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Objective: Microalgal pharmaceutical biotechnology is mainly dependent on the biomass yield and also the final concentration of the obtained lipids. β-carotene is one of the most precious nutraceuticals, of both preventive and therapeutics importance in pharmacy and medicine. Dunaliella salina is known as famous β-carotene producer which could accumulate the β-carotene up to 10% of its dry cell weights. The amount of different macro and micronutrients in D. salina culture medium defines its productivity and β-carotene content. Methods: In this study, the effects of sulfur, iron and manganese deprivation, on cell growth and β-carotene biosynthesis in a naturally isolated strain of D. salina was examined. Besides, the fatty acid profile of the naturally isolated strain was also investigated. Results: Sulfur, iron and manganese deprivation caused a noticeable decrease in the cell growth of D. salina. On the other hand, in nutrient depleted media, the maximum β-carotene concentration was significantly improved (14.616 mg L-1 in sulfur starvation, 14.994 mg L-1 in iron starvation and 10.119 mg L-1 in manganese starvation media) compared with initial values (6.753 mg L-1) in basic culture medium. The obtained fatty acids from the studied microalgal strain found to be some important saturated, monounsaturated and polyunsaturated fatty acids. Conclusion: Owing to its significant growth rate, β-carotene contents and fatty acid profile; the naturally isolated microalgal strain could be exploited as a potential producer strain. Besides, the nutrient limitation strategy could be effectively employed to improve the β-carotene production procedure in D. salina. This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

Essential roles of microalgae during the tertiary treatment of municipal wastewater have been proven. In order to avoid wash out of the biomass and also modify the quality of the treated wastewater; some techniques such as cell immobilization have been developed. To do so, in this study four samples from two species of microalgae (Chlorella vulgaris and Chlamydomonas sp.) were determined and confirmed by taxonomic identification. The samples were immobilized in calcium alginate beads. Within 10 days the amounts of nitrate (No3(-)-N) and orthophosphate (Po4(3-)-P) were measured to calculate the removal efficacy for each individual sample. Based on the standard methods, the amount of nitrate and orthophosphate were determined every 3 days within 10 days. The results indicate that immobilized microalgae are able to remove the nutrients and reduce the amount of nitrate and orthophosphate, significantly. Furthermore, the C. vulgaris (YG02) was the best species in this experience with 72% and 99% of reduction in the amount of nitrate and orthophosphate, respectively.

In the present study, the effects of hypo-osmotic and hyper-osmotic shock on β-carotene and glycerol production by a native strain of Dunaliella salina isolated from Maharlu Salt Lake, Fars province, Iran, were investigated. The amount of β-carotene and glycerol at 1 h, 2 h, 8 h and 24 h after initiating hypo-osmotic (1 M NaCl) and hyper-osmotic shocks (3 M NaCl); and at normal condition (2 M NaCl) were measured. At hyperosmotic medium, β-carotene concentration reached to maximum amount after 2 h and remained constant up to 24 h. Even so, increasing of glycerol concentration was initiated after 2 h and reached the highest value at 24 h after salinity stress induction. At hypo-osmotic shock, β-carotene and glycerol concentrations were decreased. There are lots of lakes and salt marshes in Iran, which can be suitable environments for growing D. salina. So it seems that the isolated D. salina is potentially useful for planting in small locations to promote the commercial production of β-carotene and glycerol.

Background: Carotenoids are known as lipophilic secondary metabolites with important biological activities, which are mostly used in the food and pharmaceutical industry. They contribute to the colours of many fruits and flowers. Studies on the biosynthetic pathways of isoprenoids and carotenoids are still scarce, especially in microalgae, and are limited to specific groups Dunaliella spp. In the Chlorophyta taxon of algae, the 2-C-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate (DOXP/MEP) is the synthesis pathway of sterols and carotenoids. Objectives: In this study, we used 12 Psy gene sequences in Dunaliella sp., also Scenedesmus acutus, and Diospyros kaki to investigate a genome-wide search. The results are useful for better identification of carotenoids metabolisms and increasing the production rate of beta-carotene in pharmaceutical, food, and industrial processes. Methods: Phytoene synthase (Psy) from Dunaliella spp. was selected as the first regulatory point in the carotenoids pathway that catalysis the formation of geranylgeranyl pyrophosphate in isoprenoid biosynthesis. Structural, evolutionary, and physics-chemical characteristics were investigated using various bioinformatics tools and computer techniques. Moreover, some recently published patents were also regarded. Results: The maximum length of the conserved motif was 5167 bp for Dunaliella. sp. (DQ463306.1), and the smallest length of the conserved motif was 416 bp belong to D. salina (JQ762451.1). The average molecular weight of species was 41820.53 Da. The theoretical pI of species varied from 4.87 to 9.65, indicating vernation in the acidic nature. Two strains of D. bardawil (U91900.1 and EU328287.1) showed just a long-distance relationship with all other Dunaliella strains. Whilst, D. parva displayed the furthest vicinity with all the studied strains. Conclusion: Our study highlighted the Psy regulatory mechanism as a key factor in the carotenoids pathway to facilitate genetic and metabolic engineering studies. The obtained three-dimensional arrangement of the amino acids revealed the regional structures and folding of the diverse segments of helices, sheets, turns. This information is a key point to unveil the protein's operation mechanism. Besides, we confirmed the suitability of bioinformatic approaches for analysing the gene structures and identifying the new Psy genes in unstudied microalgal strains.