Nitrate and iron nutrition effects on some nitrate assimilation enzymes and metabolites in Spirulina platensis

Effects of different sodium nitrate and iron concentrations on the production of some metabolites and pigments and the activities of some nitrate assimilation enzymes [nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT)] were investigated in the growth medium of Spirulina platensis (Gamont) Geitler. For this purpose, S. platensis was cultivated on Zarrouk’s medium containing different sodium nitrate concentrations (10–180 mM). A 100 mM sodium nitrate concentration stimulated growth of this organism as well as the production of pigments and other metabolites and enzyme activities. In the presence of 100 mM sodium nitrate, different concentrations of iron (10–100 μM) were tried in the growth medium of S. platensis. The highest enzyme activities were determined in the presence of 100 mM sodium nitrate and 50 μM iron. The highest NR, NiR, GS, and GOGAT activities obtained were 126.92 ± 9.2 U mL^–1, 841.16 ± 61.4 U mL^–1, 0.1301 ± 0.02 U mL^–1, and 46.18 ± 1.8 U mL^–1, respectively. These high enzymatic activities may stimulate high amino acid production. Higher enzyme activity may result in higher nutritional value in S. platensis, which has wide usage in biotechnology, industry, and biochemistry.