IntroductionCyanobacteria are photosynthetic bacteria that use sunlight as an energy source, water as an electron donor, and carbon dioxide as a carbon source to produce food. They use oxygen to support life and usually live in fresh or marine water. They produce organic material and thus they are known as primary producers (Ozturk Urek and Tarhan, 2011;Tian et al., 2014). The cyanobacterium Spirulina platensis is a filamentous, nitrate-utilizing, nonnitrogenfixing, photosynthetic organism that is rich in pigments such as chlorophyll a, carotenoids, and phycobiliproteins. These properties make it very important in nutritional, industrial, and environmental biotechnology (Tarko et al., 2012). It is a healthy food and also has defensive properties against viral diseases and anemia. It is used as a colorant because of its rich pigment content (Henrikson, 2010;Singh et al., 2014). Antioxidant properties and the high vitamin, protein, carbohydrate, and mineral values of S. platensis inhibit tumor growth and malnutrition. S. platensis is rich in protein content and contains 60%-70% protein by dry weight (Jha et al., 2007), including 9 essential amino acids that are considered high-quality protein (Belay, 2008). Nitrogen is an essential element due to nitrogen assimilation or incorporation of the most important functional and structural macromolecules in organisms, such as amino acids. Nitrogen is the most important element due to its approximately 10% contribution to cyanobacterium cells (Perez-Garcia et al., 2011), with 15% of this rate composed of incorporated proteins and nucleic acids (Inokuchi et al., 2002).Minerals are the other vital members involved in the growth and enzymatic activities of S. platensis (Tarko et al., 2012). The growth and metabolic activity of cyanobacteria may be limited by a variety of these minerals. They affect the growth and metabolic activity of Spirulina (Ozturk Urek and Tarhan, 2011). One of the most important elements for the growth of Spirulina is iron (Fe). It is a limiting factor for pigment production (chlorophyll a). Investigations into the relationship between chlorophyll a biosynthesis and iron show that iron deficiency causes chlorosis. It decreases chlorophyll a and heme production and represses porphyrin biosynthesis (Belkhodja et al., 1998; Briat et al., 2007; Reinbothe et al., 2010). Additionally, Fe is a significantly important element for nitrogen assimilatory enzymes. The structures of the enzymes consist of Fe as cofactor. Cubic clusters of Fe and
