phase (92 ± 0.87 mg/l). In addition, during this study, the analyses of the fatty acids profile have shown the presence of essential fatty acids that accumulate in D. salina during the stress phase. Keywords D. salina · Biochemical · Light intensity · Fatty acids · Metabolism 1 Introduction Microalgae have ecological and commercial importance as the base of the food chain, as producers of oxygen, and as a natural source of valuable compounds such as fatty acids, proteins, carbohydrates, and carotenoids [1, 2]. B Khaled Athmouni Khaled_athmouni@hotmail.fr 1 Unité de recherche UR 11 ES 72/Biodiversité et Ecosystèmes Aquatiques, Département des Sciences de la Vie, Faculté des Sciences de Sfax, Université de Sfax, Route soukra Km 3,5, B.P. 1171, 3000 Sfax, Tunisia 2 Erwin-Schroedinger-Str. 14, 67663 Kaiserslautern, Germany Unicellular green algae of the genus Dunaliella (Chloro- phyta) are ovoid, lack a rigid cell wall, contain one large cup-shaped chloroplast, and are motile with two equally long flagellae [3–5]. D. salina [6] is probably the most halotoler- ant eukaryotic species known, showing a remarkable degree of adaptation to a variety of salt concentrations from as low as 0.2 % to salt saturation (about 35 %); it is the only eukaryotic photosynthetic organism that has been detected in significant numbers in concentrated saline lakes [7]. Two constitutive processes seem to be responsible for salinity tolerance: glycerol accumulation and the active elim- ination of Na + ions [8]. Also, the crystal structure of the D. salina carbonic anhydrase revealed features that allow the enzyme to retain conformational stability and solubility from low to high salt concentrations [9, 10]. The hypersaline microalga Dunaliella salina is one of the main strains of microalgae currently cultivated in open ponds, in particular for its ability to produce a variety of secondary metabolites such as β-carotene [11–13]. This molecule is used as food additive for its antioxidant and vitamin [14–18] and is added to numerous pharmaceuticals, cosmetic, and body-care products as a non-harmful colorant to improve the attractiveness of the product [15]. This mobile unicellular green microalga can also accumulate lipids and can thus pro- vide an interesting alternative to fossil fuels [11, 19, 20]. D. salina synthesizes a variety of fatty acids that are responsi- ble for the β-carotene accumulation [21]. It appeared that high-light-induced carotenoid overproduction was associ- ated with oil globule formation and a decrease in the degree of fatty acid unsaturation. Furthermore, β-carotene accumu- lation was found to correlate with the production of specific fatty acid species, namely C16:0 and C18:1, rather than with total fatty acid content [22]. Protein synthesis is enhanced by the environmental conditions such as high salinity that 123