Effect of cultivation conditions on polysaccharide synthesis by Skeletonema pseudocostatum

Microalgae are a source of biologically active substances, e.g., polysaccharides. Their commercial potential attracts a lot of scientific attention. This research featured the effect of various nutrient media on the biomass of the psychrophilic microalga Skeletonema pseudocostatum and its ability to synthesize polysaccharides. The Tamiya nutrient medium was used as the standard one. Its composition was improved to accelerate biomass cultivation. Optimization principles were based on the unconventional mathematical method for multidimensional modeling and involved the ANETR 21 software. The qualitative and quantitative assessment of microalgal polysaccharides relied on the anthrone sulfate method. The concentration of uronic acids was determined by the carbazole method while neutral sugars were studied by the resorcinol sulfate method in a microalgal suspension. The growth index of the S. pseudocostatum biomass was represented as a ratio of the maximal mass to the initial mass. The maximal growth index was achieved by adding to the standard Tamiya medium: 10.00 g/cm3 potassium nitrate (MgSO4×7H2O), 2.50 g/cm3 potassium dihydrogen phosphate, 1 cm3 Fe+ ethylenediaminetetraacetic acid (EDTA), and a mix of 4.29 g/cm3 boric acid and 0.9 g/cm3 manganese (II) chloride tetrahydrate (MnCl2×4H2O) in an amount of 1.00 cm3. The maximal polysaccharide biosynthesis was observed when the nutrient medium was modified as follows: 5.00 g/m3 potassium nitrate, 3.75 g/cm3 magnesium sulfate, 2.50 g/cm3 potassium dihydrogen phosphate, 1 mm3 solution of Fe+ ethylenediaminetetraacetic acid, and solution of 1.0 g/cm3 boric acid and 1.81 g/cm3 MnCl2×4H2O (1.00 mm3 each). The maximal accumulation of microalgal biomass was 2.88 ± 0.08 μg/100 mg dry solids; the maximal yield of polysaccharides was 3.16 ± 0.09 μg/100 mg dry solids. These results were obtained at 5°C. The yield of polysaccharides by S. pseudocostatum depended on such cultivation parameters as temperature and pH. At cultivation temperatures of 0, 5, and 10°C, the yield of polysaccharides reached 2.13 ± 0.06, 3.16 ± 0.09, and 2.04 ± 0.06 μg/100 mg dry solids, respectively. The yield of exopolysaccharides represented by uronic acids and neutral sugars was 106.3 ± 3.1 mg/g and 806.6 ± 24.0 mg/g, respectively. In this research, polysaccharides synthesized by S. pseudocostatum demonstrated good prospects for the food industry and sustainable organic agriculture.