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

The effect of various concentrations of ammonium nitrate (5-60mM), an economical nitrogen source, on the growth, nitrate-ammonium uptake rates, production of some pigments and metabolites, and some nitrogen assimilation enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) in Spirulina platensis (Gamont) Geitler was investigated. Ten millimolars of ammonium nitrate stimulated the growth, production of pigments and the other metabolites, and enzyme activities, whereas 30 and 60mM ammonium nitrate caused inhibition. In the presence of 10mM ammonium nitrate, different concentrations of iron were tried in the growth media of S. platensis. After achieving the best growth, levels of metabolite and pigment production, and enzyme activities in the presence of 10mM ammonium nitrate as a nitrogen source, different iron concentrations (10-100 mu M) were tried in the growth medium of S. platensis. The highest growth, pigment and metabolite levels, and enzyme activities were determined in the medium containing 50 mu M iron and 10mM ammonium nitrate. In this optimum condition, the highest dry biomass level, chlorophyll a, and pyruvate contents were obtained as 55.42 +/- 3.8 mg mL(-1), 93.114 +/- 7.9 mu gg(-1), and 212.5 +/- 18.7 mu gg(-1), respectively. The highest NR, NiR, GS, and GOGAT activities were 67.16 +/- 5.1, 777.92 +/- 52, 0.141 +/- 0.01, and 44.45 +/- 3.6, respectively. Additionally, 10mM ammonium nitrate is an economical and efficient nitrogen source for nitrogen assimilation of S. platensis, and 50 mu M iron is optimum for the growth of S. platensis. (C) 2014 International Union of Biochemistry and Molecular Biology, Inc.