Drobetskaya I. Influence of mineral nutrition conditions on growth and chemical composition of Spirulina platensis (Nordst.) Geitler

Subject: Spirulina platensis (Nordst.) Geitler. Aim: to establish influence of conditions of a mineral nutrition on growth and chemical composition of Spirulina platensis at various methods of cultivation. The relationships of the growth and metabolism of Spirulina platensis in dense semi-continuous and disproportionately continuous cultures (with a daily cycle) under open-air systems condition at natural light intensity and temperature have been established. It has been shown that concentrations of protein and antioxidant complex pigments of S. platensis at given cultivation modes are significantly higher than in batch culture. For the first time the data of protein and pigments contents in the biomass are used for calculation of spirulina system characteristics (reliability, organization, stability and complexity). It has been established that such parameters as protein, chlorophyll a and phycobiliprotein contents in biomass, C-phycocyanin percentage in total protein and phycocyanin:chlorophyll ratio are the fine physiologo-biochemical indicators of spirulina nitrogen nutrition conditions. For the first time it has been shown that for S. platensis in semi-continuous culture the value of economic nitrate coefficient positively correlates with a level of nitrates in the medium, but nitrate assimilation efficiency grows at deterioration of nitrogen nutrition conditions. It has been revealed that carbamide as an exclusive nitrogen source is of little use for S. platensis cultivation both in batch, and in disproportionately continuous culture. At the same time, partial replacement of nitrates by urea (up to 20 % on nitrogen) has stimulating effect both on growth rates of cultures and on activity of anabolic processes in the cells. Rate of selenium accumulation by S. platensis in semicontinuous culture positively correlates with element concentration in the medium. The selenium content in dry biomass reaches 14,3 - 24,6 mkg Se/g at medium selenite concentrations 10 - 15 mg of Se/dm3. On basis of developed antagonistic models it has been shown that the ratios of concentrations of selenium- and sulfur-containing metabolic products and also of the rates of their synthesis linearly depend on a ratio of selenium and sulfur concentrations in the medium. The obtained relationship between specific growth rate of cultures and the ratio of selenium and sulfur concentrations in the medium has been confirmed with experimental data.